Narrow Results

The present contribution provides a strategy to enhance the dielectric constant of polyethylene by chemical modification while not overly compromising its large band gap. Isolated polyethylene chains are considered and the CH2 motifs in the backbone are allowed to be substituted by a number of Group 14 motifs, including SiF₂, SiCl₂, GeF₂, GeCl₂, SnF₂, and SnCl₂, in a systematic, progressive, and exhaustive combinatorial manner. Our results indicate that consecutive SnF₂ or GeF₂ motifs in the polyethylene backbone are most desirable, which can lead to systems with dielectric constant as high as 47.

PbTiO₃ (PT) nanoparticles have been prepared by chemical route using polyvinyl alcohol (PVA) as an efficient surfactant. The effect of PVA to reduce the particle's sizes of PT has been observed. X-ray diffraction (XRD) pattern shows that the PT nanoparticles are tetragonal with distortion ratio, c/a ~1.061. The average particle's size calculated from XRD and transmission/scanning electron microscopy is ~24 nm for PT powder sintered at 700°C. The nanostructured grains were also observed in PT pellet sintered at 1000°C. The dielectric properties of PT pellet have been measured from room temperature to 200°C and in the frequency range of 0.075 to 10 MHz. The values of room temperature dielectric constant and tanδ are 117 and 0.05 respectively, measured at 0.5 MHz. It is found that the dielectric constant of PT nanoparticles can be controlled up to higher frequency region of 5 MHz.

To meet the requirement of next-generation multilayer ceramic capacitors, the synthesis and characterization of Ba_0.985Bi_0.01TiO₃-based high-k dielectric compositions are reported. Solid solutions with a nominal composition of 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_1-xZr_xO₃ (x = 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.1) was synthesized by distillation method. Room-temperature X-ray diffraction patterns showed an increase and then a decrease in the tetragonality of Ba_0.985Bi_0.01TiO₃ after modifying with BaTi_1-xZr_xO₃. The decrement in tetragonality (c/a ratio) was accompanied by lowering of Curie temperature. 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_0.995Zr_0.005O₃ was found to exhibit diffuse phase transition accompanied by an ultrahigh dielectric constant of 77,619, a loss tangent < 1 and a grain size < 1 μm.

Barium thiourea chloride (BTC) single crystals were grown by slow evaporation of aqueous solution. The X-ray and spectral studies confirmed the formation of the title compound. Thermal studies carried out using differential scanning calorimetry (DSC) showed the presence of both the adsorbed and absorbed water in the grown crystal, which can be identified through the peaks around temperatures 80°C and 130°C. The dielectric constant against temperature curve for different frequencies showed concomitant anomaly around the temperature region of 80°C to 120°C similar to a ferroelectric phase transition. We infer that this peak is due to the removal of water and not due to ferroelectric transition and care should be taken while measuring and interpreting dielectric properties of similar hygroscopic crystals containing volatile compounds.

Polymer Nanocomposites (PNC) comprising polyvinylidene fluoride (PVDF)/Multi-walled Carbon Nanotubes (MWCNT) were studied. The structural composition and thermal stability were confirmed from XRD and DSC/TGA data, respectively. The extent of distribution of MWCNT in the PNC increases and the clustering of MWCNT also increases with an increase in the volume fraction of MWCNT ($f_{\mathrm{\text{MWCNT}}})$, as confirmed by FESEM. The PNC shows an insulator-to-metal transition (IMT), with both non-universal percolation threshold $(f_c)$ of $f_{\mathrm{\text{MWCNT}}}=0.006$ and scaling exponents $[s=0.36\pm 0.03,s^{\prime }=1.26\pm 0.1]$, respectively, attributed to adhesiveness/cold pressing and the higher aspect ratio/conductivity of MWCNT. Modulus spectroscopy confirms a non-Debye type universal relaxation behavior $(\beta =0.54)$ only for the percolative sample due to Maxwell–Wagner–Sillars/interfacial polarization, while only dipolar relaxation was probed or the samples below $f_c$. The $f_c$ with static effective dielectric constant $\sim 211$ and low tan $\delta$ may be suitable for charge storage applications.

Ce-doped Bi₂Ti₂O₇ thin films have been successfully prepared on P-type Si substrates by a chemical solution deposition method. The structural properties of the films were studied by X-ray diffraction. The phase of Ce-doped Bi₂Ti₂O₇ was more stable than that of Bi₂Ti₂O₇ without Ce substitution. The films exhibited good insulating properties at room temperature. The dielectric constant of the films annealed at 700°C at 100 kHz was 168 and the dissipation factor was 0.038. All these results showed that Ce-doped Bi₂Ti₂O₇ thin films could be used as storage capacitors in DRAM and MOS.

We report the synthesis of copper oxide (CuO) nanoparticles prepared by wet chemical precipitation method. The structural and dielectric properties are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and complex impedance spectroscopy as a function of frequencies from 40 KHz to 100 KHz in the range of temperatures (308–393K). Maximum value of dielectric constants are found to be in the order of 10⁶ which increases with increase in temperatures. From XRD data it is found that the particle size increases with increase in calcination temperatures. SEM with energy dispersive X-ray fluorescence spectrometer (EDX) results show that only CuO is present in the prepared sample. The selected area electron diffraction (SAED) pattern by TEM shows that uniform size distributions of CuO nanoparticles are present in the sample.

Polyimide-alumina hybrid films were synthesized via in situ polymerization and thermal imidation process from a solution of polyimide precursor and nanosized alumina in N,N-dimethylacetamide, and the microstructure of the hybrid films was characterized by transmission electron microscope (TEM) and infra-red (IR) spectrometry. The dependence of thermal stability, tensile properties, dielectric properties and degradation endurance under corona on the nano-Al₂O₃ content of polyimide-alumina hybrid films was studied. The results show that with the increase of Al₂O₃ content, the thermal stability and the dielectric properties of the hybrids increase, while the tensile properties decrease. Better corona resistance can be achieved if the PI film is filled with α-Al₂O₃ nanometric particle.

In this paper, modified Pb(Zr,Ti)O₃(PZT) antiferroelectric (AFE) ceramics system was investigated by traditional solid state method. It was observed that the effect of different contents of Zr/Sn, Zr/Ti on modified PZT antiferroelectrics. With increasing Zr/Sn content, the E_AFE (electric field of AFE phase to ferroelectric (FE) phase) value was enlarged. The phase switch field was reduced from FE to AFE (E_FA). The hysteresis loops were changed from "slanted" to "square"-types. With increasing Zr/Ti concentrate, the E_AFE value, and also the E_FA was enlarged, while the hysteresis switch ΔE was reduced. The hysteresis loops was from "square" to "slanted"-types. The samples with square hysteresis loops are suitable for energy storage capacitor applications, the composition of ceramics was Pb_0.97La_0.02(Zr_0.90Sn_0.05Ti_0.05)O₃, which have the largest energy storage density ~ 4.426J/cm³ at 227 kV/cm, and ΔE was ~80 kV/cm, energy efficient η was about 0.612.

The comparison of the low temperature sintering and the microwave dielectric properties of Li₂MgSiO₄ (LMS) ceramics prepared by citrate gel (CG) route and solid state (SS) ceramic route are discussed in this paper. The LMS prepared using CG route sintered at 1175°C/2 h has ε_r = 5.3 and tan δ = 1 × 10⁻³ at 9 GHz. The sintering temperature of LMS is lowered to 950°C with the addition of 5 wt% lithium magnesium zinc borosilicate glass and has ε_r = 5.6 and tan δ = 2 × 10^-3 at 9 GHz. The amount of glass required to lower the sintering temperature of ceramics prepared using CG are slightly higher than that of SS ceramic route. The LMS ceramics prepared using SS ceramic route shows excellent microwave dielectric properties with low sintering temperature compared to CG route.

Ca_5-xZn_xNb₄TiO₁₇ ceramics with 0 ≤ x ≤ 0.4 were prepared through a solid-state reaction method. Effects of zinc substitution on sintering behavior and microwave dielectric properties of Ca₅Nb₄TiO₁₇ ceramics were investigated. The sintering temperature was significantly lowered from 1480°C for pure Ca₅Nb₄TiO₁₇ to 1260°C for x = 0.4. The microwave dielectric properties are strongly correlated with the composition. It is worth noting that the temperature coefficient of resonant frequency (τ_f) displays a tendency toward positive value, ranging from −126.4 ppm/°C to −8.6 ppm/°C. A temperature stable microwave ceramic with dielectric constant of 52 and Q × f value of 9937 GHz is achieved at x = 0.4 and is a potential candidate for application as cores in dielectrically loaded antennas.

To investigate the multi-functional ceramics with both high permittivity and large nonlinear coefficient, we have prepared rare-earth Tb-and-Co doped ZnO and TiO₂-rich CaCu₃Ti₄O₁₂ (TCCTO) powders by chemical co-precipitation and sol–gel methods respectively, and then obtained the TCCTO/ZnO composite ceramics, sintered at 1100°C for 3 h in air. Analyzing the composite ceramics of the microstructure and phase composition indicated that the composite ceramics were composed of the main phases of ZnO and CaCu₃Ti₄O₁₂ (CCTO). Our results revealed that the TCCTO/ZnO composite ceramics showed both high dielectric and good nonlinear electrical behaviors. The composite ceramic of TCCTO: ZnO = 0.3 exhibited a high dielectric constant of ~210(1 kHz) with a nonlinear coefficient of ~11. The dielectric behavior of TCCTO/ZnO composite could be explained by the mixture rule. With the high dielectric permittivity and tunable varistor behaviors, the composite ceramics has a potential application for the higher voltage transportation devices.

This paper presents a thorough study of the strain response of different types of electroceramics during dynamical electrical loading. It highlights important aspects to take into account in the experimental methodology and outlines general guidelines for the discussion and interpretation of the results. The contributions of piezoelectric effect, electrostriction and ferroelectric/ferroelastic domain switching to the strain produced during the application of an alternating electric field are discussed by describing the strain-electric field (S-E) loops of different dielectric ceramics in which each of these contributions are predominant. In particular, attention is given to the description of the strain evolution in the characteristic "butterfly loops" typically shown by ferroelectric materials. The strain-polarization loop is indicated as a useful means to reveal the interconnection between strain and polarization state during dynamical electrical loading. Strain rate is suggested as a powerful tool to obtain more detailed information regarding the mechanisms of the electric field-induced strain.

Multilayer dielectric capacitors were fabricated from nanocomposite precursor comprised of BaTiO₃@TiO₂ core–shell nanosized particles and poly(vinylidene fluoride–hexafluoropropylene) (P(VDF–HFP)) polymer matrix (20 vol%). The multilayer capacitors showed very high discharge speed and high discharged energy density of around 2.5 J/cm³ at its breakdown field (~ 166 MV/m). The energy density of the nanocomposite multilayer capacitors was substantially higher than the energy density of commercially used power capacitors. Low cost, flexible structure, high discharge rate and energy density suggest that the nanocomposite multilayer capacitors are promising for energy storage applications in many power devices and systems.

Different weight percentage of ZnBr₂ doped poly(vinyl alcohol) (PVA) free standing composite films were prepared using solution casting method. These films were characterized for analyzing structural, dielectric, electrochemical properties. This paper mainly focused to understand the contribution of physical phenomenon on conductivity in terms of dielectric parameters. FTIR spectrum confirms the interaction between ZnBr₂ and PVA. Pseudo-capacitive behavior observed from cyclic voltammograms. Dielectric properties of the composites follow non-Debye type behavior. The conducting phenomenon occurs due to hopping of ions between coordination sites present in the composite and the segmental relaxation of polymer chain.

At present, it is very important to create new types of mirrors, nonlinear light frequency transformers and optical filters with controlled optical properties. In this connection, it is of great interest to study photonic crystals. Their dielectric permittivity varies periodically in space with a period permitting Bragg diffraction of light. In this paper, we have investigated the optical properties of mesoporous three-dimensional (3D) opal-type and one-dimensional (1D) anodic alumina photonic crystals, filled with different dielectrics, ferroelectrics and piezoelectrics. We have compared the optical properties of initial mesoporous photonic crystals and filled with different substances. The possibility of mesoporous photonic crystals using selective narrow-band light filters in Raman scattering experiments and nonlinear mirrors has been analyzed. The electromagnetic field enhancing in the case of exciting light frequency close to the stop band edges has been established. The optical harmonics and subharmonics generation in mesoporous crystals, filled with ferroelectrics and piezoelectrics was proposed.

Flexoelectricity in dielectrics suggests promising smart structures for sensors, actuators and transducers. In this review, dielectric materials, structures and the associated flexoelectric characterization methods are presented. First of all, we review structures and methods to measure different flexoelectric coefficients, including ${\mu }_{1122},{\mu }_{1111},{\mu }_{1211},{\mu }_{3121},{\mu }_{2312},{\mu }_{1123}$, etc., via direct or converse flexoelectric effect. The flexoelectric materials in the form of bulk, thin films and 2D materials and the reported flexoelectric properties of these dielectrics will then be discussed. Semiconductor materials and the associated flexoelectric studies will also be reviewed. The progress of flexoelectric device study will next be presented, followed by the flexoelectricity research challenges and future trend.

Lead-based electroceramics such as Pb(Zr.Ti)O₃ (PZT) and its derivatives have excellent piezoelectric, pyroelectric and energy storage properties and can be used in a wide range of applications. Potential lead-free replacements for PZT such as potassium sodium niobate (KNN) and sodium bismuth titanate (NBT) have a much more limited range of useful properties and have been optimized primarily for piezoelectric applications. Here, we review the initial results on a new generation of lead-free electroceramics based on BiFeO₃-BaTiO₃ (BF-BT) highlighting the essential crystal chemistry that permits a wide range of functional properties. We demonstrate that with the appropriate dopants and heat treatment, BF-BT can be used to fabricate commercially viable ceramics for applications, ranging from sensors, multilayer actuators, capacitors and high-density energy storage devices. We also assess the potential of BF-BT-based ceramics for electrocaloric and pyroelectric applications.

Incorporation of Te and Gd were done based on the stoicheometric formula PbTi${}_{0.8-x}$ Te${}_{0.2}$Gd_xO₃ (PTTeG). TG characterization of green powder revealed the completion of solid state reaction at temperature 450^∘ C. XRD of modified PTTeG powders milled for 10h was found most suitable as it gives pure single-phase tetragonal structure. Dielectric constant was found as 2543 at curie temperature of 480^∘C in the case of 5wt.% of Gd in PTTeG. Piezoelectric Coefficient was found as 241 $\times$ 10 ${}^{-12}$ C/N at 39Kv/cm of poling field. The results obtained were comparable and even better than so far reported in similar kind of materials.

The novel lead-free ferroelectric relaxor system $x$(Bi(${\text{Zn}}_{2/3}$${\text{Nb}}_{1/3})$${\text{O}}_3)$(1$-x)$BaTiO₃ ($x$BZN(1$-x)$BT) has received interest as a high-capacity relaxor dielectric material. Small quantities (< 10.0 mol.%) of BZN-based dopant had significant impacts on the structure of the BaTiO₃ host. This study evaluates the effect of BZN additions to the BaTiO₃ host up to $x$BZN = 10.0%. Initial additions of BZN were observed to stabilize tetragonal and orthorhombic coexistence at 295 K, alongside increasing dielectric constant. Peak dielectric constant and polarization were observed at $x$ < 4.0%, coinciding with maximum orthorhombic intensity and a local minima in tetragonal intensity. Compositions 0 < $x$ < 4.0% showed increasing polarization and a drop in $T_m$ and classical ferroelectric properties. No significant dielectric dispersion was observed for compositions $x$ < 4.0% over the frequency range 5–640 kHz. Compositions at $x$ > 4.0% showed the onset of dielectric relaxation alongside a drop in polarization coincident with a drop in the tetragonal $c_T$/$a_T$ ratio and the onset of the cubic phase at 295 K. Peak piezoelectric, dielectric and polarization values occurred over the range 3.8% < $x$ < 4.0%, alongside maximum orthorhombic intensity. Subsequent BZN additions showed a rapid onset of dielectric relaxation, alongside an increase in cubic intensity and a continuous drop in $T_m$ with a minima near $x$ = 7.0%. Tetragonal presence at 295 K also vanished to zero at $x$ = 7.0%. Polarization loops ceased showing ferroelectric characteristics at $x$ > 5.0%, showing a transition from lossy relaxor dielectric to low-loss relaxor dielectric at $x$ > 10.0%.