Temperature Dependence Of Dielectric Constant Research Articles

Switchable Dielectric Materials Based on a Diprotonated Organic Cation Containing Two Different Anions: (C5H16N2)BF4X (X = Cl, Br, NO3)

Three molecular-based phase transition compounds, namely, (C5H16N2)BF4Cl (1, C5H16N2 = diprotonated 2,2-dimethyl-1,3-propanediamine), (C5H16N2)BF4Br (2), and (C5H16N2)BF4NO3 (3), were synthesized and characterized. Differential scanning calorimetry and the step-like anomaly of the real part (ε′) of the temperature-dependent dielectric constant revealed that the compounds underwent reversible first-order phase transition with high phase transition temperature under the stimulation of temperature. Variable-temperature X-ray diffraction analysis revealed that the microcosmic driving force of phase transition was the order–disordered change of the organic cation and spherical anion. Notably, the diprotonated organic cations were charge-balanced by two different anions of the combination BF4– and Cl–, Br– and NO3–. Our research paves a new avenue to construct molecular-based phase transition materials with temperature stimulus response.

New insight into effects of oxygen vacancies on crystal structure and electrical properties of barium titanate dielectric ceramic

The oxygen vacancies in perovskite-type dielectric ceramic influence the crystal structure and electrical properties of the ceramics significantly. In the work, the oxygen vacancies are investigated for typical barium titanate (BT) ceramic through a control of sintering atmosphere. A lattice deformation with preferred orientation of (111), (002) and (200) planes are observed due to the oxygen vacancies. The electrical properties are systematically studied through temperature-dependent dielectric constants, leakage currents, complex impedance spectra and breakdown strengthens (Eb). The results suggest that the oxygen vacancies account for low resistance, low Eb and large leakage current. Such variations are elaborated from the views of the energy band structure based on the DFT and the finite element simulation. Besides, the mechanical properties are calculated and the increased elastic constant (C) along z-axis and modulus of BT-Vo gives rise to the sharply decreased of piezoelectric constant (d33).

Composition-spread epitaxial ferroelectric thin films for temperature-insensitive functional devices

Ba<sub><i>x</i></sub>Sr<sub>1–<i>x</i></sub>TiO<sub>3</sub> (BST) ferroelectric thin films are widely used in microwave tunable devices due to their high dielectric constants, strong electric field tunabilities and low microwave losses. However, because of the temperature dependence of dielectric constant in ferroelectric material, the high-tunability for conventional single component ferroelectric thin film can only be achieved in the vicinity of Curie Temperature (<i>T</i><sub>C</sub>) which leads the ferroelectric thin films to be difficult to operate in a wide temperature range. To obtain ferroelectric thin films for temperature stable functional devices, single composition Ba<sub>0.2</sub>Sr<sub>0.8</sub>TiO<sub>3</sub> thin films, Ba<sub>0.5</sub>Sr<sub>0.5</sub>TiO<sub>3</sub> thin films, and Ba<sub>0.2</sub>Sr<sub>0.8</sub>TiO<sub>3</sub>/Ba<sub>0.5</sub>Sr<sub>0.5</sub>TiO<sub>3</sub> heterostructure thin films are deposited by pulsed laser deposition (PLD). By comparing their dielectric properties in a wide temperature range, it is found that the temperature sensitivity of BST film can be effectively reduced by introducing a composition gradient along the epitaxial direction. However, the heterostructure engineering may bring extra troubles caused by interfaces, which may limit the quality factor <i>Q</i>. In this paper, we extend our combinatorial film deposition technique to ferroelectric materials, and we successfully fabricate in-plane composition-spread Ba<sub>1–<i>x</i></sub>Sr<sub><i>x</i></sub>TiO<sub>3</sub> thin films, which are expected to broaden the phase transition temperature ranges of BST films while avoiding the problem of interface control.

Phase-Transition Behaviors of Crystalline Hypophosphorous Acid and a Feasible Incommensurate Wave-like Array of the Proton Displacements from Each Center of Hydrogen Bonds along the 1-Dimensional Chain

Crystalline hypophosphorous acid, composed of strongly hydrogen-bonded chains, was investigated by adiabatic calorimetry in a temperature range between 20 and 306 K and by dielectrometry as a supplemental means. The heat-capacity curve showed subsequent phase transitions: a second-order one at 210.4 K followed by a first-order one at 159 K and the other two ones at 149 and 139.4 K with decreasing temperature. The total entropy of the transitions was assessed to be 0.35 J K–1 mol–1 by using the baseline heat capacities that were determined by means of a real-coded genetic algorithm. The small value was interpreted as the transitions were associated with displacements of the protons forming hydrogen bonds: namely, while they are located at the center between two oxygen atoms above 210.4 K, the protons are displaced close to one of the oxygen atoms with the bond length enlarged below it. Temperature dependence of dielectric constants displayed no sign, around 210 K, indicating the existence of (anti-)ferroelectricity. It was thus expected that the manner of off-center proton displacements along each hydrogen-bonded chain reveals a wave-like and incommensurate appearance below 210.4 K, referred to as the normal crystal lattice above it, and following locking to a wave-like but superlattice commensurate one at 159 K.

Optical and temperature dependent electrical properties of poly (vinyl chloride)/copper alumina nanocomposites for optoelectronic devices

Abstract The practical applications of poly (vinyl chloride) have been constrained due to its poor thermal stability, low dielectric constant and inability to shield against ultraviolet (UV) radiation. In this study, we tried to improve the optical properties, thermal stability, temperature-dependent electrical conductivity and dielectric constant using copper alumina (Cu–Al2O3) nanoparticles reinforced poly (vinyl chloride) (PVC). Optical absorption measured with an ultraviolet-visible (UV-visible) spectrometer emphasises the blueshift in absorption edges and decreasing bandgap energies of PVC/Cu–Al2O3 nanocomposites compared to PVC. The presence of Cu–Al2O3 in PVC and its interaction with the polymer were confirmed by FTIR spectroscopy. Thermogravimetric analysis (TGA) demonstrates that nanocomposites have higher thermal stability than PVC, and that thermal stability increases with filler loading. Scanning electron microscopy (SEM) indicates the homogeneous dispersion of nanosized Cu–Al2O3 in the polymer matrix. The activation energy determined by the Arrhenius equation revealed that AC conductivity increases with the addition of nanoparticles up to a specific loading. The dielectric constant increases as a function of temperature and decreases with frequency. The magnitude of AC conductivity and dielectric constant were highest for 7 wt% loaded nanocomposites. The dielectric constant predicted by the Bruggeman and Maxwell-Garnet models were in good agreement with the experimental permittivity. The semiconducting nature of nanocomposites was investigated by impedance analysis. The semi-circular nature of Cole-Cole plots manifests the combination of parallel capacitance with low bulk resistance. The enhanced optical, thermal, electrical and dielectric properties of PVC/Cu–Al2O3 nanocomposites can be utilized in fabricating optoelectronic devices with excellent charge-storing ability.

Influence of concentration and temperature dependent dielectric constants on the thermodynamics of electrolytes

The symmetric Poisson–Boltzmann theory, the modified Poisson–Boltzmann theory, and the mean spherical approximation are utilized to calculate the osmotic coefficient, and the individual and mean activity coefficients of model KCl, LiCl, NaCl, and NaClO4 electrolytes all dissociated in water where the dielectric constant depends on concentration. The theories are also employed to compute the same thermodynamic quantities for HCl and NaCl solutions where the dielectric constant is now temperature dependent. In each situation the theoretical predictions are compared with the corresponding exact benchmark Monte Carlo simulation results. The mean spherical approximation and the modified Poisson–Boltzmann theory reproduce the simulation data for osmotic coefficient quantitatively and that for the mean activity almost quantitatively. The individual activities are accurately represented by the modified Poisson–Boltzmann theory but only qualitatively by the symmetric Poisson–Boltzmann and the mean spherical approximation. In general, the symmetric Poisson–Boltzmann theory shows good agreement with the simulations at low concentrations but deviates at higher concentrations.

Effect of Ni content, temperature on the electrical and colorimetric properties of nano NixZn(1-x)O blue pigments

Nanosized Ni doped ZnO (NixZn1-xO, with 20 ≤ × ≤ 70) were synthesized by simple coprecipitation method at different calcinations temperature (400, 600, 800 and 1000 o C). All synthesized oxides well characterized by XRD, scanning electron microscopy (SEM). The electrical properties and the colorimetric parameters (CIEL L* a* b*) were measured. The results obviously show that Ni2+ ions incorporated into the ZnO structure without difficulty. For the highest concentration of Ni2+ for x = 0.40 and 0.70 of Ni2+ doping, the XRD revealed an extra diffraction peak characteristic to NiO, indicating an upper limit of Ni concentration. The crystallite size was discovered to be between 13 and 109 nm. With the addition of Ni to the ZnO, the temperature dependency of electrical conductivity of samples increases. The temperature dependence of dielectric constant of samples is found to decrease with incorporation of Ni in the solution. The samples show very good blue color with load 20% of Ni.

Influence of Mn Ions' Insertion in Pseudo-Tetragonal Phased CaBi4Ti4O15-Based Ceramics for Highly Efficient Energy Storage Devices and High-Temperature Piezoelectric Applications.

In the present era of advanced technology, the surge for suitable multifunctional materials capable of operating above 300 °C has increased for the utilization of high-temperature piezoelectric devices. For this purpose, a pseudo-tetragonal phased CaBi4Ti3.98 (Nb0.5Fe0.5)0.02O15:xwt%MnO2 (CBTNF:xMn), with x = 0-0.20, ceramic system has been engineered for the investigation of structural, ferroelectric, dielectric and high-temperature-dependent piezoelectric properties. XRD analysis confirms that low-content Mn-ion insertion at the lattice sites of CBTNF does not distort the pseudo-tetragonal phase lattice of CBTNF:xMn ceramics, but enhances the functional behavior of the ceramic system, specifically at x = 0.15 wt%Mn. Compared to pure CBT and CBTNF ceramics, CBTNF:0.15Mn has demonstrated a highly dense relative density (~96%), a saturated polarization (PS) of 15.89 µC/cm2, a storage energy density (WST) of ~1.82 J/cm3, an energy-conversion efficiency (ƞ) of ~51% and an upgraded piezoelectric behavior (d33) of 27.1 pC/N at room temperature. Sharp temperature-dependent dielectric constant (εr) peaks display the solid ferroelectric behavior of the CBTNF:0.15Mn sample with a Curie temperature (TC) of 766 °C. The thermally stable piezoelectric performance of the CBTNF:0.15Mn ceramic was observed at 600 °C, with just a 0.8% d33 loss (25 pC/N). The achieved results signify that multi-valence Mn ions have effectively intercalated at the lattice sites of the pseudo-tetragonal phased CBTNF counterpart and enhanced the multifunctional properties of the ceramic system, proving it to be a durable contender for utilization in energy-storage applications and stable high-temperature piezoelectric applications.

Refractory Plasmonic Hafnium Nitride and Zirconium Nitride Thin Films as Alternatives to Silver for Solar Mirror Applications.

Harnessing solar energy by employing concentrated solar power (CSP) systems requires materials with high electrical conductivity and optical reflectivity. Silver, with its excellent optical reflectance, is traditionally used as a reflective layer in solar mirrors for CSP technologies. However, silver is soft and expensive, quickly tarnishes, and requires a protective layer of glass for practical applications. Moreover, supply-side constraints and high-temperature instability of silver have led to the search for alternative materials that exhibit high solar and infrared reflectance. Transition metal nitrides, such as titanium nitride, have emerged as alternative plasmonic materials to gold starting from a spectral range of ∼500 nm. However, to achieve high solar reflection (∼320-2500 nm), materials with epsilon-near-zero starting from the near-ultraviolet (UV) spectral region are required. Here, we show the development of refractory epitaxial hafnium nitride (HfN) and zirconium nitride (ZrN) thin films as excellent mirrors with a solar reflectivity of ∼90.3% and an infrared reflectivity of ∼95%. Low-loss and high-quality epsilon-near-zero resonance at near-UV (∼340-380 nm) spectral regions are achieved in HfN and ZrN by carefully controlling the stoichiometry, leading to a sharp increase in the reflection edge that is on par with silver. Temperature-dependent reflectivity and dielectric constants are further measured to demonstrate their high-temperature suitability. The development of refractory epitaxial HfN and ZrN thin films with high solar and infrared reflectance makes them excellent alternative plasmonic materials to silver and would pave their applications in CSP, daytime radiative cooling, and others.

Anomalous dielectric response in the triple perovskite ruthenate Ba3BiRu2O9

We have investigated the magnetic, dielectric and thermal properties of the S = 1 magnetic dimer Ba3BiRu2O9, which is known to exhibit a spin-gap opening in conjunction with a first-order magneto-elastic phase transition at ∼175 K. Above the spin-gap temperature, the temperature dependence dielectric constant shows a peak like feature with pronounced frequency dependence. The critical slowing down behavior of this frequency dispersion suggests that a ferroelectric relaxor like electrical glassy state exists above the spin-gap opening temperature regime. The extermination of frequency dispersion—right at the magneto-elastic phase transition, is suggestive of a strong coupling between the lattice and charge-spin degrees of freedom in this triple perovskite system.

Magnetodielectric effect and significant magnetoelectric coupling of Co3NiNb2O9 single crystal

A4B2O9 (A = Co, Fe, Mn, Ni, B = Nb, Ta) compounds with a corundum-type structure can host multiferroic phenomena and present magnetoelectric coupling to achieve manipulations of their ground states by external fields. High quality Ni-doped Co4Nb2O9 single crystals of Co3NiNb2O9 have been synthesized for the first time using optical floating zone technique. Co3NiNb2O9 exhibits an antiferromagnetic order at 32 K with an easy magnetization axis in the ab plane. Field-dependent magnetizations at 20 K along [100] and [120] directions have a slope change at 6 and 9 kOe, respectively, indicating a spin-flop transition or spin rotation in the ab plane. Temperature dependence of dielectric constants along [100] and [120] directions show a magnetic-field-induced peak near the antiferromagnetic transition, proving a sizable magnetodielectric effect. Pyroelectric currents along [100] and [120] directions also have a divergent behavior near the transition under magnetic fields, manifesting a magnetoelectric coupling effect. The electric polarization along [120] direction reaches 128 μC/m2 under a magnetic field of 40 kOe, larger than that in most phases of the A4B2O9 system.

Dielectric, impedance and conductivity properties of pristine and (Gd, Ru)-dual doped NiO nanoparticles

This study investigates the synthesis of Ni 1–2x Gd x Ru x O nanoparticles, with different concentrations of Gd and Ru dual dopants, in an attempt to improve their dielectric and electrical properties. These samples are synthesized via the co-precipitation method, and characterized by various structural, methods, including the X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM), and Raman spectroscopy. The XRD patterns demonstrated the formation of single NiO phase, revealing the good incorporation of (Gd, Ru) in NiO lattice. The crystallite size decreased from 21 to 10 nm with increasing the dual dopants’ concentration. The TEM images demonstrated pseudo-spherical morphology of the Ni 1–2x Gd x Ru x O nanoparticles and the Raman spectra detected the fundamental vibrational modes of NiO. The frequency and temperature-dependent dielectric constants were augmented by the incorporation of the dual dopants, due to the induced nickel vacancies and larger surface-to-volume ratio. The Nyquist plots demonstrated depressed semicircles with smaller radii as the temperature and the dual dopants’ concentration increased. This was related to the enhancement of ac conductivity that followed different trends at room and high temperatures. The ac conductivity was tuned by varying the dual dopants concentration due to the ionic compensation mechanism, and the changes in the charge carriers’ concentrations and mobility. The correlation between the different dielectric and electric parameters suggested the dominance of the long-range conduction of the charge carriers. • Ni 1−x Gd x Ru x O nanoparticles, with x = 0–0.02, were prepared by co-precipitation method. • Gd and Ru dual dopants improved the dielectric properties of NiO nanoparticles. • Parallel RC circuits fitted the Nyquist plots with less R for higher dual dopants. • AC conductivity increased with dual dopants that were ionically compensated in NiO. • Gd and Ru dual dopants increased the interest in NiO for electronic applications.

Vibrational probes of anharmonic interactions in the molecular ferroelectric 2-methylbenzimidazole

We report experimental and computational characterization of the anharmonic interactions between the constituents of the molecular ferroelectric material 2-methylbenzimi-dazole (MBI). Using experimental Raman spectroscopy measurements across a wide range of temperatures we assess the anharmonic properties of this material’s vibrations we expect to play a major role in proton tautomerism (PT) mechanism that explain ferroelectric switching in MBI. Through an application of the standard theory of anharmonic contributions to the interatomic potential energy of MBI we develop and apply a method to decipher how cubic and quartic anharmonic coupling to low frequency lattice vibrations affect the frequency of an intramolecular ring vibration of the molecular constituents of this material capable of modulating carbon-nitrogen double bonds that alternate in the PT mechanism. In addition, we use the theory of vibrational solitons to show the appearance of satellites peaks red-shifted from the N-H stretching vibration of MBI stem from self-trapped vibron states. We assess the number of these trapped states and the modes along which trapping occurs to show MBI possesses distinct phases in which excitations of the N-H stretching vibration couple to different low frequency lattice vibrational modes. We propose increased N-H stretching vibrational trapping at low temperature helps explain reductions in the temperature-dependent dielectric constant of MBI measured previously. These results highlight the important role vibrational spectroscopy can play in understanding how intermolecular interactions impact the structural dynamics of materials central to sustainable information storage and nonlinear optical technologies

Hysteretic temperature dependence of resistance controlled by gate voltage in LaAlO3/SrTiO3 heterointerface electron system

For two-dimensional electron gas device applications, it is important to understand how electrical-transport properties are controlled by gate voltage. Here, we report gate voltage-controllable hysteresis in the resistance–temperature characteristics of two-dimensional electron gas at LaAlO3/SrTiO3 heterointerface. Electron channels made of the LaAlO3/SrTiO3 heterointerface showed hysteretic resistance–temperature behavior: the measured resistance was significantly higher during upward temperature sweeps in thermal cycling tests. Such hysteretic behavior was observed only after application of positive back-gate voltages below 50 K in the thermal cycle, and the magnitude of hysteresis increased with the applied back-gate voltage. To explain this gate-controlled resistance hysteresis, we propose a mechanism based on electron trapping at impurity sites, in conjunction with the strong temperature-dependent dielectric constant of the SrTiO3 substrate. Our model explains well the observed gate-controlled hysteresis of the resistance–temperature characteristics, and the mechanism should be also applicable to other SrTiO3-based oxide systems, paving the way to applications of oxide heterostructures to electronic devices.

Synthesis, structural evolution, and dielectric properties of a new perovskite solid solution (Pb0.5Sr0.5)(Zr0.5Ti0.5)O3–PbTiO3

AbstractTo explore lead‐reduced dielectric materials in the SrTiO3–PbTiO3–PbZrO3 ternary system, a novel solid solution between relaxor ferroelectric (Pb0.5Sr0.5)(Zr0.5Ti0.5)O3 and ferroelectric PbTiO3, namely (1 − x)(Pb0.5Sr0.5) (Zr0.5Ti0.5)O3–xPbTiO3 (lead–strontium–zirconate–titanate [PSZT]–PT), has been synthesized in the perovskite structure by high‐temperature solid‐state reaction method in the form of ceramics. The crystal structure and phase symmetry of the materials synthesized were analyzed and resolved based on X‐ray powder diffraction (XRD) data through both the Pawley and Rietveld refinements. The results of the structural refinements indicate that at low PT‐concentration end of the solid solution system, for example, x = 0.05, the PSZT–PT solid solution exhibits a cubic structural symmetry (with the space group Pm‐3m). As the PT concentration (x) increases, the structure of (1 − x)PSZT–xPT gradually transforms from the cubic to a tetragonal (P4mm) phase. In the composition range of x = 0.10–0.25, a mixture of the cubic and tetragonal phases was identified. As the concentration of PT increases, the proportion of the tetragonal phase increases at the expense of the cubic phase. For a composition of x > 0.25, a pure tetragonal phase is observed. The dielectric properties of the materials were studied by measuring the permittivity as a function of temperature at various frequencies. For the composition of x = 0.05, the temperature dependence of dielectric constant shows typical relaxor behavior. For x = 0.35, the dielectric peaks indicate a normal ferroelectric phase transition. Overall, a structural transformation from a central‐symmetric, nonpolar cubic phase to a non‐centrosymmetric, polar tetragonal phase is induced by the substitution of PT for PSZT in the pseudo‐binary solid solution of (1 − x)PSZT–xPT, which also reveals an interesting relaxor to ferroelectric crossover phenomenon.

Dielectric anomalies and structure evolution of annealed (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 ceramics

The (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 [(1-x)PST-xPIN] (x = 0.2, 0.4, 0.6, and 0.8) solid-solution ceramics were synthesized by conventional solid-state reaction method. The phase structure, microstructure, and dielectric properties were analysed. In order to obtain various ordering degrees, annealing treatment at 700 °C for 10 h, 20 h, 40 h, and 120 h was conducted on (1-x)PST-xPIN ceramics. The degree of ordering increased significantly with the extension of annealing time in 0.8PST-0.2PIN composition. However, for other compositions, no any superlattice peak was observed at all times of annealing process, which was related to the presence of more pyrochlore phase. In addition to the low-temperature relaxation peaks associated with the disordered arrangement of B-site ions, two new dielectric anomalies were found in the temperature dependence of dielectric constant of annealed (1-x)PST-xPIN solid solution. For annealed 0.8PST-0.2PIN composition, the middle-temperature and high-temperature dielectric anomalies were attributed to the ordered PST region and the incommensurate structure induced by the competition between ordered PST and disordered PST, respectively. The high-temperature dielectric anomalies in 0.6PST-0.4PIN and 0.4PST-0.6PIN compositions originated from the contribution of the ordered PIN region in solid solution. Furthermore, the relatively weak superlattice diffraction spots of (111) were found in selected-area electron diffraction patterns of annealed 0.8PST-0.2PIN ceramic, indicating that the existence of alternately ordering arrangement of B-site ions. Combined with the analysis of element mapping, it was concluded that the annealed (1-x)PST-xPIN solid solution was composed of the ordered PST region, the ordered PIN region, and the disordered region constituted by PST and/or PIN.

Enhanced dielectric and optical properties in Al-substituted KBiFe2O5

We report a significant effect of Aluminum (Al3+) substitution on the structural, optical and dielectric properties in brownmillerite KBiFe2O5 (KBFO) multiferroic. Polycrystalline samples of KBiFe2-xAlxO5 (x = 0, 0.2) are synthesized by citrate combustion method. From the Rietveld refinement of X-ray diffraction analysis, both the samples are found to crystalize in a monoclinic structure possessing P2/c space group. The calculated crystallite size from the Scherer’s formula is found to decrease with Al doping. The surface morphology reveals that, multiple grains of different sizes are present in all the samples and the average grain size is reduced with substitution. The optical band gap decreases from 1.739 eV to 1.715 eV with x = 0.2 of Aluminum. Furthermore, the temperature dependent Dielectric constant (ε) and dielectric loss (tan δ) of KBiFe2-xAlxO5 are investigated in a temperature range (300–773 K) at 100 Hz and 1 KHz frequency shows a substantial variation followed by a transition at around 550 K for all the samples. A comparative analysis for both the systems reveals that, for x = 0.2 of Al, an order of increase of dielectric constant appears as compared to the parent system. Additionally, the dielectric loss is also found to decrease with doping as compared to pure KBFO.

Temperature-dependent dielectric property of a nematic liquid crystal doped with two differently–shaped tungsten oxide (W18O49) nanostructures

In this work, we investigated the temperature-dependent dielectric constants (ε|| and ε⊥), and dielectric anisotropy (Δε = ε|| - ε⊥) of two differently–shaped tungsten oxide (W18O49) nanoparticles (NPs) doped into a nematic liquid crystal (NLC). We used nanowire and urchin forms of W18O49 at different concentrations and shapes to obtain NP-NLC composite. The results demonstrate that by adding NPs up to a certain concentration, ε||, ε⊥, and Δε are decreased, and then it increased. Results demonstrate a great agreement between the experimental result with the dielectric constant model for the NP-NLC composite. Our results showed that the shape and the concentration of W18O49 NPs can be significantly impacted the temperature-dependent dielectric property in the NP-NLC systems.

Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi4Ti4O15 High-Temperature Piezoelectric Ceramics.

In this work, SrBi4Ti4O15 (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd2O3, CeO2, MnO2 and Cr2O3) were fabricated by a conventional solid-state reaction route. The effects of oxide additives on the phase structures and electrical properties of the SBT ceramics were investigated. Firstly, X-ray diffraction analysis revealed that all these oxides-modified SBT ceramics prepared presented a single SrBi4Ti4O15 phase with orthorhombic symmetry and space group of Bb21m, the change in cell parameters indicated that these oxide additives had diffused into the crystalline lattice of SBT and formed solid solutions with it. The SBT ceramics with the addition of MnO2 achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd2O3 could increase the TC of SBT. At a low frequency of 100 Hz, those dielectric loss peaks appearing around 500 °C were attributed to the space-charge relaxation as an extrinsic dielectric response. The synergetic doping of CeO2 and Cr2O3 could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr2O3 can significantly enhance both d33 and kp of SBT, and produce a higher phase-angle maximum at resonance. Such an enhanced piezoelectricity was attributed to the further increased orthorhombic distortion after Ti4+ at B-site was substituted by Cr3+. Among these compositions, Sr0.92Gd0.053Bi4Ti4O15 + 0.2 wt% Cr2O3 (SGBT-Cr) presented the best electrical properties including TC = 555 °C, tan δ = 0.4%, kp = 6.35% and d33 = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d33 was decreased by only 3.6% after being annealed at 500 °C for 4 h. Such advantages provided this material with potential applications in the high-stability piezoelectric sensors operated below 500 °C.

Effect of BaSnO3 on structural and electrical properties of lead free Na0.5Bi0.5TiO3 ceramic solid solution

A series of novel lead-free (1-x)(Na0.5Bi0.5)TiO3–xBaSnO3, (x = 0.00, 0.05, 0.10) ceramics were fabricated by solid-state air sintering route and their dielectric and microstructural properties were studied. Various experimental methods to characterize the fabricated ceramics such as PXRD, Raman spectra, SEM-EDS, UV-visible and dielectric studies. All the ceramics were crystallized by rhombohedral symmetry using PXRD and Rietveld profile refinement technique. The experimental atomic charge density distribution studies were performed and the bonding characteristics were analyzed. With increase of BSN content, the average grain size decreased and was characterized by scanning electron microscopy (SEM) technique. Energy dispersive x-ray (EDS) spectra indicate the presence elements and the diffusion of BSN into the rhombohedral phase of NBT matrix. The optical bandgap was determined by UV-Visible spectra and the values are found to be 3.05, 3.10 and 3.12 eV. The temperature dependence of dielectric constant (ε) provides evidence for dielectric anomalous behaviour in the higher doping of BSN concentration.