Temperature Of Permittivity Maximum Research Articles

Relaxation behavior in 0.24Pb(In1/2Nb1/2)O3–0.49Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 ferroelectric single crystal

Dielectric relaxation properties of the ternary relaxor-based ferroelectric 0.24Pb(In1/2Nb1/2)O3–0.49Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 single crystal have been investigated as a function of temperature (300–570K) in the frequency range from 100Hz to 100kHz. It was found that the variation of the permittivity maximum temperature Tm with frequency obeys the Vogel–Fulcher relationship. The high-temperature (T>Tm) side of the dielectric permittivity deviated from the Curie–Weiss law, but can be described by the Lorenz-type relationship. The coercive field obtained from the polarization hysteresis loops gradually decreases with increasing temperature, and the remnant polarization persists above Tm due to the existence of polar nanoregions (PNRs).

Enhanced microstructure and electrical properties of Mn-modified Bi0.5(Na0.65K0.35)0.5TiO3 ferroelectric ceramics

Bi0.5(Na0.65K0.35)0.5TiO3 (BNKT) and Mn-modified Bi0.5(Na0.65K0.35)0.5(MnxTi1−x)O3 (BNKMT-103x), (x=0.0–0.5%) ferroelectric ceramics were synthesized by solid-state reaction method. Optimization of calcination temperature in Mn-doped ceramics was carried out for the removal of secondary phases observed in XRD analysis. BNKMT ceramics sintered at 1090°C showed enhanced dielectric, piezoelectric and ferroelectric properties in comparison to pure BNKT. The average grain size was found to increase from 0.35μm in BNKT to 0.52μm in Bi0.5(Na0.65K0.35)0.5(Mn0.0025Ti0.9975)O3 (BNKMT-2.5) ceramics. The dielectric permittivity maximum temperature (Tm) was increased to a maximum of 345°C with Mn-modification. AC conductivity analysis was performed as a function of temperature and frequency to investigate the conduction behavior and determine activation energies. Significant high value of piezoelectric charge coefficient (d33=176pC/N) was achieved in BNKMT 2.5 ceramics. Improved temperature stability of ferroelectric behavior was observed in the temperature dependent P–E hysteresis loops as a result of Mn-incorporation. The fatigue free nature along with enhanced dielectric and ferroelectric properties make BNKMT-2.5 ceramic a promising candidate for replacing lead based ceramics in device applications.

Large electric field-induced strain and piezoelectric responses of lead-free Bi0.5(Na0.80K0.20)0.5TiO3-Ba(Ti0.90Sn0.10)O3 ceramics near morphotropic phase boundary

Lead-free piezoelectric ceramics with compositions belonging to family of compositions (1−x)Bi0.5(Na0.80K0.20)0.5TiO3-xBa(Ti0.90Sn0.10)O3 or (1−x) BNKT-xBTS (when x = 0.05 − 0.15 mol fraction) near the morphotropic phase boundary (MPB) were fabricated by a conventional mixed oxide method. Sintered samples had relative densities greater than 98% of their theoretical values. X-ray diffraction data revealed that the MPB region consisted of coexisting rhombohedral and tetragonal phases in the BNKT-BTS system was identified over the entire compositional range. A large electric field-induced strain (Smax) of 0.36% and a normalized strain coefficient (d*33) of 649 pm/V were observed in the BNKT-0.05BTS sample. The sample close to the MPB composition (BNKT-0.11BTS) exhibited the maximum dielectric constant (er = 1770), temperature of maximum permittivity (Tm = 333C°) and low-field piezoelectric coefficient (d33 = 227 pC/N), along with reasonable ferroelectric properties (Pr = 20.6 mC/cm2, Rsq = 0.88) and strain properties (d*33 = 445 pm/V and Smax = 0.24%).

Preparation and piezoelectric properties of self-polarized (Na,Bi)TiO3–BaTiO3 thin films on Si substrate

The c-axis oriented polycrystalline thin film of (Na,Bi)TiO3–BaTiO3 (NBT–BT) around the morphotropic phase boundary (MPB) was prepared on an LaNiO3-buffered Si substrate by rf magnetron sputtering. The NBT–BT film showed a large crystal lattice distortion in the out-of-plane direction, and a voltage shift of the hysteresis loop along the negative field axis as large as −200 kV/cm, which indicates that the film is internally biased and strongly self-polarized towards the top electrode. Owing to the large internal bias field, the NBT–BT film exhibited a linear piezoelectric response with the piezoelectric coefficient, , reaching −4.8 C/cm2 in the unipolar excitation and a low dielectric permittivity of 230. The temperature-dependent dielectric properties revealed that the permittivity maximum temperature, Tm, of the NBT–BT film was significantly enhanced to ∼550 °C from the ∼300 °C of bulk NBT–BT, accompanied by the disappearance of the depolarization temperature, Td, which is confirmed by the structural data where the crystal lattice remained unchanged up to ∼400 °C. These stable temperature properties would lead to an expansion of the temperature range of use of NBT–BT film.

Dielectric and AC-conductivity studies of Dy2O3 doped (K0.5Na0.5)NbO3 ceramics

(K0.5Na0.5)NbO3 + x wt.% Dy2O3 (x = 0–1.5) ferroelectric ceramics were prepared by conventional solid state reaction method. XRD patterns revealed that orthorhombic symmetry has transformed into psuedocubic symmetry with increasing the substitution of Dy3+ in the Na+ site. Temperature and frequency dependences of relative dielectric permittivity maximum conforms the transformation from normal ferroelectric to relaxor ferroelectric behaviour. Frequency dependence of the relative dielectric permittivity maximum temperature observed for the samples with x ≥ 1.0 and satisfied the Vogel–Fulcher law. The diffuseness exponent γ (1.27–1.95) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals that the degree of relaxor behavior increases with increasing the amount of Dy2O3. The temperature dependence of AC-conductivity σAC (T) analysis in the range 310 K < T < 470 K reveals the existence of variable range hopping of charge carriers with average hopping length RH and hopping energy EH are in the range 8.5–27 Å and 48–153 meV, respectively. Voltage dependent dielectric constant measurements confirm the ferroelectric nature of KNN+ x wt% Dy2O3 ceramics.

Synthesis and characterization of lead-free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic

Polycrystalline sample of lead-free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic has been synthesized by solid state reaction method. Single-phase perovskite structure with rhombohedral symmetry was confirmed by x-ray diffraction. Temperature dependent dielectric permittivity studies demonstrated frequency independent behavior, indicating that the studied sample was not a typical relaxor ferroelectric. A polymorphic phase transition between rhombohedral and tetragonal phase was noticed near room temperature followed by a tetragonal to cubic transition with 97 °C as the temperature of maximum permittivity. The macroscopic values of d33 and d31 were ∼350 pC/N and −141 pm/V, whereas the electromechanical coupling factors kp and kt were 44.5% and 41.6%, respectively. Bulk P-E hysteresis loop was obtained with saturation polarization 11 μC/cm2 and coercive field ∼4 kV/cm. Distinct polarization contrast with a complex mosaic-like domain structure was observed in the out-of-plane mode of piezoresponse force microscopy. The domain width and the correlation length were estimated to be nearly 2 μm and 827 nm, respectively. Local hysteresis loop with apparent coercive voltage, Vc = 15.8 V, was observed.

Effect of La2O3 Addition on Electrical Properties of PZN-PZT Based Ceramics

In this study, compositions in the 0.2Pb(Zn1/3Nb2/3)O3-0.8Pb(Zr1/2Ti1/2)O3 based systems will be developed based on the material engineering approach (processing vs. electrical properties). This work involves the fabrication of high purity PZN-PZT based in ceramic forms, and a study of La2O3 addition on phase formation, microstructures and electrical properties was investigated which are especially important from the viewpoint of the development of practical piezoelectric materials. The effect of La2O3 addition was characterized on microstructure and electrical properties of PZN-PZT. Amounts of 0.05–1 wt% La2O3 were doped on 0.2PZN-0.8PZT. All compositions of powders were uniaxially pressed in pellets and sintered at the temperature 1250°C with dwell time 2 h. Phase and microstructure development, dielectric and ferroelectric properties of ceramics were characterized by XRD, SEM, LCR meter and Modified Sawyer–Tower Circuit respectively. In addition, the values of permittivity maximum and the temperature of permittivity maximum were substantially decreased by La-doping and these results show increased Pr, Ps and strain level but decreased Ec.

Static and dynamic polar nanoregions in relaxor ferroelectric Ba(Ti1−xSnx)O3system at high temperature

Relaxor ferroelectrics are materials exhibiting dielectric dispersions in their maximum permittivity temperature without macroscopic phase transition into a ferroelectric state. Their exceptional properties are exploited in a variety of dielectric and piezoelectric applications. As it is generally believed that polar nanoregions play a crucial role in relaxor behavior, there are great interests in exploring how the atomic structures affect the relaxor properties. Here, using the dark field imaging and atomic-resolution electron microscopy, we investigate the nano and atomic structure of a lead-free ferroelectric-relaxor Ba(Ti${}_{1\ensuremath{-}x}$Sn${}_{x}$)O${}_{3}$ system at high temperature. The local atom displacements and their spatial correlations are measured, and the atomic structure of static polar nanoregions in the relaxors is reported. For the materials exhibiting normal ferroelectricity, no such static polar structures can be seen. Based on our experimental observations, we suggest the static polar nanoregions are responsible for the relaxor behavior in this lead-free system.

Dielectric and Piezoelectric Properties of Lead-free (1-x)BaTiO3-xBiScO3 Ceramics

The structural, dielectric and piezoelectric characteristics of lead-free (1−x)BaTiO3-xBiScO3 (0 ≤ x ≤ 0.45) solid solution ceramics synthesized by using a solid state reaction have been investigated for use in high-temperature applications. Their polycrystalline structure change from a tetragonal ferroelectric phase to a pseudocubic phase at 0.04 < x < 0.08, and secondary impurity peaks appear at x = 0.45. The temperature-dependent dielectric constants indicate a phase transition that becomes more diffuse as x increases and a crossover from a diffuse phase transition (DPT) to a relaxor behavior that takes place at 0.04 < x < 0.08. The dielectric permittivity maximum temperature, Tm, increases with increasing BiScO3 content above x = 0.08. The values of the piezoelectric coefficient (d33) and the electromechanical coupling factor (kp) decrease rapidly with increasing x. Ceramics with x = 0.01 show a coercive field of about 6.6 kV/cm and a remanent polarization near 8.5 μC/cm, which are maximum values for (1− x)BaTiO3-xBiScO3 systems.

Dielectric characterization of (1-x)pmn-xpt (x = 0.07 and 0.10) ceramics synthesized by an ethylene glycol-based soft chemical route

Materials based on relaxor ferroelectrics have become one of the most important families of functional materials being explored for such applications as sensors/actuators, micro-electromechanical systems (MEMS), non-volatile random access memories, and high-energy-density capacitors. Fabrication of high-quality relaxor-based ceramics remains, however, a challenging task. In this work, a new soft chemical synthetic method for the preparation of the complex perovskite-based relaxor ferroelectric solid solutions, (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) was developed using ethylene glycol as the solvent. Ceramics with compositions of x = 0.07 and 0.10 were prepared and it was found that a 10% stoichiometric excess of Pb(2+) was required to compensate for lead oxide volatility at the high temperatures used for sintering. The ceramics produced by this method show excellent dielectric properties at room temperature, such as a high dielectric constant (~20 000) and low loss over a large temperatures range (tan δ < 0.01 between 20 and 200°C). The temperature dependence of the dielectric constant exhibits typical relaxor ferroelectric behavior, fitting a quadratic law which describes the high-temperature slope of ε'(T) peak. The frequency dispersion of the temperature of maximum permittivity satisfies the Vogel-Fulcher law.

Temperature evolution of the local structure in relaxor ferroelectric Ba(Ti 0.7Zr 0.3)O 3 studied using neutron total scattering analysis

We performed neutron total scattering measurements on relaxor ferroelectric Ba(Ti 0.7Zr 0.3)O 3 from T = 350 to 50 K. Using reverse Monte Carlo modeling on the total scattering data in k-space as well as in real space, we show that the off-centering of Ti ion is the source of local polarization at all temperatures. In addition, we estimated that Ti displacement is toward the 〈 111 〉 direction with a magnitude of about ∼0.11 Å. We also present an evolution of Ti–O bond length distribution across the maximum permittivity temperature, which suggests a freezing of local polarization with decreasing temperature.

Effect of WO 3 doping on dielectric and ferroelectric properties of 0.94(Bi 0.5Na 0.5)TiO 3–0.06BaTiO 3 ceramics

WO 3(0–6 mol%)-doped 0.94Bi 0.5Na 0.5TiO 3–0.06BaTiO 3 lead-free ceramics were synthesized by conventional solid-state reaction. The effect of WO 3 addition on the structure and electrical properties were investigated. The result revealed that a small amount of WO 3 (≤1 mol%) can diffuse into the lattice and does not significantly affect the phase structure, however, more addition will result in distortion and enlargement of the unit cells. The maximum permittivity temperature ( T m) is suppressed dramatically as the dopant increasing, while the depolarization temperature ( T d) fall to the minimum with 1 mol% WO 3 additive. The remanent polarization ( P r) was enhanced and coercive field ( E c) was reduced by doping with WO 3. The strain shows the largest value for 1 mol% doped sample, which is due to a field-induced antiferroelectric–ferroelectric phase transition.

Giant Electrocaloric Effect in High-Energy Electron Irradiated P(VDF-TrFE) Copolymers

ABSTRACTA direct calorimetry method was developed and used to measure the electrocaloric effect (ECE). A temperature change ΔT of over 20 °C and an entropy change ΔS of over 95 J/(kgK) were procured at 33 °C and 160 MV/m in the high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 68/32 mol% copolymers, which were larger than those of terpolymer blends (ΔT = 9 °C, ΔS=46 J/(kgK) at 180 MV/m and room temperature) and our earlier report on P(VDF-TrFE) 55/45 mol% normal ferroelectric copolymer (12 °C and 55 J/(kgK) at 80 °C). We observed that the β value ((8.7±0.6)×107 JmC-2K-1) in the equation of ΔS=1/2βΔD2 derived from ΔS - ΔD2 relation for irradiated copolymers was larger than that of the terpolymer blends ((5.4±0.5)×107 JmC-2K-1). It was also found that the irradiated copolymer showed a sharp depolarization peak at Td &lt; Tm (maximum permittivity temperature), which is frequency independent, in the dielectric constant - temperature characteristics, a larger depolarization value at Td in the thermally stimulated depolarization current (TSDC) - temperature relationship, and a larger volume strain/longitudinal strain ratio over terpolymer blends. The giant ECE in irradiated copolymer is regarded as due to the greater randomness present in the relaxor state. In irradiated copolymers, the long all-trans chains are broken by the high-energy electrons, which make the small sized all-trans sequences more easily reorient along the electric field, more remarkably affecting the permittivity, TSDC, and volume strain.

Growth and characterization of piezo-/ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3–Bi(Zn1/2Ti1/2)O3 ternary single crystals

In order to develop new piezo-/ferroelectric materials, single crystals of the Pb(Mg1/3Nb2/3)O3−PbTiO3−Bi(Zn1/2Ti1/2)O3 [PMN−PT−BZT] ternary complex perovskite system has been grown by a high temperature solution method using the mixture of PbO and H3BO3 as flux (in a molar ratio of 4:2) with an optimum flux:charge molar ratio of 6:1. It is found that the addition of BZT into the relaxor ferroelectric PMN−PT system reduces the number of spontaneous nucleations, resulting in large single crystals (5mm×5mm×14mm) of good quality. The grown crystals exhibit a pseudo-cubic morphology and show evidence of two-dimensional growth mechanism. Examination by polarized light microscopy (PLM) reveals the formation of striation, which can be reduced by changing the growth conditions. The domain structure and phase transition of the PMN−PT−BZT crystals are investigated by PLM. The temperature and frequency dependences of the dielectric permittivity of the grown crystals show typical relaxor ferroelectric behavior, with the frequency dependence of the temperature of maximum permittivity (Tmax) following the Vogel–Fulcher law. The ferroelectric property is displayed in the crystals with a remnant polarization, Pr=21μC/cm2 and a coercive field, EC=3.5kV/cm. The piezoelectric coefficient, d33, is found to be 825pC/N, a value much higher than that of the ternary ceramics.

Microstructure and electrical properties of Aurivillius phase (CaBi2Nb2O9)1−x(BaBi2Nb2O9)x solid solution

The microstructures and electrical properties of Aurivillius phase ferroelectric solid solutions of (CaBi2Nb2O9)1−x(BaBi2Nb2O9)x (0≤x≤1) have been studied. X-ray diffraction analyses revealed a bismuth layered structure for all compositions. Scanning electron microscope images showed randomly oriented and platelike grain morphology. The Curie point Tc or the maximum permittivity temperature Tm decreased with increasing x. The (CaBi2Nb2O9)1−x(BaBi2Nb2O9)x ceramics exhibited a ferroelectric–paraelectric phase transition at small x values (x≤0.5), whereas a relaxor behavior was observed at high x values (x≥0.8). The d33 value of CaBi2Nb2O9 ceramics was enhanced by Ba2+ doping on the A-sites (x≤0.3). A combination of high d33 values and high Tc points (&amp;gt;700 °C) suggests that compositions with x≤0.3 could be good candidates for high-temperature piezoelectric applications. The composition with x=0.8 is a relaxor ferroelectric with Tm around 320 °C at 1 MHz.

Strong variation of electrostrictive coupling near an intermediate temperature of relaxor ferroelectrics

A sudden increase in the electrostrictive coefficient ${Q}_{13}$ when temperature decreases is seen in three different types of ferroelectric relaxors (PLZT 9/65/35, PLZT 22/20/80, and PMN-PT) starting from $\ensuremath{\sim}50\text{ }\text{K}$ above the dielectric permittivity maximum temperature, ${T}_{m}$. The temperature dependence is attributed to the softening of the quasilocal mode occurring near dopants or charge-transfer sites. The steep increase when the temperature decreases could be related to the transition of polar nanoregions from dynamic to quasistatic regime, which introduces an intermediate temperature scale ${T}^{\ensuremath{\ast}}$ [W. Dmowski, S. B. Vakhrushev, I.-K. Jeong, M. P. Hehlen, F. Trouw, and T. Egami, Phys. Rev. Lett. 100, 137602 (2008); B. Dkhil, P. Gemeiner, A. Al-Barakaty, L. Bellaiche, E. Dul'kin, E. Mojaev, and M. Roth, Phys. Rev. B 80, 064103 (2009)], besides Burns temperature ${T}_{B}$ and freezing temperature ${T}_{f}$. Possible consequences for nonequilibrium phenomena, including high-temperature memory found in relaxors, are conjectured.

Study on Bi 2O 3 doping methods and dielectric property of (1 − x)BaTiO 3– x(Bi 0.5Na 0.5)TiO 3 ceramics

Extensive studies on Bi 2O 3 doping methods and contents of (1 − x)BaTiO 3– x(Bi 0.5Na 0.5)TiO 3 ((1 − x)BT– xBNT, x = 0.01, 0.03, 0.05, 0.10, 0.15, 0.25 mol) ceramics have been investigated. The samples were fabricated by the conventional ceramic process, while Bi 2O 3, Na 2CO 3, and TiO 2 were doped in the molar ratio of 1:1:4 and 1.005:1:4 (Bi-excess), respectively, to create (Bi 0.5Na 0.5)TiO 3. The temperature dependence dielectric constant and loss revealed that (1 − x)BT– xBNT ceramics had a typical relaxor behavior and diffuse phase transition characteristics and the degree of ferroelectric relaxation behavior was enhanced with the increase of BNT-dopant concentration. In addition, all the tan δ– T curves showed a low and broad platform under 100 °C. The room temperature permittivity decreased sharply at x ≤ 0.05 mol and then they varied slowly with x increasing. The temperature of permittivity maximum ( T m) could be improved when x ≤ 0.15 mol and this tendency was more apparent when doped with excess Bi 2O 3.

Dielectric, ferroelectric and pyroelectric properties of Pb[(Ni1/3Sb2/3)xTiyZrz]O3 ceramics

In the present study, various Pb[(Ni1/3Sb2/3)xTiyZrz]O3 where x+y+z=1, x=0.08 and y=0.44–0.49, ceramics in the morphotropic phase boundary (MPB) range were studied by dielectric and pyroelectric methods. The results of the investigations revealed an MPB composition range of y≅0.46. The study of the dielectric properties of these compounds as a function of temperature suggests that with increase in y the permittivity maximum increases and transition temperature shifts towards higher temperature. Well-saturated polarization versus electric field (P–E) hysteresis loops were obtained and values of Pr were calculated. The samples revealed good pyroelectric properties for y=0.44 and y=0.45 at room temperature with large figures of merit Fv=0.019 m2/C and FD=1.34×10–5Pa1/2.

Ferroelectric relaxor behaviour in Pb(Fe0.5Ta0.5)O3

The relaxor ferroelectric lead iron tantalate, Pb(Fe0.5Ta0.5)O3 (PFT) is synthesized by Coulombite precursor method. The X-ray diffraction pattern of the sample at room temperature shows a cubic phase. The field dependence of dielectric response is measured in a frequency range 0.1 kHz — 1 MHz and in a temperature range from 173–373 K. The temperature dependence of permittivity (ɛ′) shows broad maxima at various frequencies. The frequency dependence of the permittivity maximum temperature (T m ) has been modelled using Vogel-Fulcher relation.

Some Properties of the Relaxor-Like Behavior in Sodium Niobate-Based Binary Solid Solutions

Some crystallochemical regularities of the appearance of relaxor-like dielectric behavior in binary (1-x)NaNbO 3 -(x)ABO 3 solid solutions have been revealed. The most significant frequency shift of permittivity maximum temperature T m is observed for solid solutions, where the aliovalent ion substitutions take place in both cationic sublattices of NaNbO 3 , or for solid solutions, where the difference in the valency of the dopant and host ions exceeds unity. A linear correlation between the frequency shift of T m and the parameter δ of the permittivity maximum diffusion was revealed.