Diffuse Phase Transition Research Articles

The transition from dielectric-temperature stability to diffuse phase transition behavior induced by the sintering temperature for (Ba0.93La0.07)(Ti0.93Tb0.07)O3 ceramics

Nominal (Ba0.93La0.07)(Ti0.93Tb0.07)O3 ceramics (BLTT7) were prepared at different sintering temperatures of Ts = 1100–1400 °C using a mixed-oxide method. The electron paramagnetic resonance (EPR) of Tb4+ in BLTT7 acted as a probe to investigate the effect of Ts on the transition from dielectric-temperature stability to diffuse phase transition behavior. Three tetragonal BLTT7 ceramics sintered at Ts = 1100, 1200 and 1300 °C exhibited increasing dielectric-temperature stability, whereas the pseudocubic BLTT7 sintered at Ts = 1400 °C exhibited a diffuse phase transition behavior with higher permittivity and the temperature stability. A so-called core-shell structure should be responsible for the flattening of the Curie peak at Ts ≤ 1300 °C. The higher Ts (=1400 °C) led to a complete incorporation of La/Tb ions in the BaTiO3 lattice and the collapse of the core-shell structure. The transfer of Tb4+ from the shell at Ts ≤ 1300 °C to the perovskite lattice at Ts = 1400 °C was confirmed by EPR. The solid solution formation of BLTT7 sintered at different Ts is discussed.

Enhanced energy-storage performances of (1-x)PbZrO3-xPbSnO3 antiferroelectric thin films under low electric fields

In this work, (1-x)PbZrO3-xPbSnO3 (PZO-PSO) antiferroelectric thin films were prepared on Pt(111)/Ti/SiO2/Si substrates by a sol-gel method in order to improve energy-storage performances under low electric fields, and the effects of PSO content on microstructures, electrical performances and energy storage behaviors of the thin films were studied in-detail. The results showed that doping PSO in PZO thin films can reduce the stability of antiferroelectric phase, thus ferroelectric polarization of the thin films can reach a lager value at low electric fields. Meanwhile, polyphase components including tetragonal and orthorhombic phase were generated in the PZO-PSO thin films, leading to diffusive phase transition from antiferroelectric to ferroelectric phase under the electric field. Hence, the energy storage behaviors of the PZO-PSO thin films under low electric field were improved significantly. When PSO content was x = 0.48, its energy storage density and efficiency reached the maximum values of 6.11 J/cm3 and 72% at 333 kV/cm, which was 68.26% and 10% higher than pure PZO thin films, respectively. Our results will lay a solid foundation for developing energy-storing antiferroelectric thin films for the application of dielectric capacitors at low electric fields.

Highly Tunable Multifunctional BaTiO3-Based Ferroelectrics via Site Selective Doping Strategy

Electric-field-driven polarization in ferroelectrics delivers extraordinary electro-caloric, electro-optic, and electromechanical properties, etc. However, the controllable multifunctional ferroelectric switching between different electro-related performances still faces great challenges and deserves study. Herein, multifunctional BaTiO3 (BT)-based ferroelectrics are conceived tuning electrocaloric and electrostrictive properties by controlling doping site of dopants, namely site selective doping strategy. The well-concerned Ce is selected for its multivalent trait (Ce3+/Ce4+) and effective adjustment of Curie temperature (TC) in BT. Guided by the distinguished dielectric characteristics via doping Ce3+ in Ba site or Ce4+ in Ti site, BT-based ferroelectrics can direct at different applications. For Ba-site doping, in conjunction with ion-size mismatch effect and defect engineering, manipulating TC to room temperature (RT) and driving second-order-like phase transition are obtained simultaneously. Then, large electrocaloric temperature change (∆Tmax=1.3 K) over a broad temperature span (∆T>1 K, 37~70 ℃) is achieved, which is crucial in developing zero-global-warming-potential refrigeration near RT. For Ti-site doping, unique diffuse phase transition is observed without sacrificing TC, leading to multiphase structures and the formation of nanosize domains, hence facilitating polarization rotation. Therefore, an enhanced electrostrictive strain (S>0.17%) with ultra-low hysteresis (Hhyst<5%) among a wide temperature range is obtained, which challenges toxic lead-contained counterparts in actuators.

Diffusive epidemic process in 3D: a two-species reaction–diffusion phase transition

By the use of Monte Carlo simulation we study the critical behavior of a three-dimensional stochastic lattice model describing a diffusive epidemic propagation process. In this model, healthy (A) and sick (B) individuals diffuse on the lattice with diffusion constants d A and d B , respectively, and undergo reactions B → A and A + B → 2B. We determine the absorbing phase transition between a steady reactive state and a vacuum state. We obtained the order parameter, order parameter fluctuations, correlation length and their critical exponents by the use of steady state and short-time dynamics simulations. We studied three different diffusion regimes: the case of species A diffusing much slower than species B (d A ≪ d B ), the case of species with equal diffusion constants (d A = d B ) and the case of species A diffusing much faster than species B (d A ≫ d B ). We found only second order transition for all three cases. We did not identify any signal of first order transition for the case d A > d B as predicted by field theory in first order approximation.

Na0.5Bi0.5TiO3-based ferroelectric relaxor with high thermal stability and anti-fatigue for charge-discharge properties

Apart from discharge energy density (Wr) and discharging time (t0.9), thermal stability and anti-fatigue for charge-discharge performance are also the important performance indexes for dielectric pulsed capacitor. Na0.5Bi0.5TiO3 based ceramics are usually accompanied by huge electric field-induced strain when appling electric field, resulting in the fatigue phenomenon and thermal accumulation effect in the cycling process. In this work, Na0.5Bi0.5TiO3-xNaNbO3 (NBT-xNN) ferroelectric relaxor ceramic has been prepared by the solid state reaction process. The effect of NaNbO3 content on microstructures, impedance spectroscopy, electric-field-induced strain and charge-discharge performance of NBT-xNN ceramics have been investigated systematically. Results indicate the proper percent of NaNbO3 could favor the formation of polar nanoregions (PNRs), which leads to the diffusion of phase transition and the diminution of electromechanical strain. Therefore, the high thermal stability and anti-fatigue for charge-discharge property has been achieved in NBT-xNN ceramics. An enhanced discharging energy density of 2.44 J cm−3 along with discharge time of 0.31 μs could be obtained in the NBT-xNN with x = 0.3, and a very stable discharge energy density of 2.06 J cm−3 concomitantly with discharge time less than 0.37 μs could be gained in a wide temperature range of 20–150 °C with a fluctuation of ±4% after 104 charge/discharge cycles. This work would contribute to the development of charge-discharge system, especially dielectric capacitor, for green pulsed power devices.

Pseudocapacitance-Dominated Li-Ion Capacitors Showing Remarkable Energy Efficiency by Introducing Amorphous LiFePO4 in the Cathode

Li-ion capacitors (LICs) can be endowed with a satisfying energy density by introducing battery materials in the system, but the polarization of bulk-phase Li insertion, especially from phase transition, sacrifices the crucial energy efficiency at high-power delivery. We herein report the fabrication of a pseudocapacitance-dominated LIC showing advanced energy efficiency and rate capability. The key solution relies on the selective use of nanosized and amorphous LiFePO4 as a cathode, which exhibits pseudocapacitive Li insertion by a solid solution reaction mechanism, thus bypassing the undesired severe phase transition and sluggish ion diffusion in crystalline LiFePO4. After having matched with a highly amorphous carbon anode, the constructed pseudocapacitance-dominated LIC exhibits an excellent energy efficiency of 89% at a maximum energy density of 131 Wh kg–1. Even ultrafast charging at 25 000 W kg–1 (within 11 s), the energy density can still maintain up to 92 Wh kg–1 without the concession of energy efficiency, which is 62% higher than the conventional configuration based on an adsorption-type activated carbon cathode. This demonstrates the broad potential of the designed pseudocapacitance based on an amorphous structure for integrating energy density and energy efficiency in a power-type device like LIC.

Ferroelectric-relaxor crossover induce large electrocaloric effect with ultrawide temperature span in NaNbO3-based lead-free ceramics

In this study, a large electrocaloric effect (ECE) of 0.49 K with an ultrawide temperature span of 80 °C ranging from −15 to 65 °C (0.49 K ± 10%) was reported in the 0.94(0.80NaNbO3–0.20BaTiO3)–0.06Bi0.5Na0.5TiO3 composition. The incorporation of Bi0.5Na0.5TiO3 (BNT) into the NaNbO3–BaTiO3 matrix induced a ferroelectric-to-relaxor (FR) phase transition, accompanied by polar P4 mm evolving to the nonpolar Pm3¯m phase and an increase in the relaxor degree. The inflexions in the peak current density value and Raman spectra indicated a successive downward-shift of FR temperature with the increasing BNT content, which established a continuous modulation of temperature corresponding to the peak ECE in this system. The obtained high ECE performance was believed to originate from an enhanced diffuse phase transition character and coexistence of P4 mm and Pm3¯m phases. This work may provide a guideline to designing high-efficiency solid-state cooling devices that are applied at mutable ambient temperature.

Effect of the degree of a diffuse phase transitions on the behavior of polarization switching processes and elastic properties in multicomponent ceramics based on PZT

It is known that in multicomponent piezoceramics with a certain ratio of the components of the solid solution and modifying impurities, the phase transition from the ferroelectric phase to the paraelectric one occurs in several stages. The temperature interval of such structural and polarization changes, can reach hundreds of degrees. The aim of the present article is to study an effect of a degree of diffuse phase transitions on a character of repolarization and elastic properties in the multicomponents piezoceramics based on PZT.

Effect of sintering temperature on (Ba0.85Ca0.15) (SnxZr0.1-xTi0.9)O3 for piezoelectric energy harvesting applications

The piezoelectric performance of (Ba0.85Ca0.15)(SnxZr0.1-xTi0.9)O3 (BCSZT) ceramics with x = 0, 0.025, 0.05, 0.075, and 0.10 for energy harvesting applications can be optimized by varying the sintering temperature. These BCSZT ceramics were prepared at three different sintering temperatures (1250 °C, 1350 °C and 1450 °C). The relative density for all samples increased as the sintering temperature increased, thereby enhancing the dielectric properties of the BCSZT ceramics. The εmax values of the BCSZT ceramics were improved up to 50% when the sintering temperature was increased from 1250 °C to 1450 °C. The Tc shifted towards a lower temperature (95 °C down to 59 °C) as the Sn content increased. However, the effect of sintering temperature on Tc was barely observed because the variation in grain size between all BCSZT ceramics was very small. Therefore, it was suggested that the sintering temperature had a small impact on Tc because of the diffusibility of the samples. The ΔT value for the BCSZT ceramics was the highest when the samples were sintered at 1250 °C, which meant that the diffuse phase transition was more obvious at lower sintering temperatures. The sample with x = 0.025 showed the most promise as a piezoelectric material for energy harvesting applications.

Ferroelectric soft mode and microwave dielectric relaxation in BaTiO3−PbMg1/3Nb2/3O3 ceramics

${\mathrm{BaTiO}}_{3}$ (BT) is the best-known ferroelectric and $\mathrm{Pb}{\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ (PMN) is the best-known relaxor ferroelectric, but their solid solutions were so far studied only very scarcely. Here the high-density perovskite ceramic solid solutions of $(1\ensuremath{-}x){\mathrm{BaTiO}}_{3}\text{\ensuremath{-}}x\mathrm{Pb}{\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ (BT-100$x$%PMN, $x=0.075$, 0.10, 0.15) were studied by the infrared reflectivity, time-domain terahertz transmission and microwave spectroscopies (1 MHz--20 THz) and compared with the undoped BT and PMN ceramics. The spectra show presence of a split soft phonon at all temperatures, similar to that observed in BT and PMN. Microwave dielectric dispersion was observed both below and above temperature of the diffuse permittivity maximum. In the case of BT-7.5%PMN and BT-10%PMN, the main dispersion takes place above 1 GHz, in case of the BT-15%PMN, the dispersion covers more homogeneously the 1 MHz--1 THz range. The dielectric response up to the THz range of the BT-10%PMN and BT-15%PMN was fitted with three excitations: soft mode, central mode (lower-frequency component of the split soft phonon), and microwave relaxation, but the soft mode does not soften appreciably and only the latter two excitations contribute substantially to the dielectric permittivity maximum. Dielectric response of the BT-7.5%PMN is similar except for the presence of a second dielectric relaxation in the MHz range, also observed in BT. The relaxations show no PMN-like freezing and can be tentatively attributed to the dynamics of polar nanoregions in the paraelectric phase and to the domain/nanodomain wall dynamics and/or acoustic wave emission and piezoelectric resonances within the grains in the ferroelectric phase. In this way, the BT-100$x$%PMN ceramics cannot be considered as relaxor ferroelectrics, but rather as ferroelectrics with the diffuse phase transition. The broadband dielectric spectra of undoped BT ceramics revealed a split optical soft mode and two additional dielectric relaxations which are mainly responsible for the dielectric anomaly at the ferroelectric phase transition. It supports the phase transition in BT to be at the crossover from a displacive to an order-disorder type.

Bi(Mg0.5Hf0.5)O3-modified SrTiO3 lead-free ceramics for high-temperature energy storage capacitors

Lead-free (1 − x)SrTiO3–xBi(Mg0.5Hf0.5)O3 (0.05 ≤ x ≤ 0.4) ceramics were prepared by high-temperature solid-state sintering method. The microstructure, dielectric properties, and energy storage performance were investigated. The diffused phase transition was observed in samples with x ≥ 0.1, showing typical relaxor characteristic. In particular, 0.8ST-0.2BMH composition exhibits stable dielectric permittivity with variation below 15% over temperature range of − 100 °C to 185 °C, superior to that of undoped SrTiO3. The calculated Weibull characteristic breakdown strength is 480 kV/cm for 0.8ST-0.2BMH ceramic, and a large energy density of 4.1 J/cm3 with high energy efficiency of 92% is obtained at electric field of 470 kV/cm. Of particular significance is that the energy efficiency remains above 91% at elevated temperature of 180 °C. In addition, fast discharge time (~ 0.88 µs) with high-power density of 2.8 MW/cm3 is achieved in 0.8ST-0.2BMH ceramic. All the above results indicate that the 0.8ST-0.2BMH relaxor dielectric is a promising lead-free ceramic for high-temperature energy storage applications.

Synthesis, dielectric and ferroelectric properties of BCZTL/BCZTM bilayer ceramics for energy storage applications

(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–3 wt.%Li2CO3/(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–3 wt.%MgO (abbreviation as BCZTL/BCZTM) bilayer ceramics are prepared by the conventional solid-state reaction method. A single-perovskite structure and the diffused phase transition behavior are found in the BCZTL/BCZTM bilayer ceramics by XRD and e − T curves. The bilayer ceramics show high energy storage density (Wrec) 258 mJ/cm3 and good energy storage efficiency (η) 82.9%. Moreover, compared with the BCZTL and BCZTM ceramics, the recoverable energy storage density of BCZTL/BCZTM bilayer ceramics has, respectively, increased by 25.8% and 10.7%. And the bilayer ceramics exhibit a good thermostability with a smaller change rate (13.38%) of Wrec. Meanwhile, the energy storage efficiency obviously increases from 84.0% at 20 °C to 91.6% at 100 °C, which indicates that the BCZTL/BCZTM bilayer ceramics have a potential application in energy storage systems.

Role of charge compensation mechanism and defect dipoles on properties of Mn doped BCT ceramics

Single-phase Mn doped Barium Calcium Titanate (BCT) (Ba0.80Ca0.20Ti1-xMnxO3; x = 0.000, 0.005, 0.010, 0.015 and 0.020) lead free ceramics have been prepared by conventional solid-state reaction method. XRD studies and Rietveld refinement confirmed the existence of tetragonal phase (P4mm) for all prepared ceramic compositions. The average grain size increased up to x = 0.005 and thereafter it decreased with increase in Mn content in BCT compositions. Analysis of temperature-dependent dielectric study revealed phase transformation from tetragonal to cubic phase and defect dipole induced anomaly in paraelectric region of temperature-dependent dielectric constant (εʹ–T) curve. Degree of diffusiveness increased with Mn doping in BCT ceramics as confirmed by evaluating diffused phase transition (DPT) parameters (γ and δc) by Power Law fitting and width of diffused phase transition (Dʹ) obtained from derivative of εʹ–T curve. Ferroelectric (P-E loops) study revealed that ceramic composition with x = 0.015 Mn content showed the highest remnant polarization (Pr) and maximum polarization (Pmax) of 14.10 μC/cm2 and 24.20 μC/cm2 respectively. Enhancement in energy storage properties with applied electric fields have been observed at room temperature. Maximum energy storage density Wrec ̴ 190.89 mJ/cm3 with an efficiency of 48.63% has been obtained for x = 0.015. A large piezoelectric charge coefficient (d33) of 460 pC/N has been obtained for x = 0.020. The room temperature magnetic measurements shows feeble ferromagnetism for Mn doped samples. These studies suggest the application of these ceramics for multilayer ceramic capacitors, energy storage, and high power applications.

Diffuse phase transition and thermal hysteresis in relaxor ferroelectrics from modified Ising model

&lt;sec&gt; Relaxor ferroelectric is a very special type of ferroelectric material, which has important applications in communication, sensor, ultrasound, energy conversion, and aerospace industry. Unlike normal ferroelectric, a relaxor undergoes a diffuse phase transition in the cooling process, and its macroscopic polarization does not occur suddenly, but polar nano region appears while the macro-symmetry does not change significantly. As the transition from the paraelecric to the ferroelectric phase is a gradual process with a broad dielectric peak, relaxor ferroelectric has no definite Curie temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;), and the temperature corresponding to the maximum dielectric constant (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;m&lt;/sub&gt;) and the Burns temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;B&lt;/sub&gt;) are often used as their characteristic temperatures.&lt;/sec&gt;&lt;sec&gt; Here, in order to understand the diffuse phase transition and its internal mechanism, we build a modified Ising model by introducing an energy potential well that affects the spin variable (which is regarded as electric dipole in this research) and simulate the phase transition process using this model, which results in significantly smoothed phase transition with respect to temperature, exhibiting relaxor characteristics with diffuse phase transitions. More precisely, it is found that by applying the energy potential well to the dipoles in the system, the ferroelectric phase transition can be significantly broadened, that is, a diffused phase transition appears, showing strong relaxation characteristics that, as the temperature gradually increases, the average electric dipole moment does not change abruptly while the peak value of its permittivity decreases with the energy potential well. Moreover, at a temperature much higher than the transition temperature of the usual Ising model, the system can still maintain a certain polarization, which is in line with relaxor characteristics. By comparing to a previously proposed statistical model, it is found that the relaxation phenomenon is due to the fact that dipoles in the system are constrained by the given potential well, therefore difficult to flip, making the overall polarizability deviate from that of conventional ferroelectrics. Our results therefore show that the existence of dipole energy potential well is an important factor in the relaxation phenomenon of ferroelectric.&lt;/sec&gt;&lt;sec&gt; This modified Ising model, which accounts for the constrained dipoles statistically, is then used to investigate the thermal hysteresis effect of relaxor ferroelectrics in order to understand its origin. By comparing to experimental results, we are able to clarify the physics of the thermal hysteresis of relaxor ferroelectric, deepening our understanding from the theoretical and simulation perspective.&lt;/sec&gt;

Simulation and optimization of silicon/carbon core-shell structures in lithium-ion batteries based on electrochemical-mechanical coupling model

Silicon is considered as a first candidate for ideal anode material of the next-generation lithium-ion battery due to its high theoretical capacity to meet the demand for higher energy density. On the other hand, high theoretical capacity is accompanied by massive volume expansion, which gives arise to high stress and crack and pulverization of anode particles. Finally, the capacity of the battery fades gradually. While some kinds of factors contribute to the failure of silicon-based electrodes, the most important one is the diffusion-induced stress generated in silicon-based electrode particles. The cyclic processes of lithiation and delithiation are accomplished by the intercalation into and deintercalation from the silicon particles of lithium ions. During the cycle, physical processes and chemical processes, such as diffusion of lithium ions, phase transition, and volume expansion, take place simultaneously, making the cyclic process a strong-coupling problem to be addressed. For example, the intercalation of lithium ions into the electrode results in volume expansion and phase transition of anodes, thereby inducing stress; in turn, stress affects the diffusion process of lithium ions. Aiming to probe this problem, with the finite deformation hypothesis, an electrochemical-mechanical coupling model is used to study the variation and distribution of concentration and stress of core-shell structure during lithiation. And more importantly, great emphasis is put on the optimal design of core-shell structure. The numerical results show that the shell is useful in prohibiting the volume expansion of silicon core, but large compressive radial stress in silicon core may cause the core and shell to be detached, while the tangential tensile stress at the core-shell interface leads the shell to fracture. To improve the electrochemical and mechanical performance and hence lengthen the cycle life of lithium-ion batteries, two kinds of optimal designs are considered: 1) single-layered core-shell structure and 2) double-layered core-shell structure. The numerical results suggest that the softer shell material is suitable for a single-layered core-shell structure and the inner-soft &amp; outer-hard design is optimal for the double-layered core-shell structure. Furthermore, the effects of Young's modulus of the inner and outer carbon layer materials on the chemical and mechanical performance of anode are explored. The simulation shows that the optimal Young's modulus of the inner shell is less than 10 GPa, and that of the outer shell is not higher than 70 GPa. This research is helpful in designing and optimizing the silicon-based anode electrodes of lithium-ion batteries.

Characterization of PTC effect in BaTiO3-ceramics as a special phase transition - fractal approach

The applications of BaTiO3-ceramics are very important and constantly increasing nowadays. In that sense, we analyzed some phenomena related to intergranular effects. We used experimental data based on Murata powders and processing technology. Our original contribution to Heywang-Jonker-Daniels inter-granular capacity model is based on thermodynamic fractal analysis applied on phase transition in ceramic structures. In this case, PTCR effect has a diffuse first-order phase transition character in a modified Landau theory-fractal approach. Its basic properties are considered. This is an original contribution as a bridge between theoretical aspects of BaTiO3-ceramics and experimental results.

Effects of Gd-substitution on structural, and impedance spectroscopic study of Sr2Sm1−xGdxTi2Nb3O15 tungsten bronze ceramics

In the present work, we have studied the effect of Gd-substitution on the structural, dielectric and electrical properties of Sr2Sm1−xGdxTi2Nb3O15 (x = 0 and 0.5) tungsten bronze ceramics prepared by a high-temperature solid-state reaction technique. The formation of the phase of tetragonal tungsten bronze was verified by the Rietveld refinement using X-ray diffraction data. With increasing Gd concentration, the crystal structure of the Sr2Sm1−xGdxTi2Nb3O15 ceramics has slightly deformed from the tetragonal P4bm phase to the paraelectric P4/mbm phase. Scanning electron microscopy (SEM) of ceramics shows high densification and homogeneous distribution of grains of different sizes over the total surface. The crystallite size increases with Gd-substitution from 6.19 nm for Sr2SmTi2Nb3O15 to 10.83 nm for Sr2Sm0.5Gd0.5Ti2Nb3O15. The sample Sr2SmTi2Nb3O15 shows a dielectric anomaly of ferroelectric paraelectric type at 332 °C, and has non-relaxor type of diffuse phase transition. In addition, the dielectric properties deteriorated and even disappeared for the sample Sr2Sm0.5Gd0.5Ti2Nb3O15, because the ceramic presented a P4/mbm phase structure as a result of the decrease in Curie temperature (Tc) below room temperature. The electrical property of Sr2Sm1−xGdxTi2Nb3O15 ceramic has been investigated by non-destructive complex impedance spectroscopy (CIS) as a function of frequency at different temperatures.

Effects of sintering temperature on structure and electrical properties of (Na0.48k0.473Li0.04Sr0.007)(Nb0.883Ta0.05Sb0.06Ti0.007)O3 piezoelectric ceramics

In this study, the effects of sintering temperature on microstructure, dielectric and piezoelectric properties are investigated for the non-stoichiometric (Na0.48K0.473Li0.04Sr0.007)(Nb0.883Ta0.05Sb0.06Ti0.007)O3 (NKLNTSST) piezoelectric ceramics. The results suggest that the piezoelectric properties are enhanced owing to the more normal ferroelectric characteristics, higher density, more uniform grains and presence of polymorphic phase transition regions, which are observed with an increase in the sintering temperature up to 1080?C. The piezoelectric properties are weakened owing to the larger degree of diffuse phase transition and more cationoxygen-vacancy pairs with an increase in the sintering temperature above 1080?C. The best piezoelectric properties including kp = 40%, d33 = 288 pC/N, ?max = 72.12, loss = 2.57%, Ec = 13.45 kV/cm and Pr = 10.23 ?C/cm2 are obtained at the sintering temperature of 1080?C.

Electrical features of ferroelectric (Ba0.83Ca0.17)TiO3 ceramics with diffused phase transition under pressure

Ferroelectric (Ba0.83Ca0.17)TiO3 ceramics was sintered by the solid state reaction method. The material was sintered in three steps that allowed remarkably modifying structure and electrical features important from an application point of view. Major tetragonal phase of the material was detected using X-ray diffraction study. The scanning electron microscope test showed fluctuation in chemical composition. The ferroelectric to paraelectric phase transition was diffused and markedly shifted to lower temperature, TC = 339 K, respectively to barium titanate. Moreover, it showed the pressure sensitivity dTC/dp = −37 K/GPa. These effects were attributed to local disorder both in Ba/Ca and Ti sublattices. The high magnitude dielectric permittivity, ε′~1000–2000, was observed in 200–400 K temperature range. The net polarization, which was estimated from the pyroelectric effect, decreased from ~3 µC/cm2 to zero in ~100–400 K range. The ceramics displayed the piezoelectric coefficient, d33 = 58 pC/N, the spontaneous polarization, PS = 11–14 µC/cm2, the remnant polarization, PR~2 µC/cm2, the coercive field, EC~1.5–3 kV/cm, and the energy density storage efficiency factor, ξ ≈ 33%, at room temperature.

Electric properties of Mn-substituted Na0.5Bi0.5TiO3 ceramics in unpoled and poled states

ABSTRACT The Mn-substituted NBT ceramics were prepared by the conventional ceramic fabrication technique. X-ray diffraction (XRD) studies indicated the formation of perovskite phase with rhombohedral symmetry and with small amount of second phase. It was found that 0.5mol% and 0.1mol% dopant concentration enhances piezoelectric coefficients of d33 and k33, increases the depolarization temperature Td and decreases the dielectric loss. Dielectric study showed the existence of a diffuse phase transition at Tm ≈ 320°C. It was shown that a prior electric field poling process changes the character of ϵ(T) and tanδ(T) functions, as well as shifts of Td and Tm to higher temperature. The effects are mainly caused by the reinforcement of polarization/domain ordering and by the change of content rhombohedral/tetragonal phases by electric field action. The results were discussed in terms of lattice distortion and change of defect concentration.