Narrow Results

CuCo₂O₄ nanoparticles were synthesized via facile hydrothermal route using oxalic as a precipitant, thermal decomposition of CuCo₂O₄ precursor at 400${}^{\circ }$C. The structural studies from X-ray diffraction (XRD), Fourier transform infrared spectrometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose the predominant spinel crystal phase for copper cobaltite. The optical absorption spectra reveal two band gaps of 3.8eV and 4.4eV in the CuCo₂O₄ nanoparticles. The cyclic voltammetry (CV) was used to assess the electrochemical characteristics of the resulting product in an organic electrolyte at −1.5–1.5V under ambient conditions. On 22.4nm CuCo₂O₄ nanoparticles, a greater capacitance of 920F/g at a scan rate of 5mV/s was achieved.

The frequency (100Hz–1MHz) and temperature (30–575°C) dependence of electrical properties of calcium doped (Ca = 0.01, 0.05, 0.1) sodium bismuth titanate (NBT) was investigated by impedance spectroscopy. The data is used to analyze the effect of calcium concentration on the electrical properties of NBT. The frequency explicit plots of Z′′ versus frequency at various temperatures shows peaks in the higher temperature range (>400°C). The relaxation peaks are affected by the doping. The AC conductivity values are computed from the impedance data. DC conductivity has been measured in the temperature range of 30–400°C. The activation energies have been evaluated from the data. From the studies of dielectric constant as a function of temperature, it is observed that diffuse phase transition (DPT) is exhibited in these samples.

The effect of the external velocity field on the transverse impedance of normal liquid ³He has been considered. It is shown that there is an additional frequency dependent term proportional to the current-current correlation function. Vertex corrections to the collisional self-energy have to be treated in order to turn the simple relaxation time into viscous transport time, which is necessary for a quantitative description of the problem.

Safety of the occupant during the crash is very essential design element. Many researches have been investigated in reducing the fatal injury of occupant. They are focusing on the development of a dummy in order to obtain the real human-like motion. However, they have not considered the arm resist motion during the car accident. In this study, we would like to suggest the importance of the reactive force of the arm in a car crash. The influences of reactive force acting on the human upper extremity were investigated using the impedance experimental method with lumped mass model of hand system and a Hybrid III dummy with human-like arm. Impedance parameters (e.g. inertia, spring constant and damping coefficient) of the elbow joint in maximum activation level were measured by free oscillation test using single axis robot. The results showed that without seat belt, the reactive force of human arm reduced the head, chest, and femur injury, and the flexion moment of the neck is higher than that of the conventional dummy.

Ceramic samples of [(Na_1-xK_x)_1/2Bi_1/2 TiO₃] (NKBT) (x = 0.1, 0.15, 0.2, 0.3, 0.45) were prepared by double sintering method. The admittance measurements were carried out in the frequency range of 1 KHz to 10 MHz in the temperature range of 30°C–600°C. The dielectric nature as deduced from admittance data shows a strong temperature and frequency dependence, apart from the relaxor behavior. The admittance data was analyzed by complex plane diagrams i.e., Y′ versus Y′′ at different temperature. The frequency explicit plots of imaginary component of electric modulus (M′′) at various temperatures show peaks shifting to higher frequencies with temperature (> 400°C). The relaxation peaks were effected by the doping. The activation energies are obtained from the data. The electromechanical coefficients K_P, K₃₁ were calculated from the resonant and anti-resonant frequencies obtained from vector admittance plots. The temperature dependence of electromechanical coefficients is studied. The solid solution samples show higher K_P, K₃₁ values as compared to pure sodium bismuth titanate.

Polycrystalline La_3/2Bi_3/2Fe₅O₁₂ (LBIO) compound was prepared by a high-temperature solid-state reaction technique. The complex impedance of LBIO was measured over a wide temperature (i.e., room temperature to 500°C) and frequencies (i.e., 10²–10⁶ Hz) ranges. This study takes advantage of plotting ac data simultaneously in the form of impedance and modulus spectroscopic plots and obey non-Debye type of relaxation process. The Nyquist's plot showed the presence of grain effects in the material at high temperature. The ac conductivity spectrum was found to obey Jonscher's universal power law. The dc conductivity was found to increase with rise in temperature. The activation energy of the compound was found to be 0.24 and 0.51 eV in the low and high-temperature region, respectively, for conduction process.

Potassium-sodium-rubidium niobate single crystals are grown using an original pulling down method, to improve their composition change during a crystal growth, by means of co-doping of small ionic size sodium and large ionic size rubidium into potassium niobate. Even by the co-doping, single crystals can be grown with orthorhombic single-phase at room temperature, as well as pure potassium niobate. Their electric properties, such as the dielectric constant and the impedance, are changed depending on the doping ions.

The polycrystalline sample of KPb₂V₅ O₁₅ was prepared by a mixed-oxide method relatively at low temperature (i.e., 550°C). X-ray diffraction studies of the compound showed the formation of single phase orthorhombic crystal structure at room temperature. SEM micrograph showed the homogeneous distribution of grains throughout the sample. Electric properties were analyzed using the complex impedance spectroscopy. The modulus plot showed the presence of both the grain and grain boundary effect. The bulk impedance evaluated from the Nyquist plots was observed to decrease with the rise in temperature, showing a negative temperature coefficient of resistance. The variation of AC electrical conductivity (σ_AC) was measured in a wide temperature (30–500°C) and frequency (10²–10⁶ Hz) range. The activation energy of the compound calculated from both the impedance and modulus spectrum was found to be the same.

Perovskite structured ferroelectric (Na_1/2 Bi_1/2)_0.945Ba_0.055TiO₃ (BNBT-5.5) material has been synthesized by the conventional sintering technique. X-ray analysis on the material showed a single phase compound with rhombohedral structure with lattice parameters a = 3.89 Åand α = 89.893 Å. Frequency and temperature dependence of dielectric permittivity, impedance, modulus and conductivity have been performed in the frequency and temperature range 45 Hz–5 MHz and 35–595^°C, respectively. The observed low frequency dielectric dispersion (LFDD) in the material could be explained by Jonschers power law and evaluated activation energies at different temperature regions. Impedance spectroscopy study showed the presence of both bulk and grain boundary effects in the materials. The ac conductivity spectrum obeyed the Jonscher's power law. Modulus analysis indicated the possibility of hopping mechanism for electrical process in the system.

We theoretically study the static and dynamic transport properties of Mott–Gurney diodes based on semiconducting single-walled zigzag carbon nanotubes (CNTs). The electric field and velocity distribution of the diode under dc voltage is obtained by solving the steady-state drift-diffusion equations, which involve the negative differential velocity. The current–voltage characteristic of CNT diode exhibits a distinctive positive differential resistance. The high-frequency impedance is calculated with the small-signal analysis method. A major feature of the proposed CNT diode is that the bias- and tube index-dependent impedance show several negative windows in terahertz frequency range despite the positivity of the dc differential resistance. This property makes the CNT-based Mott–Gurney diode a promising candidate for the generation and amplification of terahertz signals within the desired frequency region.

Electrical properties of a series of nanocrystalline aluminium-substituted cobalt ferrite CoAl${}_x$Fe${}_{2-x}$O₄ (CAFO) with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 have been explored. The electrical parameters have been measured by employing impedance and techniques. The impedance has measured as a function of frequency and temperature for all the samples. The impedance increases with the increase in Al concentration in CAFO. Cobalt ferrite is yet to be verified as a ferroelectric material. However, the electrical properties reported here are similar to conventional ferroelectric materials. Multiple (two) electrical phase transitions have been observed, the two transition temperatures are identified as T${}_D$ and T${}_M$ i.e., one is dipole relaxation transition (T${}_D$) and other one is electrical phase transition temperature. Both AC and DC measurements indicate the transition temperatures.

The multiferroic magnetoelectric materials have gained intensive research interest in the recent years due to their prospective applications. In this perspective, the thermally tunable complex impedance, dielectric behavior and room-temperature magnetoelectric coupling of xCo${}_{0.5}$Ni${}_{0.5}$Fe₂O₄–(1 - x)PbZr${}_{0.58}$Ti${}_{0.42}$O₃ (x = 0.2, 0.3 and 0.5) nanocomposites have been investigated. A series of samples have been prepared by chemical pyrophoric reaction process. The structural characterization confirms the coexistence of two different types of phases, there is no phase segregation. The temperature-controlled complex impedance analysis reveals that grain boundaries and grain of the nanocomposites are playing a dominating role. The existence of Maxwell–Wagner interfacial polarization of the nanocomposites causes a high dielectric constant at low frequency. The calculated AC conductivity values with frequency at different temperatures follow the Jonscher’s power-law. A small polaronic hopping contributes largely to the conduction process of the decorated composite. The magnetostriction properties lead to the AC and DC magnetic field-dependent magnetoelectric coupling of the nanocomposites. The magnetoelectric coupling coefficient depends on the concentration of the piezomagnetic phase of the composites.

The temperature dependences of resistance, impedance and capacitance of semitransparent sensor having structure ITO/PTB7-Th:PC${}_{61}$BM/Graphene composite (semisurface type) were investigated. The transparency of the sensor was 58–60%. The dependences of the resistance, impedance and capacitance at different frequencies 100 Hz, 1 kHz, 10 kHz, 100 kHz and 200 kHz and temperature in the range of 23.8–80${}^{\circ }$C for the sensor were studied. It was observed that as the temperature increased from 23.8${}^{\circ }$C to 80${}^{\circ }$C, the resistance and impedance (at 1 kHz) of the samples decreased, on average, by a factor of 3.51 and 3.79, respectively. At same experimental conditions (1 kHz), the capacitances of the samples also decreased by a factor of 9.6. It was also noted that as frequency increased from 100 Hz to 200 kHz, the impedance of the sensor decreased by a factor of 21 and 12, at temperatures 24${}^{\circ }$C and 58${}^{\circ }$C, respectively. Under the same conditions, the capacitance decreased by a factor of 30 and 28, respectively. The temperature resistance coefficients were measured to be −1.31%/${}^{\circ }$C, −1.30%/${}^{\circ }$C, −1.27%/${}^{\circ }$C, −0.84%/${}^{\circ }$C, −0.72%/${}^{\circ }$C and −0.33%/${}^{\circ }$C for R, Z (100 Hz), Z (1 kHz), Z (10 kHz), Z (100 kHz) and Z (200 kHz), respectively. For capacitance measurement, the temperature capacitance coefficients were measured as −1.39%/${}^{\circ }$C, −1.38%/${}^{\circ }$C, −1.37%/${}^{\circ }$C, −1.36%/${}^{\circ }$C and −1.34%/${}^{\circ }$C, respectively. The semitransparent PTB7-Th- and PC${}_{61}$BM-based temperature sensor can be used for measurement of the temperature as a teaching aid in situations where visual control of illumination and light intensity is required.

Magneto tunable left-handed material (LHM) which acts as a composite system has been theoretically demonstrated. The variation of the real and imaginary parts of the effective refractive index of the system is studied. The resonance that occurs in these studies are analyzed. The variation of impedance, reflectivity, absorptivity with frequency of the composite system was observed. The changes in resonance frequency with applied magnetic field are investigated. It is found that the resonance frequency increases with applied magnetic field.

In this work, the dielectric and electrical properties of TlInS₂ crystal have been studied in the temperature range of 300–550 K before and after being implanted with H${}^{+}$ ion. The dielectric parameters such as the real and imaginary parts of permittivity, impedance and dielectric loss have been investigated in this temperature range. The role of free ions in the relaxation process when f$<$ 10 kHz on the basis of the study of dielectric parameters in the frequency range of 25–10⁶ Hz has been determined. It has been observed that the interdependencies of the real and imaginary parts of dielectric permittivity go beyond the standard.

Computer simulated complex immittance spectra of model equivalent circuits involving resistive and capacitive elements are calculated. A comparison of experimentally obtained complex immittance plots of the system Ca_1-xY_xTi_1-xCo_xO₃(x=0.05) with these simulated diagrams greatly facilitates the search for the most appropriate equivalent circuit representing the electrical properties of electronic ceramics.

The ceramic system La_0.7Ca_0.3MnO₃ was prepared by solid state method and impedance measurements were carried out as a function of frequency (100 Hz – 1 MHz) in the temperature range 303–529 K. An equivalent circuit model that represented the data well was arrived at by comparing the experimental plots with computer simulated complex immittance spectra of model circuits. It consisted of three parallel RC circuits connected in series indicating the presence of three processes present in the system. The resistances are found to follow the behavior R = R₀exp(E/kT). The values of activation energy E for these are obtained.

The effect of lanthanum doping on the electromechanical properties of lanthanum-doped sodium bismuth titanate was studied. The ferroelectric system under investigation was Na_1/2(La_xBi_1-x)_1/2TiO₃ ceramics, with x=0, 0.1, 0.15 and 0.2. Admittance measurements were carried out in the frequency range of 100 Hz to 13 MHz and in the temperature range from room temperature to 550°C. Combined impedance and admittance spectroscopy was used to analyze admittance data. The electromechanical parameters were calculated from the resonant and anti-resonant frequencies obtained from vector admittance plots. The electromechanical coefficients for pure sodium bismuth titanate ceramic samples were found to be much larger than the reported values. Also, it was observed that lanthanum-doping decreased the values of electromechanical coupling coefficients.

Polycrystalline Dy-modified Pb_1-xK_2xNb₂O₆ (PKN) ferroelectric ceramic with a general formula Pb_1-xK_2x-3yM_yNb₂O₆ for x=0.20, y=0.10 and M=Dy, have been prepared by the solid-state reaction route. The X-ray diffraction (XRD) studies of the material at room temperature revealed orthorhombic structure with lattice parameters a=17.701 Å, b=17.958 Å and c=3.883 Å. The dielectric anomaly with a sharp peak is observed at 430°C. The impedance plots are used as a tool to analyze the sample behavior as a function of frequency. The grain and grain boundary contributions are estimated. The modulus mechanism indicates the non-Debye type relaxation. The activation energy value near the phase transition temperature has been found to be different in the above T_C from AC conductivity measurements.

The polycrystalline sample of LiPb₂V₅O₁₅ was prepared by a mixed oxide method at low temperature (i.e. 550°C). Preliminary structural analysis confirmed the formation of the compound of an orthorhombic crystal system. The impedance parameters of the material were studied using complex impedance spectroscopy (CIS) in a wide temperature (i.e. 30–450°C) and frequency (i.e. 10²–10⁶ Hz) range. From the complex impedance plots, grain/grain boundary effects and relaxation phenomenon were observed above 30°C. Study of electrical conductivity suggests that the compound exhibits the negative temperature coefficient of resistance (NTCR) behavior like a semiconductor.