Solid State Ionics

Organization

Preface

Contents

High energy density batteries, fuel cells, electrolysis cells, electrochromic devices, chemical sensors, thermoelectric converters or photogalvanic solar cells are solid state ionic devices of large practical interest in view of our energy and environmental problems. The engineering of new or improved devices is commonly based on individual materials considerations and their interaction in galvanic cells. Conflicts exist in view of the formation of chemically stable interfaces of functionally different electrolyte and electrode materials, simultaneous high energy and power densities because of commonly low conductivities of chemically stable materials, fast chemical diffusion in electrodes which should have a wide range of non-stoichiometry, practical problems of using less expensive polycrystalline materials which have high intergranular resistances and finally reaching both ionic and electronic equilibria at the electrolyte-electrode interfaces at low temperatures. Simultaneously high ionic conductivity and chemical stability may be reached by designing structures of large poly-ions of the non-conducting components. Electrodes should not be made of metallic conductors but of electronic semi-conductors with fast enhancement of the diffusion of the electroactive ions by internal electrical fields. Device considerations are based on the development of single element arrangements (SEAs) which incorporate the electrodes into the electrolyte in the case of fuel and electrolysis cells. The same simplification may be applied for electrochromic systems which consist of a single active layer instead of the conventional three materials. A new design of active chemical sensors probing the environment by the magnitude of the applied voltage or current may overcome the limitations of cross-sensitivities and interfacial reactions, which allows simultaneous sensing of several species by a single galvanic cell.

Mass transport phenomena in phosphoric acid, an important fuel cell compound, of varying concentration were studied by multinuclear NMR measurements including pulsed gradient spin-echo (PGSE) and static field gradient techniques. The latter method was developed in order to be able to measure self-diffusion as a function of applied hydrostatic pressure. The high pressure measurements were carried out at 288 K, and variable pressure up to 2.5 kbar. The high pressure data were obtained for four different concentrations of phosphoric acid in water in the range of 6% -100% by weight. The calculated activation volume for ¹H nuclei, increasingly dominated by the water protons, decreased as the acid concentrations decreased, exhibiting behavior approaching that of liquid bulk water. In addition ³¹P data show higher activation volumes than the corresponding ¹H data, mainly due to the larger molecular size of the phosphate groups compared to water molecules. This difference is a factor of two for 100% acid, suggesting a proton transport mechanism for high concentration acid which involves the hopping transfer of protons between the larger phosphate groups. Using ¹H and ³¹P pulsed gradient spin-echo techniques, self-diffusion coefficients have been measured for a range of phosphoric acid concentrations (6~100 wt %) over the temperature region from 293 to 363 K. The data show again that protons diffuse faster than the phosphorus carrying species. Different activation energies are obtained above and below 12 wt % acid concentration, suggesting the presence of ion association effects at this concentration.

Ionocovalent crystals or glasses as well as molten salts or salt polymer complexes are currently studied as electrolytes for high energy density batteries. Their large Red/Ox stability range results from their thermodynamic or kinetic characteristics.

For all these electrolytes, charge carriers are the consequence of local deviations from electroneutrality, identified as point defects for ionic crystals or partial dissociation in disordered structures. The charge carriers formation derives from a similar activated process.

The main difference comes from the migration process, which depends on the dynamic properties of the surrounding medium. When the structural relaxation time is large, an activated process, mainly enthalpic, prevails for charge carriers migration. It is the usual case for ionic crystals or glasses. In the liquid or overcooled liquid states, the structural relaxation time of the medium is shorter that the time required for the activated migration process to occur and a local reorganization of the medium vanishes the energy barrier and provides the free volume necessary to ionic migration. In that case, the migration is mainly an entropic process.

The configurational entropy necessary to this process decreases with temperature and vanishes at the so called ideal glass transition temperature which can be estimated by extrapolation of the transport properties or of the thermodynamic characteristics of the medium. However, at the experiment time scale, this configurational entropy disappears at a somewhat higher temperature, the glass transition temperature at which the structural relaxation time corresponds to the measurement time.

Some glass forming ionic melts studied in a large temperature scale, over and below the glass transition temperature, evidence the two, enthalpic and entropic, migration mechanisms, allowing the determination of the thermodynamic characteristics of the charge carriers formation and migration.

Some recent results indicate that entropic process, associated to long scale deformations, may also exist in crystalline structures.

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) experiments in solid electrolytes started around 1975 when a new interest arose in solids with high ionic conductivity. The emphasis of this revue is on experiments rather than theoretical issues. We will present typical NMR/NQR studies which demonstrate the power of these techniques to elucidate dynamic and static behavior of these solids at a microscopic level. Because of the overwhelming wealth of results accumulated in the last 30 years, we will be limited to some characteristic examples.

The dynamics of lithium ions in the polycrystalline fast ionic conductor Li_3xLa_2/3−xTiO₃ has been investigated by conductivity spectroscopy in the wide frequency range from 1Hz to 1GHz and by ⁷Li NMR spin-lattice relaxation measurements (T₁ and T_1ρ) in the temperature range from 150K to 600K. The results of T₁ and T_1ρ clearly reveal the presence of two thermally activated Li⁺ motions: a slow one, attributed to the long-range Li⁺ translation which gives rise to the dc conductivity and a fast one, attributed to a localised motion of Li⁺ in the A-cage of the perovskite. At high frequency, a dispersive behaviour of the conductivity with frequency is observed. The analysis of this dispersive behaviour along with the analysis of the activation energy of the ionic motion at fixed frequencies clearly reveal the existence of the correlated motion of the moving ions. The real microscopic energy barrier of the long-range ionic motion is obtained at high frequency and agrees with the values of ⁷Li NMR relaxation times measurements (T_1ρ) obtained at 62.5 kHz. These complementary techniques allowed us to describe the different motions of the moving ions in this oxide and to attain the real value of the microscopic energy barrier.

Starting from the simple bond valence (BV) concept commonly used to judge the plausibility of atomic positions in inorganic crystal structures, a method to analyze energy landscapes and to identify transport pathways for mobile ions in solid electrolytes has been developed. The approach is particularly valuable for analysing transport mechanisms and structure conductivity relationships in disordered solids, where the averaged information directly available from crystallographic methods cannot provide a sufficiently detailed picture. For systems where ion transport occurs in a nearly rigid matrix, e.g. ion conducting glasses, the BV analysis may be based on static structure models from reverse Monte Carlo fits to experimental diffraction data. The assumption that conduction pathways correspond to structure regions where the BV mismatch for the mobile ion remains below a threshold value then enables us to predict activation energy and ionic conductivity of ion conducting glasses from the relative volume of the percolating pathways in the structure model. Moreover BV mismatch landscapes provide further insight into transport mechanisms as they allow enumerating the number of accessible sites for mobile ions (irrespective of their occupancy), as well as quantifying the reduced local dimensionality or the medium-range ordering of transport pathways. The BV analysis of molecular dynamics simulation trajectories extends the application range to systems involving complex reorientation processes (provided that suitable empirical force-fields are available for a system) and permits to extract information on time and temperature dependencies.

Ice is a proton conductor, with conductivities ranging from 10⁻⁶ to 10⁻⁹ S m⁻¹ depending on the purity of the sample. Electronically ice is highly insulating with conductivity of the order 10⁻¹² S m⁻¹ or below. Mobile protons in ice originate from disruption of hydrogen bonds and strong electric fields enhance bond breakage. Ice particle acquires electrification during formation of thunder clouds and ice play a crucial in role charge separation leading to lightning. It is suggested that charges of ice particles in clouds originates from inductive charge separation and transfer of the mobile positive charge to the streaming air. Thus ice particles gain a negative charge and moist air drifting upwards becomes more positive. Consequently, most thunder clouds have a negative charge in the region closer to the ground.

Although many explanations are proposed, the elusive phenomenon of ball lightning continues to resist theoretical understanding and laboratory reproduction. Ball lightning originates in the electrical active atmosphere as a luminous sphere drifting in air with the capability of bouncing from walls and penetrating openings smaller than the ball. It is suggested that ball lightning is a negatively charged sphere constituted of an outer shell of ice. Water dipoles are oriented radially by the electric field and protons acquire a high mobility in the tangential direction. As the electron conductivity of the shell in radial direction is very small, the charge slowly leaks to the atmosphere as a corona discharge. Model naturally explains how the ball could penetrate a hole or bounce from a surface as a differential electrostatic stress could develop in the ball as result of the proton conductivity. Details of the models and suggestions for experimental verification of the proposed concepts will be presented.

Hydroxy apatite (Ca₁₀(PO₄)₆(OH)₂) is a ceramic material. This has been used for biological applications such as bone and teeth enamel. In this paper various preparation methods including sonochemical followed by microwave sintering technique has been used to prepare the material. The material was characterized by XRD, TEM, SEM and its electrical transport (proton) is measured by impedance spectroscopy. The conductivity measured is 0.091×10⁻⁶ to 19.20×10⁻⁶ Scm⁻¹ at 25 - 850°C range of temperature at 100 kHz applied frequency. Conductivity found to increase with increasing applied frequency at a given temperature of measurement. The prevalence of protons in the lattice has been confirmed by proton NMR studies. The results of the experimental observations on proton migration in the apatite lattice for electrical conduction are discussed.

The preparation of a pure and nanostructured phase of the fast lithium conductor Li_0.3La_0.56TiO₃ at low temperature (350 °C for 2 h) is reported for the first time. The synthesis has been carried out by the Pechini-type in-situ polymerizable method. It has been shown that the molar ratios ethylene glycol/citric acid and citric acid/metals, as well as the temperature, are crucial parameters during this synthesis. A careful control of the temperature during polyesterification allowed us to prepare nano-sized phase of oxide and to avoid the formation of thermally stable impurities. The crystallite size (20 –30 nm) of the oxide has been determined by the analysis of the broadening of the powder X-Ray diffraction lines. The particles size has been confirmed by Transmission Electron Microscopy and the macroporous character of the powder has been evidenced by Scanning Electron Microscopy.

Hydogen, H₂ is regarded as the main energy vector for the future. Today, the world production of hydrogen rises to 550 billion Nm³ (44 Mt) corresponding to 1,5% of the primary energy production. Contrary to fossil fuels, H₂ does not exist in a native form and its use obviously requires its fabrication and storage. The future status of H₂ as a fuel for electricity production (fuel cells) and for automobile transportation makes necessary a considerable increase of its production. Some H₂ manufactoring processes are briefly described in the first part of this article : (i) steam methane reforming, (ii) water decomposition by thermochemical cycles, (iii) water decomposition by photoelectrochemistry, (iv) water or organic compounds decomposition in using bacteria or alguae. The second part concerns the H₂ production by water electrolysis. This manufactoring process does not exceed 1% of the total production of hydrogen. It is expected that the electrolysers working at high temperature (700-900°C) using ceramic oxides based electrolytes are the more promising. Two groups are considered: electrolysers with proton conductors or oxide ion conductors as electrolytes. Proton conductors belong to the perovskite oxides family MCe_1−xLn_xO₃ with M = Ba, Sr and Ln = Lanthanide. For these conductors, few results on water electrolysis at high temperature are available in the litterature and will be shown here. Electrolysers using oxide ion conductors are more promising. The selected materials are those developped for SOFCs : YSZ for the electrolyte, Ni based cermets for the cathode materials and La_1−xSr_xMO_3±δ with M = Mn, Co, Ni, Fe … The electrochemical characteristics of the anodic and cathodic interfaces as well as the perfomances of electrolysers working at high temperature are presented.

The ability of Li_0.30La_0.56TiO₃ ceramic surface to respond to pH variation has been investigated. The influence of the heat-treatment (or sintering temperature) of the membrane after synthesis on its surface sensitivity has been studied by potentiometric measurements and Electrochemical Impedance Spectroscopy (EIS) with a four-electrodes symmetric cell in different pH buffered solutions. These techniques allowed us to determine the thermodynamic and the kinetics parameters of the oxide surface. The sub-Nernstian response can be explained by means of the site-binding model that describes the charging mechanism of oxides by surface reactions. The intrinsic buffer capacity, β_int, of the oxide surface is a key parameter that defines the response of the pH sensor. We will discuss how this parameter influences the properties of the surface oxide and therefore the sensitivity of the membrane to pH variations.

Nano-sized Ce_(1−x)Sm_xO_2-δ (x = 0.05 - 0.2) were synthesized through combustion synthesis route. The thermo-chemical properties of the precursor were studied by TGA/DTA. Crystal structure and microstructure were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The complex impedance spectroscopy used to evaluate contribution from grain, grainboundary and electrode-electrolyte interface in the temperature range 200 - 700°C reveals that the dopant concentration not only influences the conductivity of grain, but also that of grainboundary. Concurrently, total conductivity exhibits maximum for x = 0.15

The scope of the studies is to explore electric and magnetic properties of Fe³⁺ ion rich red soils in Northern Sri Lanka. Six samples were collected at different locations in Northern Jaffna peninsula, Sri Lanka for this investigation. Reported studies involve current-voltage (IV) measurements at room temperature of fresh, moisture-freed (115°C at 48 hrs), and annealed (1000°C at half an hour) conditions. At the fresh condition moisture dominates and is responsible for much of its transport properties. However, we are reporting that Fe³⁺ ions influence its transport properties in the moisture-freed and annealed conditions. Even though moisture-freed and annealed samples follow sub-linear IV behaviour the quantitative values suggest that the samples are very close to insulators (or semiconductor-insulator boundary). High field magnetization measurements up to 7 T at 1.8 K show all the samples reach the saturation moments around at 2.5 T, where the behaviour is very much similar to ferromagnetic materials. The highest saturated moment reported is ~10⁻³ μ_B/Fe³⁺ and the lowest is 6.5×10⁻⁴ μ_B/Fe³⁺. Also, we are presenting the inverse magnetic susceptibility-temperature (1/χ(T)) measurements from room temperature (300 K) down to 1.8 K, which suggest that critical temperature T_c is around 30 K. Perhaps, the red-soil be a natural magnetic ceramic.

Neutron scattering experiments have been performed on LiNiO₂ composites at room temperature. Rietveld refinement analysis on the neutron scattering results of LiNiO₂ was performed by assuming hexagonal type structure with space group R-3m. The analysis of crystallite size of LiNiO₂ is performed from the FWHM of the Bragg lines using Scherrer equation. It is found that the crystallite size of LiNiO₂ increases with the increase of annealing temperature. The intensity of the Bragg lines and the background scattering of LiNiO₂ composites have been used to estimate the percentage of LiNiO₂ formed in the annealing process.

LiFePO₄ nanorods have been synthesized using a rheological reaction followed by a self-assembling process, and characterized by XRD, TEM, FTIR, cyclic voltammogram, model battery, etc. The results show that the LiFePO₄ nanorods with length of 50∼100 nm and nanorod diameter of 20∼50 nm are grown orderly with certain direction, resulting in better conductivity and insertion/extraction reversibility of Li⁺ ions.

This work reports new trends on the structural and electrochemical properties of two polymorphs of the well-known Mo-O system. Two crystalline phases have been obtained: the monoclinic β-MoO₃ and the orthorhombic α-MoO₃. The structure and morphology of these oxides were studied as a function of the temperature and the ambient of heat treatment to determine the optimum conditions for single phase synthesis. Results from XRD, SEM and Raman measurements are presented. The electrochemical lithium intercalation into the prepared trioxides was attempted as the intercalation host for secondary lithium batteries Cycling performance showed a high ability of both polymorphs to form lithium intercalation compounds. For the β-MoO₃ phase, the maximum lithium uptake 1.9 Li⁺/Mo leads to the gravimetric capacity 353 mAh/g, while the α-MoO₃ phase develops a specific capacity 298 mAh/g for 1.6 Li⁺Mo inserted.

The feasibility of the preparation of doped zircon (ZrSiO₄ or ZrO₂.SiO₂) via solid state sintering of precursor oxides (ZrO₂ and SiO₂) and the dopants has been investigated. In this study, Y₂O₃, Yb₂O₃, Fe₂O₃, CaO, MgO, Li₂CO₃ and Na₂CO₃ were used as dopants with a concentration level of 10 mol %. The sintered pellets were subjected to X-Ray Diffraction (XRD) analysis and the zircon yield was calculated using the XRD data. It was revealed that the zircon yield in the dopant oxide added samples was very high (57-100% depending on the dopant) and the ionic radius difference between the host Zr⁴⁺ and the dopant cation has a direct implication with the zircon yield. Although it could be observed that the addition of trivalent or divalent cations enhanced the zircon yield, addition of monovalent cations completely hindered the zircon formation.

The planar specimen of ZnTe:V cermet films as well as ZnTe films were prepared onto glass substrate by e-beam evaporation of the element in vacuum at ∼10⁻⁶ torr. The effects of various deposition conditions on the electrical properties of the cermet devices have been studied in detail. It is found that ambient pressure, source to substrate distance and beam current play important role in obtaining films. The deposition rate of the films was maintained at about 2.05 nms⁻¹. The current-voltage characteristics of vacuum deposited ZnTe:V cermet thin films were studied under the high electric field (>10⁶ Vm⁻¹) as a function of film thickness ranging 100 to 200 nm and containing 0 to 10% V in ZnTe matrix at temperature ranging 300 to 413 K. The composition and thickness dependence of the activation energy as well as thermoelectric power measurements were done in the 300 to 413 K temperature ranges. The results of dc conductivity and thermoelectric power obey an activated conduction mechanism. Thermo power result also suggests that the simultaneous bipolar conduction of both carriers take place.

A computer simulation by a molecular dynamics method is performed to study the properties of structure and Li ion diffusion in La_4/3−xLi_3x□_2/3−2xTi₂O₆ (□=vacancy), which is the perovskite-type Li ion conductor. In the low Li concentration, Li ions conduct a two-dimensional motion, while Li ions diffuse a three-dimensional motion in the high Li ion concentration. The partial distribution function for Li-Ti and the diffusion paths of Li ions suggest that Li ions stay for a long time at off-site positions which are 2.7Å away from a body-centered Ti ion. The Li ion concentration dependence of σ is in approximate agreement with experiments. The energy band dispersion and the density of states are calculated using the linear-muffin-tin-orbital (LMTO) method. The energy contour map shows the stable position of Li ions is off centers of the vacant La sites.

Solid state polymer–Silicate nanocomposite based on Polypyrrole-Cu⁺-montmorilonite were prepared and electrical properties were investigated. In this preparation, Na-montmorillonite (Na⁺-MMT) was purified by repeated washing with distilled water and the intergallery cations were exchanged for Cu(II). The cupric ions exchanged-MMT(Cu(II)⁻- MMT) was again exposed to pyrrole in aqueous acidic solution to yield polypyrrole-Cu⁺-MMT nanocomposite. DC polarization test and AC impedance measurement reveal that the materials are mixed conductors. The ionic conductivity is due to the motion of cuprous ions which is facilitated by microstructure of polypyrrrole present in the intergalleries. An electrochemical cell was fabricated using the materials which can be represented by Cu_(s)/ Cu⁺-PPY-MMT/Cu₂SO_{4 (s)}/Na₂SO_4(S)-Na₂S₂O_8(s)/ and gave a 1.00 V. The cell is rechargeable.

The ionic conductivity as a function of frequency has been studied on a newly synthesized fast Ag* ion conducting mixed system/solid solution; [0.75AgI:0.25AgCl]. In the present paper dc conductivity as a function of frequency and temperature has been studied, activation energy (Ea) values were calculated from Arrhenius plots and compared with the ac conductivity. Ionic transport parameters of the present superionic system have already been reported earlier. Log σ vs. log f variation shows dispersion at higher frequency region and obeys Jonscher's power law.

Diffuse X-ray and neutron scattering from powder PbS were measured at 15 and 294 K. Oscillatory diffuse scattering was clearly obtained at 294 K. The values of correlation effects decrease with the increase of inter-atomic distance. As the scattering amplitude (f_pb) in X-ray scattering and scattering length (b_pb) in neutron scattering of Pb are much greater than those of S (f_s, b_s), the contributions to the oscillatory diffuse scattering from the thermal correlation between second nearest neighboring atoms (Pb-Pb) were observed by X-ray and neutron scattering. The clear contribution to the diffuse scattering from second nearest neighboring atoms was first obtained.

Undoped MnO₂ thin films have been prepared by a modified spray pyrolysis technique onto glass substrate in the thickness range 85-380 nm at a deposition rate of 6.7 nm/min and the effects of different variables on electrical and optical properties has been studied in detail. X-ray diffraction and Transmission Electron Microscopy studies show that MnO₂ films are homogenous and polycrystalline in structure. The Hall effect and thermoelectric studies indicate that the deposited samples are n-type semiconductor. Optical study in the entire wavelength range 0.3-2.5 μm range exhibits a high transmittance in the visible as well as in the infrared. The position of Fermi-level (E_F) is obtained from thermoelectric measurement and optical data exhibits a value of band gap. The calculation of electron affinity and work function are done in the polycrystalline MnO₂ samples. Their values are 2.94 to 297 eV and 2.83 to 287 eV, respectively. The calculation reveals that the bond between manganese and oxygen are considered as the principal bond and within the limits of native and foreign impurity contents, MnO₂ is more co-valent than ionic which supports the results of earlier works.

The proton conductor Ba₃Ca_1.18Nb_1.82O_8.73 (BCN18) was synthesized by a method of solid state reaction. The structural and thermodynamic properties were studied for dry BCN18, water-solved sample (BCN18-H) and deuterated water-solved sample (BCN18-D), by dielectric permittivity and heat capacity measurements, and by powder X-ray and neutron diffraction experiments carried out at SPring-8 and at JAEA, respectively. The existence of OH(OD) group in the water-solved samples was confirmed, and the motion of the group above 230 K was discussed.

The vanadium oxide thin films have been prepared by thermal evaporation method. The films coated on glass and silicon substrate are subjected to vacuum annealing at 573K. The X-ray diffraction analysis shows both as deposited and annealed films are amorphous in nature. Scanning Electron Microscope (SEM) analysis shows vacuum annealed films has smooth surface topography, which is suitable for device applications. X-ray photoelectron spectroscopy (XPS) study shows that the as-deposited vanadium oxide films and vacuum annealed films are sub-stoichiometric nature. Further, the presence of vanadium in lower oxidation states i.e.V⁴⁺ suggests that the chemical composition of the film is partially vanadium pentoxide (i.e, V_2−xO_5−y). Electrical characterization shows that the resistance of the vanadium oxide film is ~10⁶ Ohms. Frequency dependent conduction and impedance studies shows the high resistive electronic conduction process.

La_1.9Sr_0.1NiO_4+δ with a pure K₂NiF₄ phase was synthesized from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H₅DTPA) as ligand, and the effect of sintering temperature on the microstructure and mixed electronic-ionic conducting properties of La_1.9Sr_0.1NiO_4+δ ceramic was investigated in the range of 1400-1600 °C. Homogeneous and fine powder (100-200 nm) with a pure K₂NiF₄ phase was produced by calcining the complex precursor at 900 °C for 2 h in air. The increase of sintering temperature promoted the microstructural densification. Compared with a gradual increase of grain size with sintering temperature in the range of 1400-1500 °C, there is an exaggerated grain growth in the specimens sintered at 1550 °C and 1600 °C, respectively. Increasing sintering temperature from 1400 °C to 1500 °C resulted in an enhancement of electrical and ionic conducting properties. Further increase of the sintering temperature above 1500 °C declined the electrical and ionic conducting properties. The variation of the mixed conducting properties with sintering temperature was interpreted for the viewpoint of microstructural evolution. With respect to the mixed conducting properties, the preferred sintering temperature was ascertained to be 1500 °C for La_1.9Sr_0.1NiO_4+δ. The specimen sintered at 1500 °C exhibits an electrical conductivity of 86 S/cm and an oxygen ionic conductivity of 3.8×10⁻² S/cm at 800 °C.

High energy vibrational ball milling device was used under argon atmosphere to prepare two series of nanocomposite of MgH₂ with 5%wt. M (M= Fe, FeF₃ and VF₃) in order to improve the hydrogen storage sorption of the magnesium hydride. Morphology, structural and thermal characterization of the MgH₂ composites was performed by using XRD, SEM and simultaneous TG and DSC techniques. Electrochemical study of hydrogen charge-discharge process in MgH₂ provides distinct information on thermodynamic and kinetics of the Mg-H₂-catalyst system. Electrode potential provides information on the variation of the free Gibbs energy carried out by surface energy modification generated by nanometric grain size and catalyst. Current density of voltammograms reveals improvements carried out by different catalysts on hydrogen sorption-desorption kinetics.

Amorphous solid electrolytes in the system xLi₂S-(1−x)P₂O₅ (with x = 0.5, 0.6, 0.7) has been prepared from a mixture of Li₂S and P₄O₁₀ using a mechanical milling technique at room temperature and in inert atmosphere. The oxysulfide powder mechanically milled for 80h with x=0.6 shows ionic conductivity (σ) of 7.89 × 10⁻⁶ S/cm at room temperature which is the highest in this series. The glass transition temperature (T_g) increases with the increase of Li₂S. X-ray RDF analysis and constant volume molecular dynamics was done for all x. Both Phosphorous and Lithium were found to coordinate with both oxygen and sulfur in various proportions. Various units present around phosphorous and lithium are PO₃S, PO₄, PO₃, PO₄S, LiO₃S, LiO₃, LiO₂S, LiO₄. Changes in structure with x and their influence on σ and T_g are discussed.

Bi₂V_0.9Cu_0.1O_5.5−δ powder was synthesized by a sol-gel method using EDTA and citric acid as mixed complexing agents. The formation process as well as the phase development and morphology of the synthesized powders were characterized by TG-DSC, XRD and SEM. The results indicate that fine and homogeneous powder (100-200 nm) with a pure Aurivillius phase can be produced by calcining at 450 °C for lh. Compared with the conventional solid state method, the synthesizing method used in this work demonstrates remarkable advantages in producing Bi₂V_0.9Cu_0.1O_5.5−δ powder, such as simplicity and lowing calcining temperature. The oxygen ionic conducting properties of the ceramic specimen were investigated using AC impedance spectroscopy. The influence of sintering temperature on the microstructure and oxygen ionic conducting properties of Bi₂V_0.9Cu_0.1O_5.5−δ ceramic was investigated in the range of 560-680 °C. The ceramic specimen sintered at 640 °C for 2h shows a dense microstructure with an average grain size of about 3 μm and a relative density of 93.6 %. The specimen provides an oxygen ionic conductivity of 1.4×10⁻¹ S·cm⁻¹ at 600 °C. The difference between the activation energies for the oxygen ionic conducting in low and high temperature ranges is tentatively interpreted in terms of an order-disorder transformation.

The present work involves the preparation and characterization of a new superionic system namely, (PbI₂)_x -(Ag₂O–Cr₂O₃)_100−x where x = 5, 10, 15, 20, and 25 mol% respectively. The varieties of samples were synthesized by the rapid melt quenching technique. Complex impedance analysis of all these samples was carried out over the frequency range 1 MHz – 20 Hz in the temperature window 300 – 463 K. The Fourier transform infrared (FTIR) spectra were recorded over the wave number region 4000 – 500 cm⁻¹ by the KBr pellet method at room temperature. Furthermore, the ionic transport number (t_i) values were obtained for all these specimens by Wagner's polarization technique. Impedance spectral analyses have indicated their room-temperature electrical conductivities to be of the order of 10⁻⁴ Scm⁻¹.The detailed FTIR results obtained for most of the samples in this system have revealed the absorption bands around 850 cm⁻¹ corresponding to CrO₄²⁻ molecular species. The ion transport number values as determined by the Wagner's polarization method were found to be greater than 0.95 thus indicating the ionic nature of this system for device applications.

Electronic conductivity of cobalt doped LSGM electrolytes (La_0.8Sr_0.2Ga_0.8Mg_{0.2− x}Co_xO_3−δ, LSGMC) was directly measured with using a Hebb-Wagner's ion blocking cell. Electronic conductivity of LSGMC electrolytes was measured as a function of oxygen partial pressures. The electronic conductivity of LSGM8282(LSGMC(x = 0) electrolyte shows a linear dependence on p(O₂)^1/4 in the higher p(O₂) region, which is attributed to the electronic hole conduction. The electronic conductivity of LSGMC was drastically changed with the concentration of cobalt. The electronic conductivity of LSGMC(x = 0.01) also shows a linear dependence on p(O₂)^1/4 in the higher p(O₂) region, and the conductivity was about the same with that of the LSGM8282. On the other hand, the electronic conductivity of LSGMC(x = 0.05) did not show a linear dependency on p(O₂)^1/4 but on about p(O₂)^1/6 in the higher p(O₂) region. The electronic conductivity of both electrolytes in lower p(O₂) region did not show any dependence on p(O₂).

Layered Li(Co_1−xAl_x)O₂, x=0.05-0.25 phases have been prepared by using the one-pot molten salt method at 850 °C in air and characterized by X-ray diffraction, Rietveld refinement, SEM-EDAX, chemical analysis, BET surface area and density methods. Cathodic properties were studied at ambient temperature in cells with Li-metal as the counter electrode by cyclic voltammetry (CV), galvanostatic charge-discharge cycling (up to 130 cycles) and Impedance spectroscopy. Single-phase compounds with hexagonal layer structure formed for all x. Results showed that for x≥0.05, the Li-de-intercalation potential during the first charge-cycle occurs at a value slightly higher than that shown by pure LiCoO₂ and the structural transitions that occur at ∼4.1 V and ∼ 4.2 V are suppressed. However, the transition at ∼4.5 V is not suppressed. As a consequence, the long-term cyclability of Li(Co_1−xAl_x)O₂ is greatly improved, when cycled in the potential ranges 2.5-4.3 V and 2.5-4.4 V at the current rate of 30 mA/g. Higher 10^th cycle capacities were noted for x≥0.1-0.2 in the 2.5-4.5 V range but capacity-fading was noted, by 5-7 % at the end of 55 cycles. The observed CV and impedance data have been analyzed and interpreted.

No abstract received.

LiNi_0.80Co_0.20O₂ thin-films have been prepared by RF magnetron sputtering on Pt substrate. The films before and after annealing were identified by XRD, SEM and electrochemical measurements. The as-deposited film was amorphous phase. After annealing at 600∼800 °C, well-crystallized LiNi_0.80Co_0.20O₂ films were obtained. The degree of crystallization of the as-deposited films is strongly affected by the annealing temperature. As a result, the 700°C-annealed film has relatively complete layered structure, high specific capacity and good cycleability. The first discharge capacity of the LiNi_0.80Co_0.20O₂ film annealed at 600, 700 and 800°C is about 44.5, 55.3 and 46.2 μAh/cm²·μm, respectively. The corresponding 50^th discharge capacities are 40.2. 49.4 and 42.4% of the first discharge capacity.

Electrostatic spray deposition (ESD) technique was applied to deposit composite electrodes, which consisted of a mixture of a solid electrolyte (YSZ) and an electrocatalytic material (LSM) with a controlled microstructure on YSZ dense substrates. The influence on film morphology of the process parameters such as nature of precursor solution, deposition temperature, nozzle to substrate distance and precursor solution flow rate was investigated. The results demonstrated a significant role of the salt nature in the precursor solutions in the film morphology. In this work, powder X-ray diffraction analysis showed that no traces of any secondary phases were detected in between LSM hexagonal and cubic YSZ phases after thermal treatment at 800°C, this latter preserving the microstructural properties.

We studied the effect of nanoporous carbon black (non-graphitized carbon) on the electronic conductivity of recently identified Li₂Co₂(MoO₄) polyanion material, for which the lattice level conductivity is low similar to the other polyanion materials reported so far irrespective of their structure. Li₂Co₂(MoO₄)₃ was found to possess improved conductivity due to the addition of a highly conducting nanoporous carbon black (NCB) as conductive additive besides acetylene black. Inclusion of non-graphitized carbon black facilitated the effective grain-grain contact leading to increased surface particle conductivity between the active grains and thus resulted in enhanced overall conductivity of the electrode in a composite manner. The nano-composite test electrode fabricated with NCB rendered improved charge/discharge properties in the voltage window 4.9 – 2.0 V, when compared to the conventional composite electrode. Accordingly, the nanocomposite electrode delivered the first discharge capacity of 55 mAh/g, about 2.5 times higher than the capacity offered by the conventional composite electrode (23 mAh/g). It was also demonstrated that the presence of NCB enhanced the extended cycling performance in terms of Li⁺ insertion and retention of the host structure of the electrode material.

TiP₂O₇ was synthesized by reacting TiO₂ and 85 % H₃PO₄ and characterized by XRD, TEM and SEM. The electrical conductivity of the sample was examined at 500-1000 °C under various p(O₂), p(H₂O), and p(D₂O) conditions. The conductivity of the material in wet atmospheres was higher than that under D₂O-containing and dry atmospheres, indicating that protonic conduction was dominant in this material in wet atmospheres. The conductivity was mainly independent of p(O₂) at 500-900 °C under oxidizing conditions, confirming predominant ionic (protonic) conduction.

Thin film electrode of spinel LiMn₂O₄ for rechargeable lithium micro-batteries was prepared by a solution deposition route. The Li-Mn-O solution was deposited on electronically conductive Au substrate by a spin coater. By controlling the fabrication condition, the excellent rechargeability was observed in a test cell which contained the LiMn₂O₄ film. XRD and SEM were used to characterize the structures, phase composition, morphology of the thin films. The thermal decomposition behavior of the precursor powder was examined by TG/DSC to determine the temperature of heat-treatment. The electrochemical properties of the thin films were also investigated using cyclic voltammeter (CV) and charge/discharge cycling. The thin films obtained from the optimal processing condition (Li/Mn=1.05:2. dried at 280°C. annealed at 800°C for 30min) were homogeneous, crack-free, and showed good cycling behavior. The capacity loss is about 1.54% after 100 cycles at current density of 50μA/cm².

LiNiPO₄ and LiCoPO₄ cathode materials based on Phospho-Olivine structure have been prepared by Pechini – type Polymerizable Technique. Structural and thermal analyses have been done using XRD and TGA/DTA respectively. Formation of nano sized particles has been confirmed from the XRD analysis for both the samples. Conductivity analysis shows the conductivity in the order of ∼ 10⁻⁵ Scm⁻¹ for both LiNiPO₄ and LiCoPO₄ at 303K. Transport parameter such as hopping frequency has been calculated from the conductance spectra.

Binary and ternary compositions of LiFeO₂, LiCoO₂ and NiO were synthesized and electrically characterized, aiming the application in electrodes of fuel cells and batteries. Materials synthesis were carried out through wet-chemical routes, such as Pechini and glycine-nitrate techniques. Calcination and sintering studies were performed in order to find the optimum conditions for these new materials. The sintered materials were subjected to phase analysis by X-ray diffraction and the electrical conductivity measurements were performed by the d.c. 4-probe method up to 750°C.

The powders prepared by Pechini method result in rather spherical and softly agglomerated particles. The phase analysis reveals the existence of LiFeO₂-LiCoO₂-NiO solid solution phases of Fm3m cubic rock-salt structure in LiFeO₂-NiO rich compositions. Increase of the LiCoO₂ content of the composition results in the formation of R3m layered phase. Electrical conductivity of LiCoO₂-NiO binary compositions increases drastically with the LiCoO₂ content. While the conductivity is considerably low and decreases with the LiFeO₂ content in NiO-LiFeO₂ and LiFeO₂-LiCoO₂ binary systems. In the ternary system, the electrical conductivity increases to a maximum with increasing LiCoO₂ content. Altogether, this study shows the behaviour

The performances of γ-MnO₂ cathode in alkaline battery depend on the crystallochemical properties of MnO₂ as well as of graphite used to improve electronic conductivity of the cathode mixture. In the present work we have studied the performances of Sri Lanka natural graphite in the reduction process of γ-MnO₂ and compare it with the other synthetic and natural graphites. We also show how crystallochemical and electrochemical properties of the synthetic manganese dioxide depend on defects which are related to the structural parameters P_r and T_w. Where P_r is the rate of ramsdellite-pyrolusite intergrowth and T_w microtwinning which represents the creation of nanostructure aggregates during electrodeposition.

LiNi_1−(x+y)Al_xZn_yO₂ composition (x = 0.0-0.10, y = 0.0-0.005 ) substituted with Al³⁺ and Zn²⁺ was synthesized by an emulsion method and electrochemical properties were investigated. Emulsion-derived powder has porous spherical shape agglomerated with fine particles. The calcined powder was agglomerated shape with nanosized particle under 50nm. The intercalation of Li⁺ is higher in LiNi_1−(x+y)Al_xZn_yO₂ than pure LiNiO₂. The 1^st discharge capacity and fade rate for 20 cycles were 161 mAh/g, 8.5% in LiNiO₂, 168 mAh/g, 7.1% in LiNi_0.99Al_0.01O₂, 163 mAh/g, 5.5% in LiNi_0.995Zn_0.005O₂ and 164 mAh/g, 7.4% in LiNi_0.992Al_0.006Zn_0.002O₂ respectively.

A particulate sol-gel (PSG) method has been successfully developed to prepare LiNi_0.80Co_0.20O₂ cathode materials, utilizing the reaction of LiOH · H₂O with Ni(CH₃COO)₂ · 4H₂O and Co(CH₃COO)₂ · 4H₂O in water-ethanol system. The thermal history of the as-prepared xerogel was established by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Powder X-ray diffraction (XRD) confirmed the formation of well-layered α-NaFeO₂ structure at temperature of 700 °C under flowing oxygen. Scanning electron microscope (SEM) exhibited that the crystalline powder prepared by PSG method had relatively smaller particle size with narrow distribution than the one prepared by solid-state reaction. The first discharge capacity of the material prepared by PSG method was 193.5 mAh/g, and the 15^th discharge capacity was 185.1 mAh/g at the current density of 18 mA/g between 3.0 and 4.3 V. Its cycling reversibility was observed to be much better than that of the one by solid-state reaction, which had 182.9 mAh/g of the first discharge capacity and 162.0 mAh/g of the 15^th discharge capacity

Thin films of LiCoO₂ and LiMn₂O₄ were prepared by pulsed laser deposition technique. The influence of deposition parameters on the structure and surface morphology of the films were studied. The LiCoO₂ films deposited in oxygen partial pressure of 100 mTorr and at substrate temperature of 300 °C exhibited predominantly (003) orientation of the hexagonal R-3m phase indicating that the growth occurs perpendicularly to the substrate surface with an average grain size of 80 nm. Whereas the films grown at higher substrate temperature were polycrystalline with the growth parallel to the substrate surface. The LiMn₂O₄ thin films prepared at 300 °C exhibited predominantly (111) orientation indicating cubic spinel structure with Fd3m space group.

LiNi_0.80C_0.20O₂ thin films were prepared by spin-coating method using sol-gel, and annealing process. The thermal decomposition behavior of the precursor was investigated by thermiogravimetry/difierential thermal analysis (TG/DTA). The crystallinity and microstructure were studied by X-ray difieraction (XRD), scanning electron microscopy (SEM). Films annealed at 700 °C for 60 min exhibit 58.4 μ Ah/cm²· μ m of the initial capacity and better capacity retention and are therefore considered to be candidates as cathodes for all solid-state thin-film microbatteries. The film electrochemical properties depended on the annealing temperature and time.

Intercalation of lithium into the vacant sites of a host compound can be achieved electrochemically using non-aqueous electrolytes. The use of aqueous electrolyte is less common because of the reactivity of many lithium intercalation compounds with water. Here we propose that lithium could be intercalated using aqueous solutions, lithium hydroxide as the electrolyte. The X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Secondary ion mass spectrometry (SIMS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. A significant improvement in cell performance was obtained by adding small amounts (< 3 wt %) of titanium disulphide (TiS₂) to the cathode.

Rechargeable thin-film batteries have become the topic of widespread research for use in low power applications in the field of Microelectronics and in Microsystems. The fabrication of lithiated vanadium oxides such as LiNiVO₄ and LiCoVO₄ in thin-film form is of great interest as a result of their possible use as electrode materials in all-solid-state lithium rechargeable microbatteries to power microelectronics. In the present study the preparation of lithium nickel vanadate thin films using Pulsed Laser Deposition technique and their electrical characteristics have been reported. The XRD analysis confirms the formation of thin film LiNiVO₄. The impedance analysis gives the grain interior and grain boundary resistance as 3×10⁻⁴ ohms and 8×10⁻³ ohms at 623 K respectively. The conductance spectra indicated the electrode polarization effect of the thin film sample. The modulus analysis indicated the non-Debye nature of the sample. The dielectric spectrum shows a low-frequency dispersion of the dielectric constant, which reveals the space charge effects arising from the electrode.

We report on a novel synthetic method of microwave processing with a domestic 2450MHz microwave synthesis system to prepare LiFePO₄ cathode materials. We also studied and report on structure and morphology of the resultant products via three raw materials by XRD and SEM. XRD revealed that a single phase LiFePO₄ powder can be synthesized quickly and easily by microwave processing. The results indicate that microwave processing is a promising method of processing LiFePO₄ cathode materials.

The perovskites with nominal compositions Nd_0.8Sr_0.2CoO_3−δ were fabricated as cathode materials of low-temperature operating solid oxide fuel cells (SOFCs) using a solid-state reaction method. The Pt solution to improve electrical properties at low temperature was dispersed into cathode material. X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance was measured in the temperature range of 600-900°C in air and fitted with a Solatron ZView program. The crystal structure, microstructure, impedance spectra, and polarization resistance of Nd_0.8Sr_0.2CoO_3−δ were characterized systematically.

Sri Lanka natural vein graphite has various morphologies with different structural and physical characteristics. The identified most abundant morphology, the shiny-slippery-fibrous (SSI) graphite found in two mines, Bogala and Kahatagaha-Kolongaha, has a very high purity over 98% and high crystallinity. The characterization of Li-graphite intercalation process was mainly performed with the initial discharge-charge profiles at the current rate of C/20 and C/40, and cycled between the initial open circuit voltage and 0.005 V vs. Li/Li⁺ in lithium cells in 1M LiPF₆ (EC/DMC; 1:1). The synthetic KS25 graphite showed much better rechargeability and higher intercalation rate of lithium ions than natural BSSI and KSSI graphite. The irreversible capacity loss of natural vein graphite was partly due to passivation and exfoliation. But the major irreversible capacity loss of the graphite (natural or synthetic) was mainly due to lithium trapping in the internal pore spaces of graphite material or electrode structure. Measurements of the open circuit voltage in lithium cells with graphite as working electrode were used to obtain the thermodynamic factors such as entropy, ΔS, and enthalpy, ΔH, of lithium intercalation into natural and synthetic graphite. These thermodynamic values were determined in discharging process of the lithium cells from 0.005 V to 1.50 V vs Li/Li⁺ at C/5 rate. For all the types of graphite, initially large ΔS decreases with lithium concentration and then becomes negative and shows three entropy plateaus indicating the transition of stages in graphite-lithium intercalation compounds. For natural and synthetic graphite ΔH is negative and increases with lithium concentration and follows the staging process of lithium intercalation.

Ionic states in amorphous polymer electrolytes are discussed suggesting that uncoupled neutral and charged aggregates are the more mobile. Low-dimensional systems designed so as to suppress interactions with the polymer and to promote uncoupled aggregates within 2-dimensional cavities are described. The mixed polymer-Li salt systems include block copolymers C180105 (I) having an ionophobic mesogenic block (CmO1) and an ion-separating block (CmO5) together with an intercrystalline ion-bridge tetrahydrofuran copolymer III to sustain conductivity of the liquid crystal (lc) phase into the crystal (c) phase. New results describe the replacement of the ionophobic mesogenic block CmO1 by the more mechanically flexible C1802. ⁷LiNMR indicates high Li mobility in C1802 :LiBF₄ but lower levels of conductivity (3 × 10⁻⁴ S cm⁻¹ at 20°C) than in CmO1 copolymers were observed on slow cooling from the isotropic through lc and c states.

Polymer electrolytes may in some aspects be compared to traditional low permittivity liquid electrolytes. The solvation process of a salt involves a competition between interionic and ion-dipole forces. For liquid electrolytes a dissolved ion is surrounded by a primary solvation sheath which is carried along with the moving ion. This means that the interaction between dipoles of the solvation sheath and free dipoles is of great importance for ionic transport. For polymer electrolytes we do not have a primary solvation sheath in the traditional sense since the surrounding dipoles are parts of the polymer chain and thus limited to only a local movement. Ionic transport is in this case involved with a rearrangement of the nearest surrounding dipoles. That is, while an ion is moving the coordinated dipoles are continuously replaced by other dipoles and this thereby provides a possibility for the ion to move. Ion transport is therefore possible in spite of the coordination to dipoles which are restricted to a more limited region. Since this study is limited to low permittivity solvents we know that the salt does not dissociate completely. Ion pairs, triplets and even larger ionic species exist in equilibrium with dissociated ions. For a 1,1-electrolyte ion pairs are the most obvious dipoles with dipole moments probably larger than the (low permittivity) solvent dipoles. This is seen as a rapid increase followed by a saturation of the static permittivity, ε_S, with increasing salt concentration. The static permittivity mirrors the dipolar properties of the material where mainly ion pairs and solvent dipoles contribute. In this paper ionic association and transport is discussed in terms of dielectric properties, conductivity and thermal properties for polymer electrolytes with and without filler materials.

H⁺, Na⁺ and Li⁺ ion conducting polymeric composites have been prepared by using two different Sr²⁺-doped BaTiO₃ ferroelectric ceramics as dispersoids viz. (i) Ba_0.88Sr_0.12TiO₃ having T_C∼90°C, abbreviated as BST 90 and (ii) Ba_0.70Sr_0.30TiO₃ having T_C∼30°C abbreviated as BST 30. The dielectric constants of BST 90 at 20 °C and its dielectric phase transition temperature T_c (where ε is highest) are respectively ∼1100 and ∼5500 while for BST 30 the corresponding values are ∼2400 and ∼7500. The values of σ at 20°C for BST 30 dispersed samples for all compositions have been found to be higher than those having BST 90 as dispersoid because of the higher dielectric constant of the former. Further, studies on the temperature dependence of conductivity show that the enhanced conductivity passes through a peak at the respective T_c's, where the dielectric constant of the dispersed ferroelectric is highest i.e. at 30 °C and 90 °C respectively for composites containing BST 30 or BST 90 as dispersoid.

This paper deals recent studies on molecular design and utilization of boron compounds in polymer electrolytes. Well designed boron compounds have been used as dissociative lithium salts or anion receptors for enhancement of ionic conductivity and lithium ion transference number. Boron-containing polymers have not only anion trapping ability but also improving effects on properties of interface between electrolytes and electrodes. Special ion conduction phenomena in polymer electrolytes have been found using insoluble lithium orthoborates or a boric ester with crown ether substituents. Relationships between structures of boron compounds and properties of polymer electrolytes are discussed, and future directions of investigation on boron compounds for high-performance polymer electrolytes are outlined.

In the present study the nano sized TiO₂ has been dispersed into the gel polymer electrolyte 70PVAc:20DMF:10LiClO₄ at different concentrations by solution casting technique. XRD results reveal the dispersion of rutile phase nanoTiO₂ filler particles in the gel polymer matrix. The FTIR spectra show the interaction of Li⁺ ion with the ester and carbonyl oxygens of PVAc and also with TiO₂. The ac impedance analysis reveals the distribution of relaxation time in all the compositions of composite polymer matrix. The conductivity of 70:20:10 (PVAc:DMF:LiClO₄) gel polymer electrolyte has been found to be 2.53 × 10⁻⁵ Scm⁻¹ which increases to the maximum of 3.23×10⁻⁴ Scm⁻¹ with the dispersion of 15 m% TiO₂ filler at ambient temperature.

The validity of the extended version of Beer's Law, that the integrated absorption of the δ_s(CF₃) mode in PEO:LiCF₃SO₃ is independent of CF₃SO₃⁻ ion association, is tested and found to be valid. An infrared absorption marker, AsF6− is found to be effective for the quantitative comparison of absorption intensity in different samples.

Ionic transport in usual polymer electrolytes involves both cations and anions. In order to separate their respective contributions, cationic (Li⁺, Na⁺, K⁺), or anionic (Cl⁻, Br⁻, I⁻, BF₄⁻, (CF₃SO₂)₂N⁻) single-ion conducting ionomers (t₊ or t₋ = 1) were synthesized. In both cases, the counter ion is grafted to the macromolecular skeleton in the same synthesis step of cross-linking of the polymer. Experimental results for conductivity variations as a function of pressure (1 - 5000 bar) and temperature (20 - 140° C) show a great similarity for cationic and anionic ionomers. To interpret qualitatively the experimental results, a microscopic model is proposed. Charge carriers formation would result from the dissociation of the grafted salts. Their mobility would proceed by a “free volume” mechanism. This model introduces two local variations in volume, namely the local variation of volume associated with the dissociation process and the critical free volume necessary for the ionic migration. The interpretation of our results according to this model shows that the volume associated to the dissociation process is negative and can be attributed to a local reorganisation of the macromolecular chains around the dissociated charged species. The critical tree volume for ionic migration is positive and larger than the “dry” ionic volume, confirming the participation of the polymer chain segments in the ionic transport.

Polyurethane gel electrolytes with various solvents such as propylene carbonate (PC), propylene carbonate – ethylene carbonate (PC-EC) and γ-butyrolactone – ethylene carbonate (GBL-EC) were synthesized and studied by different characterization tools. Impedance spectroscopy and nuclear magnetic resonance spectroscopy (NMR) provides the insight on ionic mobility in the gel electrolyte. The syneresis effect was studied by observing the weight loss as a function of time. Morphology of the gel electrolyte was investigated by ESEM. Among the various compositions, the maximum conductivity was observed for 35%PU-60%EC/GBL-5%LiClO₄. The maximum conductivity of gel electrolytes was found to be 3.98 × 10⁻³ S/cm at the room temperature, which is higher than that reported in the domain of published literature for the thermoplastic polyurethane family. Moreover, merely 3.5% weight loss was observed for the period of 30 days. The 3.5% wt solvent loss has negligible effect on the conductivity of the gel electrolyte. Test cell was fabricated using polyurethane gel electrolyte and discharge characteristic was studied.

The wide scattering of experimental data shows unambiguously that Nafion^®117 conductivity is very sensitive to climatic conditions, temperature and relative humidity. Conductivity measurements have been carried out by impedance spectroscopy between 10°C to 95°C in abroad domain of relative humidity i.e. 10 to 98%RH. These accurate data enable a power relationship to be proposed at constant temperature between conductivity and relative humidity. This suggests that the solvation process of a sulfonic group involves four water molecules. Assuming a protonic mobility weakly dependent on temperature, a solvation enthalpy of a perfluorosulfonic acid group by water of −135 kJ·mol⁻¹ is deduced from conductivity variations with the temperature.

Efforts have been made here to develop a proton conducting composite polymeric gel electrolyte, namely, PEG-PVA-(NH₄CH₂CO₂)₂ system and investigate its ion conducting behavior. The gel samples with varying PVA concentration have been prepared in 1 M solution of (NH₄CH₂CO₂)₂ in Dimethyl Sulphoxide used as casting solvent. The XRD of samples exhibit crystalline nature of composite gel electrolytes which increases with increase of PVA concentration in the gel .Shift in endothermic transitions of constituents and corresponding broadness in DSC thermograms of as synthesized samples have been attributed to the formation of composite gel electrolytes. The room temperature ionic conductivity of gel electrolytes (3.5×10⁻⁴ S. cm⁻¹)have been found to be comparable to that of liquid electrolytes(5.52×10⁻⁴ S. cm⁻¹). Temperature dependence studies of ionic conductivity reflects VTF character of gel electrolytes

Chemically crosslinked composite membranes consisting of poly(vinyl alcohol) (PVA) and silicotungstic acid (STA) have been prepared by solution casting method and evaluated as proton conducting polymer electrolytes. The proton conductivity of the membranes were investigated as a function of blending composition, crosslinking density and temperature. The conductivity mechanism was investigated by using Impedance spectroscopy in the region between 40 Hz and 10 MHz. Membranes were also characterized by FTIR spectroscopy to confirm the crosslinking reaction and differential scanning calorimetry (DSC) to assess the thermal stability. Membrane swelling decreased with increase in crosslinking density accompanied by improvement in mechanical properties. The proton conductivity of the membranes were of the order of 10⁻³ S/cm and showed similar resistance to methanol permeability than Nafion 112 under the same measurement conditions.

A new polymer electrolyte, based on poly (ethylene oxide) complexed with Na₄P₂O₇ is investigated. (PEO)_n:Na₄P₂O₇ polymer metal salt complexes with different n = [ethylene oxide]/ Na ratio (80,100,120,160 and 200) are prepared by solution casting method. Dissolution of the salt into the polymer host is investigated by X-ray diffraction, differential calorimetry and Scanning electron microscopy techniques. The formation of the complex has been confirmed by (i) the broadening and reduction in the intensity of the Bragg peaks (ii) the reduction in the percentage of crystallinity by DSC and (iii) the increase in the glass transition temperature of the polymer with addition of the salt. Maximum reduction in crystallinity from 76.1 % to 56.2 % is observed for (PEO)₁₂₀:Na₄P₂O₇ system. Qualitative analysis of FTIR spectra in the range 3000-500 cm⁻¹, reveals broadening of the bands corresponding to the C-O-C symmetric stretching modes around 840 cm⁻¹ and 1057-1160 cm⁻¹. These conformal changes have inferred the coordination of the ether oxygen of the PEO with the metal salt ion. Compositional dependence of conductivity studies show a maximum value of 7.58 × 0⁻⁷ S/cm at 351 K for O:Na = 120.Conductivity of the above electrolytes proceeds via an activated conduction mechanism with two activation energies, 0.62 eV and 0.78 eV above and below the softening of the polymer. The electronic transport number measured by dc polarization technique shows that, the conducting species are ionic in nature.

Poly (vinyl chloride)(PVC)-based solid polymer electrolyte films with LiClO₄+plasticizer (dimethyl phthalate) have been prepared by the solution -cast technique. Various experimental techniques have been used, such as X-ray diffraction (XRD) and infrared spectroscopy (IR), a.c. impedance spectroscopy and transport number measurements, to characterize these polymer electrolyte films. The complexation has been confirmed from XRD and IR studies. A maximum room temperature conductivity (1.1 × 10⁻⁴S/cm) has been observed for (PVC+LiClO₄+DMP)(20:5:75) complex. The temperature dependent conductivity plots show Arrhenius behaviour. The activation energy is estimated and the results are discussed. The transference number data indicated that the conducting species in these electrolytes are the anions. Using this electrolyte, electrochemical cells are fabricated and their discharge profiles are studied under constant load.

The stability of the gel electrolyte consisting of polyacrylonitrile (PAN), ethylene carbonate (EC), propylene carbonate (PC) and lithium trifluoromethanesulfonate (LiCF₃SO₃ – LiTF) towards metallic lithium was investigated using the time evolution of impedance plots. Symmetric cells of the form Li / PAN : EC : PC: LiTF / Li were assembled and impedance data were collected at room temperature for one week. A clear indication of growth of a resistive layer could be seen. The electrolyte resistance remained constant. The growth of the passivation layer became constant after first two days. These observations suggest that this gel electrolyte is suitable for use with metallic lithium.

The solid polymer electrolyte systems, based on poly(ethylene oxide) (PEO) and lithium ions have attracted much attentions as a potential electrolyte medium in secondary energy sources and electrochromic devises. They show a characteristic property of an enhanced ionic conductivity when a plastizier is added. In this research work, PEO and lithium triflate have been taken as the electrolyte medium and an attempt was paid to improve the ionic conductivity of (PEO)₉LiCF₃SO₃ polymer electrolyte system by choosing montmorillonite (MMT) as the plastisizer. The ionic conductivity, thermal transitions, crystallinity, and bonding of the complex system of (PEO)₉LiCF₃SO₃ + x wt.% MMT (x = 0, 3, 4, 5, 6, 10, 15, 20) were systematically characterized by ac-impedance spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD) spectroscopy and fourier transformed infrared (FTIR) spectroscopy, respectively.

The ac-impedance data reveal that the ionic conductivity of (PEO)₉LiCF₃SO₃ system is changed with the concentration of MMT, maximum conductivity of 4.14857 × 10⁻⁷ S cm⁻¹ at room temperature was observed for the system of (PEO)₉LiCF₃SO₃ + 5 wt.% MMT. However, the ionic conductivity of the above system was increased with the increase of temperature, and the highest conductivity of 2.63 × 10⁻⁴ S cm⁻¹ was observed at 80°C. The DSC and XRD data clearly show that the crystalline nature of PEO is reduced when MMT is added. The glass transition temperature (−46.37°C) and melting temperature (53.72°C) of the above system is reduced compared to those of other systems. This supports to the conductivity enhancement in an amorphous environment.

The FTIR spectra obtained for MMT, PEO, (PEO)₉LiCF₃SO₃, and (PEO)₉LiCF₃SO₃ + 5 wt.% MMT clearly indicative that the interactions take place between these constituents, as the intensities of typical stretching vibrational modes of 916 cm⁻¹ ν (Al-O-H), 1040 cm⁻¹ ν (Si-O) and 3300-3700 cm⁻¹ ν (O-H) in MMT, and the vibrational modes of CH₂ rocking at 948 and 840 cm⁻¹ and C-O stretching at 1149 and 1090 cm⁻¹ in PEO are shifted. The change of symmetric bending mode of CF₃ [δ_s (CF₃)] at 752 cm⁻¹ in lithium triflate has altogether supported the bonding characteristics in the electrolyte system and the corresponding conductivity enhancements.

Three kinds of the polymer matrix, poly(ethylene oxide)-grafted polymethacrylate (PEO-PMA), poly(vinyldene fluoride) (PVdF) and poly(vinyldene-co-hexafluoropripylene) (PVdF-HFP), were used for gel preparation. A proper amount of organic salts or acids were dissolved in the polymer matrix together with organic plasticizers, dimethylformamide (DMF) and/or poly-(efhylene glycol)-dimethylether (PEGDE), without water. Thin films of the polymeric gel were obtained by either direct polymerization of the mixed monomer solution or a thermal casting method. The composition of the polymer-electrolyte complex system is optimized to obtain good capacitor performances of the electrochemical capacitor (ECC) system.

Proton conducting polymer electrolytes based on Poly (vinyl acetate) (PVAc) and perchloric acid (HClO₄) has been prepared by solution casting technique with various compositions. FTIR spectra analysis reveals the interaction between proton and ester oxygen of Poly (vinyl acetate) (PVAc). Ac impedance spectroscopy reveals that 75m%PVAc:25m%HClO₄ exhibits maximum conductivity, 6.2×10⁻² Scm⁻¹ at room temperature (303K). The increase in conductivity with increase in dopant concentration and temperature may be attributed to the enhanced mobility of the polymer chains, number of charge carriers and rotations of side chains. The temperature dependence of conductivity shows non-arrhenius behaviour at higher temperatures. Dielectric loss spectra show two relaxations α (high temperature) and β (low temperature) relaxations in low and high frequency range respectively

Poly (ethylene oxide)-(PEO)-based composite polymer electrolytes are of great interest for solid-state-electrochemical devices. This paper presents the results of a preliminary study on electrical conductivity and thermal behavior (DSC) of composite polymer electrolytes (CPEs) containing PEO: LiCF₃SO₃ complexed with plasticizer (EC) and incorporating nano-sized particles of the ceramic filler Al₂O₃. Ionic conductivity enhancement in these electrolytes has been obtained by optimizing the combined effect of the plasticizer and the ceramic filler. Nano-composite, plasticized polymer electrolyte films (400-600μm) were prepared by common solvent casting method. It was revealed that the presence of the Al₂O₃ filler in PEO: LiTf polymer electrolyte significantly enhanced the ionic conductivity in the temperature range of interest, giving the maximum conductivity for (PEO)₉LiTf+15 wt.% Al₂O₃ CPE [σ_RT (max)=2×10⁻⁵ S cm⁻¹]. It was also observed that the addition of plasticizer (EC) to this electrolyte up to a concentration of 50 wt. % EC, showed a further conductivity enhancement [σ_RT (max) = 1.5×10⁻⁴ S cm⁻¹]. It is suggested that the conductivity is enhanced mainly by two mechanisms. The plasticizer (EC) would directly contribute by reducing the crystallinity and increasing the amorphous phase content of the polymer electrolytes. The ceramic filler (Al₂O₃) would contribute to conductivity enhancement by creating additional sites to migrating ionic species through transient bonding with O/OH groups in the filler surface. The decrease of T_g values of plasticized CPE systems seen in the DSC thermograms points towards the improved segmental flexibility of polymer chains, increasing the mobility of conducting ions.

Biomaterial has occupied leading position in material science for various scientific and technological applications. This present work is carried out over a natural gum extracted from raw fruit of Mangosteen, an east Indian tree (Gercinia Mangostana) following extraction and purification process. Solid specimen of the said gum is developed following sol-gel like process.

AC and DC electrical analysis on the dried solid specimen of the gum were carried out and showed high electrical conduction with σ ~ 1 E-03 S/cm, of which ionic and electronic contributions are 70% and 30% respectively. Analysis shows that origin of high electrical conductivity is due to presence of substantial amount of organic acid unit in its polysaccharide background. In fact the observed σ is about 1000 times of that observed in gum Arabica. Optical absorption of this new bio- materials are also studied using UV-VIS analysis. The results show its high absorption co-efficient in UV and blue part of analysed range. A complete electrical characterization of the material have been made. It has also been observed that the electronic conduction can be enhanced to 70% of the total electrical conductivity by forming complex with Iodine and organic (Citric) acid from Lemon fruit. This high potential material is being studied for development of electronic device application.

Novel solid polymeric electrolyte (SPE) consisting of Poly (ethylene oxide) PEO with magnesium chloride as the electrolyte salt has been prepared by solution casting technique. Measurements with differential scanning calorimetry (DSC) indicates the modification of PEO crystalline structure with increasing content of magnesium salt up to 20 wt% and increase in crystallinity at higher concentration. FTIR studies indicates the interaction of Mg cations with ether oxygen of PEO, Ionic conductivity increases with increase in salt content, and it is optimized at 20 wt% Mg salt. The decrease in ionic conductivity at higher salt content above 20 wt% is due to ion-ion interaction, which leads to ion pair formation and increase in relative crystallanity fraction due to recrystallization above 15wt%.

The proton conducting solid polymer electrolytes comprising of partially hydrolyzed Poly (vinyl alcohol) and Ammonium thiocyanate have been prepared at different composition by solution cast method. The solid polymer electrolytes have been subjected to ¹H NMR, Raman and AC impedance spectroscopy analysis. Raman analysis confirms the amorphous nature and complexation of solid polymer electrolytes. Raman studies also provide the details about aggregation of ions in the polymer electrolyte system. ¹H NMR analysis indicates that the observed chemical shift at 6.3 ppm is due to NH₄⁺ ion. It is also observed that the intensity of the peak at 6.3 ppm is maximum for 15 mol% NH₄SCN doped polymer electrolyte which indicates the free NH₄⁺ ions is maximum for this concentration. This result is consistent with conductivity data which indicates the maximum conductivity at 15 mol% NH₄SCN doped polymer electrolyte and ionic conductivity has been found to be 3 × 10⁻³ S cm⁻¹. The temperature dependent ¹H NMR studies indicate that the acetate ion which is the residual part of partially hydrolyzed PVA also involved in the conduction process. The ¹H NMR also confirms that the mobile species in the polymer electrolytes are NH₄⁺ ion.

Solid polymer electrolytes comprising polyethylene oxide (PEO), silver triflate (AgCF₃SO₃) and varying weight percentage of Al₂O₃ (0, 2, 5, 10, 15) nanoparticles, were prepared by solution casting technique using acetonitrile as the common solvent. These polymer electrolytes were formed as very thin films of large surface area and the thickness of these films was measured using Air-Wedge technique. Typical values for the thickness of these films ranged from 30 to 100 μm. The effect of the dispersion of various amounts of Al₂O₃ nanoparticles in polyethylene oxide - silver triflate polymer electrolytes was characterized by X-ray diffraction (XRD), Differential scanning calorimetry (DSC) and Wagner's polarization techniques. The X-ray diffraction pattern, indicated the amorphous nature of the polymer electrolyte. The DSC traces showed slight change in the glass transition temperature (T_g), whereas the degree of crystallization (X_c) decreased from 99.2%(pure PEO) to 27.3% for the nano - Al₂O₃ blended polymer electrolytes. The total ionic transference number (t_ion) calculated by wagner's polarization technique was found to be approximately unity, reveling that the significant contribution to electrical conduction was due to ions.

One of the most promising ways to improve the potential for applications of plasticizer-free, PEO – based solid polymer electrolytes is through the incorporation of ceramic fillers. However, to our knowledge, literature on PEO₉ LiTf reporting the dependence of ionic conductivity on the nature of different types of ceramic fillers is lacking. In this work, we have studied thermal and transport properties of the polymer electrolyte PEO₉ LiTf + 15 wt% filler, incorporating four different types of ceramic fillers TiO₂, Al₂O₃, ZrO₂ and BaTiO₃. Presence of the first three ceramic fillers with dielectric constants 435, 20 and 12.5 enhanced the ionic conductivity substantially. However BaTiO₃ filler having a relatively very high dielectric constant (3000) compared to other three ceramic fillers, gave a negative effect on conductivity. Presence of 15 wt% TiO₂ exhibited the maximum enhancement in conductivity (σ_RT = 4.2 × 10⁻⁴Scm⁻¹) The observed conductivity enhancement has been attributed to Lewis acid-base type surface interactions of ionic species with O/OH groups on the filler surface.

Polymer electrolytes based on poly (vinyl pyrrolidone) - ammonium thiocyanate have beeri prepared by solution cast technique. The interaction of salt with the polymer has been examined using Raman spectroscopy. Results revealed that the interaction of the salt has been found to be through the carbonyl group of the polymer matrix. Conductivity measurements showed that these systems conduct ionically. The possible correlation between the conductivity and the structure of these electrolytic systems was also investigated which shows that the conductivity values are directly related to the total “free anion” concentration. Conductivity analysis showed that the addition of ammonium thiocyanate as a dopant in the polymeric electrolyte system enhanced the ionic conductivity. 20 mol% ammonium thiocyanate doped polymer electrolyte exhibits high ionic conductivity and has been found to be 1.7 × 10⁻⁴ S cm⁻¹, at room temperature.

A new polymer gel electrolyte system consisting of polyvinylidene fluoride (PVDF) and silver triflate (AgCF₃SO₃) has been investigated and reported in the present work. Thin film specimens of PVDF + x wt.% AgCF₃SO₃ (where x = 10, 20, 30, 40, 45, 50, 55 and 60 respectively) were prepared by solution casting technique using dimethyl formamide (DMF) as the common solvent. Complex impedance measurements were carried out on all the specimens in the frequency range 20 Hz – 1 M Hz within the temperature domain 298 to 333 K. The room temperature ionic conductivity of the polymer electrolyte was found to increase from 10⁻⁵ to 10⁻³ Scm⁻¹ i.e. by two orders of magnitude with increasing concentration of silver triflate from 10 to 60 wt.%, whereas the activation energy decreased with an increase in concentration of the dopant salt. The ionic transference number values determined by Wagner's polarization technique showed an increase from 0.33 to 0.99 with an increase in the concentration of silver triflate salt. These results have clearly indicated that the ionic conduction is significant in the case of higher salt concentrations viz., > 20 wt.%. Furthermore, the X-ray diffraction (XRD) patterns have revealed a decrease in the crystallinity of the polymer electrolyte due to complex formation. Fourier transform infrared (FTIR) spectral studies have also confirmed the complex formation between polyvinylidene fluoride and silver triflate owing to the appearance of new absorption bands and gradual shifts observed in certain peaks.

The polymer electrolytes composed of Poly (vinyl acetate) (PVAc) with various stoichiometric ratios of lithium perchlorate (LiClO₄) salt have been prepared by solution casting method. The techniques Fourier Transform Infra-red (FTIR) and micro Raman spectroscopy have been used to study polymer- salt complex formation, ion-ion and ion-polymer interactions as a function of salt concentration The ac impedance results show the depressed semicircles which indicate the non-Debye nature of the polymer electrolytes. The maximum ionic conductivity has been found to be 1.3×10⁻³ Scm⁻¹ at 373K for the 80PVAc:20LiClO₄ polymer complex. The ⁷Li NMR linewidth decreases with increasing temperature which indicates the enhancement of lithium ion mobility in the polymer electrolytes. The two different environments of Li⁺ ion in the polymer electrolytes observed in ⁷Li NMR have been confirmed by FTIR analysis.

In the present study, PVA based solid polymer electrolyte films complexed with NaSCN at different salt concentration have been prepared by the solution cast technique. This PVA-NaSCN polymer electrolyte has been characterized by FTIR and ac impedance spectroscopy techniques. The FTIR study confirms the polymer-salt complex formation. The temperature dependant conductivity of the polymer electrolyte follows the Arrhenius relationship. It has been observed that the conductivity increases with increasing salt concentration for all temperatures. The maximum conductivity has been found to be 3.28×10⁻³ Scm⁻¹ at 303K for 20 mol% of NaSCN doped electrolyte. The dielectric spectra, modulus spectra and dielectric loss tangent have also been analyzed.

Poly (ethylene oxide) PEO based polymer electrolyte films were prepared by solution casting method by incorporating PEG -2000 as plasticizers. To find out the effect of fillers in the plasticized system TiO₂ is added. The interactions between filler, plasticizers and PEO chains are studied by Differential Scanning Calorimeter (DSC) and FT-IR techniques. Effects of filler and plasticizers on the properties of the PEO-based electrolyte, such as ionic conductivity and thermal behavior are studied. The ionic conductivity of the plasticized system does not found to change much with the addition of filler.

Conducting polymer bilayers with poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy), each containing dodecyl benzenesulfonate (DBS) as immobile dopant species, were synthesized galvanostatically. The electrochemical behaviour of the bilayers was investigated using cyclic voltammetry, optical absorption spectroscopy and electrochemical quartz crystal microbalance (EQCM) techniques. Two important conclusions of relevance for actuator performance were reached: It is possible to make a bilayer film that does not delaminate – the two polymers are compatible; and both polymers are active in the redox process as ions are able to move through the PEDOT layer and penetrate into PPy.

The nanocomposite films are prepared from a V₂O₅ sol and aniline by sol-gel method, followed by anode electrophoresis deposition (EDP), and characterized by IR and NMR, cyclic voltammetry and ac-impedance spectroscopy, etc. IR spectroscopy and NMR results demonstrate the presence of PANI in its emeraldine salt form, as the xerogel is formed by negatively charged ribbons, V₂O₅ act as a counterion to compensate the positive charge present on the nitrogen atoms. Electrochemical impedance data at −0.7 V show that the Li⁺ diffusion coefficient in the (PANI)_0.51·V₂O₅·1.30H₂O film is 2.92×10⁻¹¹ cm²·s⁻¹, in contrast to the value of 5.10×10⁻¹² cm²·s⁻¹ obtained for V₂O₅ and the electronic conductivity of the nanocomposite increases compared to V₂O₅.

Due to lack of good proton conductive polymer electrolyte working at ambient temperatures, search for the new systems have been hotly pursued in the past few years. Hence an attempt has been made to synthesis PVA based polymer electrolyte with various compositions of ammonium nitrate using solution casting technique. The formation of the complex has been confirmed by FT-IR spectral studies and XRD analysis. In the impedance response curve, the absence of the high frequency semicircular portion leads to the conclusion that the current carriers are ions & therefore the total conductivity is mainly the result of ion conduction. The high ionic conductivity at ambient temperature is found to be 7.5×10⁻³ Scm⁻¹ for 20mol% ammonium nitrate doped PVA. Dielectric behaviour is analyzed using dielectric constant(ɛ') and dielectric loss (ɛ") of the samples .The low frequency dispersion of the dielectric constant implies the space charge effects arising from the electrodes. The dielectric loss spectra show the very large (~10⁶) dielectric loss at lower frequencies due to free charge motion within the material.

A systematic investigation has been carried out in PVA complexed with potassium thiocyanate prepared by solution cast technique. This PVA-KSCN polymer electrolyte has been characterized by FTIR and ac impedance spectroscopy techniques. The temperature dependant conductivity of the polymer electrolyte follows the Arrhenius relationship. The maximum conductivity has been found to be 1.63×10⁻³ Scm⁻¹ for 15 mol% KSCN doped electrolyte at 303K. It has been observed in the loss tangent spectra as the frequency increases, relaxation peak shift towards higher temperature region showing that the relaxation frequency increases with temperature. The appearance of two sets of relaxation peaks indicates that the system shows two different types of relaxation process having different relaxation times.

Electrolyte materials used in solid state polymer batteries can also be utilised in a special type of drug delivery system called an iontophoretic device. This review will describe the history, applications and limitations of iontophoretic and related systems and also the use of batteries and biofuel cells in medicine.

The present lithium ion battery technology is based on liquid organic electrolytes, which have several disadvantages and severe problems. These are related to safety concerns because of potential electronic short circuits of the electrodes, formation of reaction product layers at the interfaces (“solid electrolyte interfaces, SEIs”), leakage of the liquid, low electrochemical decomposition voltages and flammability of the electrolyte, and accordingly restrictions with regard to higher energy densities. Solid electrolytes may provide solutions to the problems. However, so far all discovered compounds had either high ionic conductivity or high electrochemical stability, but not both. In addition, some of the compounds became predominantly electronic conductors, e.g., (Li,La)TiO₃, within the lithium activity range given by the cathode and anode. Furthermore, since polycrystalline materials are being used for practical applications, large grain boundary resistances are commonly observed in addition to the bulk resistance and therefore control the total cell resistance.

Here, we report predominant ionic conduction in garnet-type structures of the general composition Li₆ALa₂M₂O₁₂ (M = Ta, Nb; A = Sr, Ba) and we show that these materials overcome the existing problems. The tantalum compounds are stable against reaction with molten elemental lithium, have high decomposition voltages, which allow application of the highest energy density cathodes, and exhibit fast 3-dimensional lithium ion conductivity similar to that of the best (but unstable) known solid electrolytes. Furthermore, the grain boundary resistance is negligible compared to that of the bulk.

Thin film all-solid-state lithium batteries have been made on the basis of chemically and electrochemically stable solid electrolytes with high voltage intercalation type cathodes and aluminium as anode in the discharged state.

Intermediate temperature solid oxide fuel cells have attracted considerable attention due to their good performance at relatively low operating temperatures, 450 – 650°C. This temperature range is favourable for many reasons, the temperature is high enough for efficient catalysis, still low enough to avoid problems associated with high temperature operation. Reversible fuel cells may operate as regular fuel cells as well as electrolysers and are therefore an interesting option in applications where the demand and surplus of energy is alternating, as for example, in solar energy plants. The possibilities to use reversible intermediate temperature solid oxide fuel cells using ceria-based electrolytes are reported in this paper.

Apart from the reduced scale of transport lengths, enhanced surface-to-volume ratio in nano-crystals lead to a variety of exciting phenomena in the field of nano-ionics. We consider here some of those with special emphasis in the context of lithium batteries, addressing anomalies in thermodynamic, transport and storage properties: (a) Nanocrystallinity does not only lead to modifications in the cell voltage typically ≤ 100 mV due to Gibbs-Kelvin term in the chemical potential, it also affects the shape (no longer necessarily plateau) of the discharge curves in a lithium battery. (b) Nanocrystallinity also allows for a storage anomaly. RuO₂ and IrO₂ electrode materials, exhibit a high storage capacity (600 - 1130 mA h g⁻¹) with nearly 100% Columbic efficiency at the first discharge/charge cycles. (c) Nano-sized rutile exhibits remarkable electrochemical performance in up-taking 0.8 Li⁺ per TiO₂ as compared to bulk rutile (which incorporates only about 0.1 - 0.25 Li⁺) and showing excellent capacity retention and rate performance. (d) Apart from the enhanced storage capacity and efficiency, another important feature of nanocrystallinity is “Heterogeneous interfacial storage” explaining extra Li storage at low potential. Here, we briefly present both the experimental and theoretical results supporting this interfacial storage mechanism.

Electrochromic (EC) materials are able to change their optical properties, persistently and reversibly, under insertion/extraction of ions and electrons. When integrated in solid state devices, they can be used for a variety of applications such as energy efficient “smart windows” in buildings and vehicles, visors and goggles, displays, etc. This paper summarizes some recent work with special emphasis on nano features of EC materials and devices.

Gas sensors has been currently in great demand due to serious concern over environmental pollution and public health considerations resulting from tremendous growth of industrialization. Concurrently, there have been continuous efforts to obtain sensors with improved performance. This article presents the factors contributing towards a gradual development of electrochemical solid-state gas sensors in terms of a continuous tailoring of its two basic components i. e., solid electrolyte and reference electrode. Particularly, the conductivity data of optimized carbonate based solid electrolytes indicated about three orders of magnitude enhancement in conductivity due to glass dispersion. The sensor performance of glass as well as ferroelectric dispersed composite electrolytes is better than mono-phase.

Some conjugated polymers can convert electrical energy to mechanical energy (via chemical energy), thereby acting as electro-chemo-mechanical actuators or “artificial muscles”. The advantage of this type of actuator is that the process can be driven by the application of a small potential (1-5 V), opening the possibility of making control and measurement both safe and accurate. The actuation process is identical to charging and discharging an electrochemical cell during redox cycling of a rechargeable battery. It involves ions moving between the electrolyte and being inserted in, or expelled from the matrix of a polymer electrode – thereby causing volume expansion which can be converted into work. Solvent molecules are able to penetrate the polymer too. A precise description of the nature of these ionic and solvent movements is therefore important for understanding and improving the performance. This work examines the influence of solvent, ionic species and electrolyte concentration on the fundamental question about the ionic mechanism involved: Is the actuation process driven by anion motion, cation motion, or a mixture of the two? In addition: What is the extent of solvent motion? The discussion is centered on polypyrrole (PPy), which is the material most used and studied. The tetraethyl ammonium cation (TEA) is shown to be able to move in and out of PPy(DBS) polymer films, in contrast to expectations. There is a switching between ionic mechanisms during cycling in TEACl electrolyte.

Conducting polymers have high potential for FRET. The development of Light Emitting Diodes (LED) has taken place at quite a fast pace due to their nontoxic, easy processing and low cost development techniques. The LEDs based on conducting polymers are mechanically flexible and strong. However, the commercialization of these devices has not yet been made. During the work on the development of conducting polymer based (MEH-PPV) LED, we have identified four problems which have to be taken care of before the device fabrication:

a) To maintain a balance between electron and hole concentrations one has to use a composite structure of two polymers one a hole transporting layer (HTL) and other a electron transporting layer (ETL). To use a single layer of emissive polymers is not desirable.

b) The thickness of ETL must be optimized so that the recombination of injected electrons and holes takes place near the cathode; the exciton will break due to high electron affinity of ETL resulting in the loss of electro luminescence (EL). On the other hand if the recombination takes place near anode, the exciton will again break due to high ionization potential of HTL.

c) The work function of the cathode should be as low as possible so that the potential barrier for electron injection at the cathode is low. To use buffer layers of material such as LiF, K or Ba with optimized thickness between the ETL and Al cathode contacts is a possible solution.

The mobility of the injected carriers should be as high as possible. For this the morphology of the films should be improved by optimizing the concentration of the solute before spin coating the film on the ITO coated glass substrates. The speed and duration of spin coating should also be optimized.

No abstract received.

SrCeO₃, SrCe_1−xM_xO₃ compositions were synthesized by sonochemical treatment followed hydrothermal method and sintering is done by microwave heating. CeO₂ hydrated gel was obtained from Ce(IV) ammonium nitrate and mixed with Sr(OH)₂ and sonicated for 30 min., then the reactants were subjected to hydrothermal treatment at 150°C for 4 h. SrCeO₃ was found to form orthorhombic perovskite above 1200°C of heat-treatment. The powders were characterized by XRD, TEM, and EIS techniques. The effect of ball milling was also studied on sintering of the pellets. The 10% substitution of dysprosium at Ce site does not form single phase. Instead Sr₂CeO₄ is formed along with SrCeO₃. Similarly, Eu, Er (10 % and 90 %Ce) were also attempted to substitute at Ce site; however, SrCe_1−xM_xO₃ (x=0.10) does not take up 10 % substitution. The electrical conductivity measurements were carried out on the single phase pellets by ac impedance techniques. The results of the experimental results obtained in this study are discussed in this paper.

Various compositions of ceria, Gd-doped ceria and perovskite such as Sr−, Mg− doped LaGaO₃, Sr-doped LaMnO₃, Sr-doped lanthanum ferrate, cobaltate, LaCrO₃ and doped compositions were prepared by adopting several preparation methods. The materials were tailored to be used as anode, cathode, and electrolyte and interconnect in solid oxide fuel cells (SOFCs). The materials were characterized by XRD, TEM and other spectrochemical methods. Electrical conductivity of the compositions was measured by electrochemical impedance spectroscopy (EIS). These experiments were carried out to optimize the composition and various properties of the materials to be used in natural gas fuelled SOFCs. The study is aimed at developing materials to fabricate natural gas fueled SOFC hybridized to a gas turbine (SOFC-GT) to enhance power production and maximum utilization of resources in Trinidad.

A typical solid oxide fuel cell (SOFC) consists of an oxygen-ion conducting solid-electrolyte, usually yttria-stabilized zirconia (YSZ), and electrodes deposited on two sides of electrolyte. The SOFC usually operates between 800-1000 □. The high operating temperature is due to the low oxygen-ion conductivity of the electrolyte at low temperature and also due to slow electrode kinetics. In this study, we made a SOFC using GDC (Gd₂O₃-doped CeO₂) thin film on nano-porous substrate. Anodic nano-porous alumina membrane has been employed as a substrate. The substrate has nanometer-size columnar pores (200nm) which penetrate the substrate vertically. Porous Pt thin-film as an anode was deposited onto the substrate by DC sputtering. On top of Pt anode, dense GDC thin film (∼2μm) was deposited by pulsed laser deposition. To measure the resistance of GDC and the open-circuit voltage (OCV) of cell, another Pt electrode as a cathode was painted on the surface of GDC thin film. Substantial OCV was developed when humidified H₂ gas was flown over anode below ∼500□. However, the measured OCV was lower than the theoretical OCV due to low activity of Pt electrode. The enhanced OCV will be expected when highly active electrodes were used

The demand for compact and high energy density batteries is constantly increasing with miniaturization of micro batteries for portable devices. All solid state batteries that consist of solid electrolyte and two electrodes have attracted much attention, because of their potential for flexibility, safety and further miniaturization. Superionic glass AgI-AgPO₃ is well known superionic conductor that has been investigated by many different techniques. Its high conductivity up to ~ 10⁻² S/cm at ambient temperature has attracted many researchers to understand the mechanism of ionic conductivity. The neutron scattering studies revealed the existence of prepeak at low Q in the structure factor S(Q) and the boson peak at low energy in the dynamic structure factor S(Q,E). Those results showed that many interesting phenomena were found out in this material. However, its application as solid electrolyte in a solid state rechargeable battery is only little known. In order to complete the feature of this material, we fabricated cell batteries Ag/ AgI-AgPO₃ /I₂,C . The silver and iodine-carbon were used as the anode and cathode, respectively. This paper will describe the recent results of solid electrolyte AgI-AgPO₃ and the performance of the new solid state battery.

The performance of lithium polymer cells fabricated with Polyacrylonitrile (PAN) based electrolytes was studied using cycling voltammetry and continuous charge discharge cycling. The electrolytes consisted of PAN, ethylene carbonate (EC), propylene carbonate (PC) and lithium trifluoromethanesulfonate (LiCF₃SO₃ – LiTF). The polymer electrode material was polypyrrole (PPy) doped with dodecyl benzene sulfonate (DBS). The cells were of the form, Li / PAN : EC : PC : LiCF₃SO₃ / PPy : DBS. Polymer electrodes of three different thicknesses were studied using cycling at different scan rates. All cells had open circuit voltages in the range, 3.0 – 3.5 V vs Li. With increasing scan rates as well as thickness of the polymer electrode, diminishing of peaks and increase of peak separation in cyclic voltammograms was seen. Charge values obtained with constant charge discharge cycling and with cyclic voltammetry at slow scan rates were similar. The charge factor remained close to unity. These results show the fact that satisfactory cell performance can be achieved with thin electrode films and cycling at slow scan rates.

Molybdenum trioxide nanobelts have been synthesized via the simple hydrothermal reaction by using MoO₃ sols as precursor. The morphology and structure of the samples were characterized by XRD, SEM and TEM. The results indicate that the samples are α-MoO₃ nanobelts with the thickness of 20∼70 nm and with length up to 10 μm, and the nanobelts are single crystals elongated preferentially in the [001] direction. The effect of different reaction time on the structure and morphology of the samples and the growth mechanism for MoO₃ nanobelts have been studied. The electrochemical properties of the MoO₃ nanobelts have been investigated finding that Li⁺ ions showed better reversibly insertion/extraction cycles in as-synthesized MoO₃ nanobelts than in bulk MoO₃ samples.

The electrochemical behaviour of Li rechargeable cells with Polypyrrole (PPy) as the cathode material was investigated using cyclic voltammetry. The PPy used was doped with the large surfactant anion dodecyl benzenesulphonate (DBS). The cells were constructed with PAN:LiTF:EC:PC gel electrolyte with Li as anode. The results indicate that during the first reduction, cations are inserted into the PPy film forming LiDBS neutral salt. During the next oxidation/reduction cycles, the mechanism then switches to anion movement. Cyclic voltammetry studies also verified that complete electrochemical reversibility could be obtained at very low sweep rates.

Potentiometric devices were fabricated using a NASICON (Na_1+xZr₂Si_xP3_−xO₁₂) thick film and auxiliary layers. The powder of a precursor of NASICON with high purity was synthesized using the sol-gel method. Using the NASICON paste, an electrolyte was prepared on the alumina substrate through screen printing and then sintered at 1,000°C for 4 hours. In the present study, a series of Li₂CO₃-CaCO₃ system was deposited on the Pt sensing electrode. Within a wide range of CO₂ volume ratio concentration from 1,000 ppm to 10,000 ppm, the output of the sensor showed good electromotive force (EMF) response that was very close to the theoretical value. The device to which Li₂CO₃-CaCO₃ (1:2) was attached showed good sensing properties at low temperatures.

Solid-state batteries have been fabricated with the cell configuration: Anode//0.9[0.75AgI: 0.25AgCl]: 0.1TiO₂, (OCC) // Cathode. Ag-metal was used as anode while different cathodes material such as mixture of elemental iodine & carbon powder (i.e. C+I₂) in 1:1 wt% ratio and mixture of elemental iodine, carbon powder & electrolyte (i.e. C+I₂+ electrolyte) in 5:5:1 wt% ratio were used The solid-state batteries discharge characteristic studies have been carried out under different load conditions. Cell parameters viz. current density, power density: discharge capacity and energy density were evaluated and reported. The transference number (t_ion-I) has also been measured for the composite electrolyte systems using electrochemical cell potential technique which is identical to the value reported earlier by TIC technique for the composite system. The battery was fabricated using (C+I₂+electrolytes) as a cathode materials, it shows higher stability for long time (~300 hours) at high load resistance as compare to cell fabricated using (C+I₂) as a cathode material.

The protonic solid-state batteries with different intercalating cathodes such as MnO₂, PbO₂ and V₂O₅ were fabricated using composite zinc as an anode and montmorillonite (Al₂O₃.4SiO₂.H₂O.xH₂O) as solid electrolyte. The discharge profile of these electrochemical cells, in series and parallel combinations, was recorded at constant current drain. Proton transference number, which determines efficiency of electrochemical cells, evaluated by EMF method was found to be ~ 0.90 with very negligible electronic contribution. The battery with MnO₂ as cathode exhibits maximum energy density and low internal impedance amongst all.

We report on a novel synthetic method of microwave processing with a domestic 2450MHz microwave synthesis system to prepare ZnO fiber using pure ZnO powder. We also studied and report on structure and morphology of the resultant products by XRD and SEM. XRD revealed that a single phase ZnO fiber can be synthesized quickly and easily by microwave processing. The results indicate that microwave processing is a promising method of processing ZnO fiber.

Sn is a material that is essentially insoluble in Ge and Si in the bulk form. In this study, Sn/Ge and Sn/Si powders were ball milled for long durations (~36 hrs.) while varying the ratio of Sn to Ge and Si respectively. Milling was carried out in an Ar gas atmosphere. Analysis made using XRD showed that the particle sizes of Ge and Si go down with the decreasing atomic composition of Sn. Particle size estimated using x-ray diffraction line broadening showed that the sizes of Ge and Si particles in Sn/Ge and Sn/Si samples with 20% vol. Sn in Ge and 10% vol. Sn in Si reach nano-scale dimensions. Analysis made using X-ray Absorption Fine Structure Spectroscopy (XAFS) showed that there were surface layers of SnGe and SnSi alloys around Ge and Si particles. Thus ball milling of Sn/Ge and Sn/Si powders produces SnGe alloy coated Ge nanoparticles and SnSi alloy coated Si nano particles.

The fine powder of TiO₂ has been synthesized by totally alkoxide free sol gel method. The ammonium citratoperoxotitanate (IV) has been synthesized and used as molecular precursor which is highly stable in air. This starting precursor allows us to avoid the use of titanium alkoxide or titanium tetrachloride, which are extensively reported in literature. The synthesis has been carried out in ambient atmospheric conditions. The modified polymerizable precursor method has been adopted for the sol gel chemistry of TiO₂. The final powder precursor has been analysed by thermal analysis (TG and DTA) to explore the thermal kinetics. The X-ray diffraction analysis through Rietvield method confirms that the final product is highly pure rutile TiO₂ powder. The laser granulometry and SEM analysis show the agglomeration of fine particles with size in the order of 200 nm.

The development of polymer-fullerene plastic solar cells has made significant progress in recent years. The quality of the device depends on the efficiency of the photoinduced charge generation and on how fast these charges are separated so that the excitons are not able to decay radiatively to ground state emitting photoluminescence. For the excitons to be broken into free charge carriers and for their fast collection it is necessary to use a composite structure of the device such as P3HT/C₆₀. The former being a donor and the later being an acceptor for the photoinduced electrons. An interpenetrating phase segregated structure of the donor and the acceptor helps fast collection (within few femtoseconds) of the photoinduced carriers. Besides these there are other factors also which affect the efficiency and shelf life of plastic solar cells. We have studied these factors using the solar cell structure ITO/PEDOT:PSS/P3HT:C₆₀/LiF/Al.We have found that the selection of the solvent, morphology of the film and the ratio of the donor P3HT and acceptor C₆₀ (Buck minster fiillerene) are some of the important factors on which the stability and shelf life of the PV cell depend. Selection of a proper solvent on the basis of parameters such as index of refraction, dielectric constant, molecular size and Hildebrand solubility parameter is extremely important in order to achieve high efficiency, stability and long shelf life of the device. It has also been found that increasing the C₆₀ content in the polymer leads to a decrease in degradation of the device but excess amounts of C₆₀ speeds up the degradation process.

Author Index