等静压和温度诱导的PbLa(Zr,Sn,Ti)O3反铁电陶瓷相变和介电性能研究

研究了等静压和温度诱导掺镧La的Pb(Zr,Sn,Ti)O₃(PLZST)陶瓷材料的铁电反铁电相变、介电压力谱和介电温度谱,研究了温度对压致相变和介电压力谱的影响,结果发现温度使铁电反铁电相变压力降低,介电压力谱具有明显的扩散相变和频率弥散的特点;研究了等静压对介电温度谱的影响,结果表明等静压使铁电反铁电相变温度降低,反铁电顺电相变温度升高.这些现象有利于丰富和拓宽人们对温度和压力诱导的多组元弛豫型铁电体和弛豫型反铁电体扩散相变和弛豫行为的认识和理解. 关键词： 等静压和压致相变 铁电反铁电相变 介电压力谱 介电温度谱     

等静压诱导的PbLa(Zr,Sn,Ti)O3陶瓷铁电-反铁电相变性能研究

 研究了等静压诱导掺镧La的Pb(Zr,Sn ,Ti)O₃（PLZST）陶瓷材料的铁电-反铁电相变和介电压谱,结果发现介电压谱具有明显的扩散相变和频率弥散的特点,这一现象有利于拓宽人们对压力诱导的多组元弛豫型铁电体的扩散相变行为的认识和理解。     

Na0.25K0.25Bi0.5TiO3无铅压电陶瓷的介电特性研究

用固相反应法制备了Na_0.25K_0.25Bi_0.5TiO₃ (NKBT50)陶瓷，研究了该陶瓷在室温至400℃温度范围内的介电性能.发现该陶瓷的介电温谱与烧结气氛、极化状态有关.在空气中烧结的未极化样品在70℃附近存在介电和损耗峰，而极化后及在氧气氛中烧结的样品并不存在该介电、损耗峰.分析认为70℃的介电和损耗峰与氧空位形成的缺陷偶极子的极化弛豫有关.热激电流显示，陶瓷的去极化温度为225℃，与此相对应的介电、损耗峰也 关键词： 介电性能 氧空位 极化弛豫 钛酸铋钠钾     

铁电磁体Pb(Fe1/2Nb1/2)O3相变特征

借助与示差扫描量热法、磁化率测量、电子自旋共振、铁电与介电性质测量及电子衍射系统地研究了Pb(Fe_1/2Nb_1/2)O₃(PFN)的电、磁性质和相变特征．结果表明发生在380K附近的顺电－铁电转变和发生在145K附近的顺磁 反铁磁转变分别为一级相变和二级相变或弱一级相变．在室温下,PFN的剩余极化与矫顽场分别为11.5μC/cm²和3.04kV/cm.介电测量表明PFN的顺电-铁电相变为弥散型相变．其弥散指数为1.62.电子衍射表明Fe³⁺与Nb⁵⁺离子在B位置上是无序分布的,正是这种与无序分布相关联的成分涨落导致铁电相变的弥散性. 关键词：     

La诱导(Pb(1-3x/2)Lax)(Zr0.5Sn0.3Ti0.2)O3反铁电介电弛豫研究

采用标准电子陶瓷工艺制备了(Pb_(1-3x/2)La_x)(Zr_0.5Sn_0.3Ti_0.2)O₃(PLZST,0.00≤x≤0.18)反铁电陶瓷,利用X射线衍射、不同频率下弱场介电温谱、强场下的极化强度-电场(P-E)测试研究了材料相结构和电学性能.实验结果发现,随La含量x增大,室温下材料由铁电三方相(关键词： 反铁电陶瓷 介电频率色散 相变弥散 介电弛豫     

铁电单晶0.62Pb(Mg1/3Nb2/3)O3-0.38PbTiO3折射率的研究

用最小偏向角法在20℃下精确测量了0.62Pb(Mg_1/3Nb_2/3)O_{3< /sub>-0.38PbTiO3( 0.62PMN-0.38PT)单晶的折射率，给出了该温度下折射率色散的Sellmeier方程.研究了能带 结构与折射率的关系，计算了样品的Sellmeier光学系数：对no，E0=5.50eV,λ0=0.2 26μm，Ｓ０=1.004×10¹⁴m^-2，Ed=28.1 0eV；对ne，Ｅ0=5.57eV,λ 0=0.223μm，S0=1.017×10¹⁴m^-2，Ed=28.10eV.A BO3型钙钛矿材料中，BO6八面体基元决定了晶体的能带结构，对折 射率产生重要影响. 关键词： PMNT单晶 折射率 Sellmeier光学系数}     

异质界面对Ca(Mg1/3Nb2/3)O3/CaTiO3叠层薄膜结构和介电性能的影响

采用异质叠层方式制备出一定厚度的Ca(Mg_1/3Nb_2/3)O₃/CaTiO₃(CMN/CT)叠层薄膜,研究了异质界面对薄膜结构、微观形貌及介电性能的影响及其规律.根据实验测试结果,提出CMN/CT叠层薄膜的模拟等效电路,建立介电常数和介电损耗的理论计算公式.结果表明:CMN/CT异质叠层薄膜具有完全正交钙钛矿结构,结构致密,厚度均匀,薄膜中存在独立的CMN和CT相.异质界面处存在过渡层,随着薄膜中异质界面个数增加,介电常数增大,介电损耗减小.减小界面过渡层的厚度,有利于提高CMN/CT叠层薄膜的介电性能.     

0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃(PMN-0.3PT)单晶1-3型压电复合材料的性能与单晶体积分数的关系,得出性能最优时压电相的体积分数为64%, 在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k_t高达90.1%,压电系数d₃₃大于1000pC/N,机械品质因数Q_m为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zr_xTi_1-x)O₃(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景. 关键词： PMN-PT单晶 压电复合材料 压电相 聚合物相     

High pyroelectric power generation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

We report the pyroelectric power generation of a relaxor ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) single crystal. For a temperature variation rate of 0.5 K/s, the PMN–PT generated a closed-circuit current of 10 nA and an open-circuit voltage of 1.1 V at room temperature. The pyroelectric current and voltage of the PMN–PT single crystal were proportional to the temperature variation rate and were sharply enhanced near the structural phase-transition temperature. Additionally, the PMN–PT pyroelectric generator produced stable power for excessive thermal cycling and was highly sensitive to random thermal fluctuations. Our results indicate the potential importance of PMN–PT for high-power pyroelectric generator applications.     

Effects of strontium on the characteristics of Pb(Zr1/2Ti1/2)O3--Pb(Zn1/3Nb2/3)O3 ceramics

The dielectric and piezoelectric properties of pyrochlore-free lead zirconate titanate-lead zinc niobate ceramics were investigated systematically as a function of Sr doping. The powders of Pb_{(1? x )}Sr _x [0.7(Zr_{1 / 2}Ti_{1 / 2})–0.3(Zn_{1 / 3}Nb_{2 / 3})]O₃, where x?=?0–0.06 were prepared using the columbite-(wolframite) precursor method. The ceramic materials were characterized using X-ray diffraction, dielectric spectra, hysteresis and electromechanical measurements. The phase-pure perovskite phase of Sr-doped PZN--PZT ceramics was obtained over a wide compositional range. The results showed that the optimized electrical properties were also achieved at composition x?=?0.0, which were K _P?=?0.69, d ₃₃?=?670?pC?N^?1, P _r?=?31.9?µC?cm^?2 and ε_rmax?=?18600. Maximum dielectric constant values of the systems decreased rapidly with increasing Sr concentration. Moreover, with increasing Sr concentration dielectric constant versus temperature curves become gradually broader. The diffuseness parameter increased significantly with Sr doping. Furthermore, Sr doping has been shown to produce a linear reduction in the transition temperature (T _m)?=?294.1–12.7x°C with concentration (x). Sr shifts the transition temperature of this system at a rate of 12.7°C?mol^?1%.     

Perovskite Pb(Sc1/2Nb1/2)O3 nanopowders synthesized by surfactant-modulated precipitation

A novel surfactant-modulated precipitation method is proposed to produce pure perovskite Pb(Sc_1/2Nb_1/2)O₃ (PSN) nanopowders at a low temperature of 700 °C. The samples were characterized by XRD, SEM, TEM, and HRTEM, respectively. The results indicate that the powders exhibit a granular shape of 80 nm in diameter. It is believed that the nanosize of as-prepared PSN powders is dependent on the well-dispersed performance, which arouse from the combined effects of both precipitant TMAH and surfactant CTAB. The mechanism of the formation of the pure perovskite PSN nanopowders is discussed in detail. Our method is expected to create a new, low-cost route to produce the promising nanopowders of multi-component perovskite systems.     

Dielectric response of disordered Pb(Sc1/2Ta1/2)O3 single crystal under hydrostatic pressure

The effect of hydrostatic pressure on the dielectric response of Pb(Sc_1/2Ta_1/2)O₃ single crystal with the degree of order S = 0.16 has been studied. At elevated pressures the dielectric anomaly characteristic of ferroelectric relaxors is shifted to lower temperatures, its amplitude decreases and the relaxor peak becomes more diffused. In the pressure range studied up to 0.75 GPa, the temperature dependencies of the characteristic relaxation time obey the Vogel–Fulcher law. It has been found that the Vogel–Fulcher temperature decreases with increasing pressure while the activation energy of the dipolar entities increases. This increase can be ascribed to the pressure-induced changes in the atom–atom and dipolar interactions, resulting in the increased energy barriers for dipolar fluctuations.     

Effect of Hydrostatic Pressure on the Dielectric Response of Pb(Mg1/3Nb2/3)O3 Relaxor

The effect of hydrostatic pressure on the dielectric response of Pb(Mg_1/3Nb_2/3)O₃ relaxor single crystal was studied. An increase in the dispersion of the dielectric anomaly, characteristic of the relaxors, was observed: pressure-induced downward shift of the temperature T _m of permittivity maximum at 1 kHz amounts to dT _m /dp = ? 3.8 K/100 MPa, whereas that measured at 1 MHz equals ? 3.3 K/100 MPa. Analysis of the dielectric response of the highly polarizable Pb(Mg_1/3Nb_2/3)O₃ shows that hydrostatic pressure results in a decrease of the correlation radius r _c of polar nanodomains, as well as their activation energy.     

A luminescence study of B-type Eu2O3 under pressure

Abstract

Luminescence spectra from Eu³ + ion in B-type (monoclinic) ₂O₃ powder have been recorded at room temperature as a function of pressure using a diamond anvil cell. Changes in the spectral pattern of the Eu³ + ion emission at about 4 GPa indicated that a phase transition to the A-type (hexagonal) structure had taken place. Upon release of the applied pressure, the B-type structure was regained with hysteresis. The spectral shifts with pressure have been used to study the effect of pressure on the spin-orbit interaction of the 4f electrons in the Ed + ion. The relationship between the relative changes in the spin-orbit coupling constant, ζ_4f, and the volume accompanying the phase transition is also discussed.     

弛豫型铁电单晶0.67Pb(Mg_(1/3)Nb_(2/3))O_3-0.33PbTiO_3的拉曼散射研究

本文采用拉曼散射技术在温度从374到-196℃的范围内,研究了弛豫型铁电单晶0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMNT)。观察了在不同温度下拉曼光谱的变化,经分析这些变化反映了该晶体经历了两个相变:第一个相变温度发生在120℃,从顺电立方相到铁电四方相的相变,780 cm-1处模式在VH偏振下的改变标志了这一相变;第二个相变温度发生在34℃,是从铁电四方相到铁电三方相的相变,软模的出现代表了这一相变。     

The transverse laser induced thermoelectric voltages in step flow growth （1-x）Pb(Mg1/3Nb2/3)O3-xPbTiO3 thin films

This paper reports that the transverse laser induced thermoelectric voltages (LITV) are observed for the first time in the step flow growth (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT,x = 0.20, 0.33, 0.50) thin films deposited on vicinal-cut strontium titanate single crystal substrates. Because lead magnesium niobate-lead titanate is a solid solution of lead magnesium niobate (PMN) and lead titanate (PT), there are two types of signals. One is wide with a time response of a microsecond, and the other superimposed with the wide signal is narrow with a time response of a nanosecond. The transverse LITV signals depend on the ratio of PMN to PT drastically. Under the irradiation of 28-ns pulsed KrF excimer laser with the 248-nm wavelength,the largest induced voltage is observed in the 0.50Pb(Mg1/Nb2/3)O3-0.50PbTiO3 films. Moreover, the effects of film thickness, substrates, and tilt angles of substrates are also investigated.     

Successive phase transitions in the highly ordered complex perovskite PbLu1/2Nb1/2O3

The structural phase transitions and the electrical behaviour of the complex perovskite PbLu_1/2Nb_1/2O₃ have been investigated using X-ray powder diffraction, dielectric constant measurements, differential scanning calorimetry and measurement of the polarisation as a function of applied electric field. The high-temperature paraelectric phase is highly ordered. A first-order paraelectric-antiferroelectric phase transition occurs at 270°C and an antiferroelectric-ferroelectric phase transition, characterised by dispersion in the curves of dielectric constant as a function of temperature, occurs at ≈ 30°C. The antiferroelectric phase is isostructural with the orthorhombic form of PbYb1/₂Nb1/₂O₃. The low-temperature ferroelectric phase also has an orthorhombic crystal structure.     

Dielectric and impedance measurements on (1−x)Ba(Fe1/2Ta1/2)O3-xBa(Zn1/3Ta2/3)O3 ceramics

In this work, ((1−x)Ba(Fe_1/2Ta_1/2)O₃-xBa(Zn_1/3Ta_2/3)O₃), ((1−x)BFT-xBZT) ceramics with x = 0.00–0.12 were synthesized by the solid–state reaction method. X-ray diffraction data revealed that both the powders and ceramics were of a pure-phase cubic perovskite structure. All ceramics showed large dielectric constants. For the x = 0.12 sample, a very high dielectric constant (>20,600) was observed. A lowering in the dielectric loss compared to pure BFT ceramics was observed with the BZT addition. The impedance measurements indicated that BZT has a strong effect on the bulk grain and grain boundary resistance of BFT ceramics. These results are in agreement with the measured dielectric properties. Based on dielectric and impedance results, (1−x)BFT-xBZT ceramics could be of great interest for high performance dielectric materials applications due their giant dielectric constant behavior.     

Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li_1/4Dy_1/4W_1/2)O₃ have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.