钛酸钡基施主掺杂弛豫铁电体介电弥散的唯象分析

弛豫铁电体铁电相变的介电弛豫性涉及外来离子掺杂或原有离子的有序排列, 需要深入理解和有效统一的表征. 针对高浓度施主掺杂在晶粒中产生金属离子缺位, 降低居里温度并引起钛酸钡基铁电材料扩散相变的现象, 分析了高斯型的杂质分布、居里温度分布和金属离子缺位分布的等效对应关系, 得出了在介电常数峰值温区金属离子缺位浓度随温度降低而作用增大的结论, 认为金属离子缺位引起的单极电荷在电场作用下的跳跃运动有可能引起介电弥散和介电损耗. 提出了用‘弛豫度’表征铁电弛豫程度.     

弛豫型铁电体铌镁酸铅陶瓷的玻璃化行为研究

钛酸铅与铌镁酸铅组成比为1:9的固溶体陶瓷是典型的弛豫型铁电体,其介电行为与偶极玻璃的介电行为极为相似,并已将玻璃学中的Vogel-Fulcher关系用于处理其介电常数峰值温度与频率的关系。本文测定了其介电行为随温度的变化,对其微观局域极化行为进行了分析,讨论了其局域极化的产生、增大及冻结过程,研究了弛豫型铁电体与Debye介质、玻璃体的关系和区别。在此基础上,提出了一个更合理的函数关系式,用以表征其介电常数峰值温度与频率的关系,并得出其介电弛豫激活能为0.037eV。实际应用表明,对于弛豫型铁电体,该函数关系较原有Vogel-Fulcher关系更有效。 关键词：     

玻璃化液体中构型熵与展宽弛豫函数关系的研究

运用Adam Gibbs关于构型重排区域的构型熵理论和极值动力学模型得到的弛豫时间的理论公式,提出了KWW型弛豫函数中的非指数展宽因子等于液体中构型重排区域的相对构型熵;并与一个构型重排区域内构型变换的临界分子数成反比,从而赋予了展宽因子新的关于玻璃化结构的物理意义,建立了结构弛豫与构型熵之间的关联.为了消除Vogel Fulcher Tamann方程拟合粘度实验数据在高温区的偏差,用温度的高阶项修正展宽因子与温度的关系,其结果在低于200K时符合得很好,其修正项等效于等压与等容热容量之差对构型熵的修正.     

核壳结构对弛豫铁电体介电行为的影响

介电弥散和介电隔离率的温度非线性关系是弛豫铁电体的主要特征. 通过对掺杂成分以线性梯度递减的核壳结构进行热力学函数分析, 认为核壳结构能够在低温区保持较高的介电常数, 但不能导致介电隔离率与温度的非线性关系. 通过对不同浓度掺杂的铁电体扩散相变的比较, 认为掺杂浓度会影响晶粒掺杂成分的不均匀性, 在较宽的分布条件下会导致介电隔离率与温度的非线性关系. 因而在介电常数的峰值温度区域, 顺电相与铁电相的晶粒共存. 温度变化会影响两相比例及铁电畴的变化, 从而导致弛豫铁电体的介电弥散性. 核壳结构会增大介电弥散性. 铁电陶瓷的掺杂物种类、掺杂物浓度和烧结温度均会影响核壳结构的成分不均匀性和介电弥散性.     

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     

弛豫铁电体的键能与配位数模型

基于一定浓度的杂质会在钛酸钡型铁电体中导致键能与配位数的高斯型分布原理,利用键能与配位数起伏模型导出了介电峰温与测量频率的关系.当键能和配位数的相对起伏接近时,其关系呈现出一般弛豫铁电体所普遍具有的Vogel-Fulcher函数形式,且冻结温度仅与键能的相对起伏和激活能有关.并由此解释了低掺杂浓度下杂质均匀分布导致弥散性的机理和超过临界浓度时的弛豫铁电性的机理.同时提出,杂质替代对畴的形成和生长所产生的强烈抑制作用及微畴化是实现键能起伏与配位数起伏一致的来源.     

聚合物介电弛豫的温度特性

运用极限的概率模型和Ngai的耦合概念,导出了聚合物介电弛豫的KohlrauschWilliamsWatts(KWW)方程(t)=exp[-(tτ)β],证明了弛豫的能量势垒为Ngai的活化能量E.由β的温度关系推出了适用于聚合物的WilliamsLandelFerry方程和过冷液体的VogelTammannFulcher方程,特别是提出了由聚合物的β(T)可导出弛豫时间的温度函数.认为KWW行为由单个衰减单元产生,幂律行为由局部区域内多个衰减单元的协同衰减造成.将活化能量E引入热刺激电流公式,得到了可通过改变升温速率测量β(T)的公式. 关键词： 介电弛豫 聚合物 极限概率模型 KWW方程     

偏氟乙烯/三氟乙烯铁电共聚物的非晶介电弛豫

用溶液成膜、液氮淬火、熔融慢冷和热处理4种方法制得不同结晶度的VDF/TrFE共聚物试样。在已改进的介电弛豫谱仪(精度由原来的1％提高到2‰)上测得复数介电常数。从结晶度为20％的淬火试样室温以下的介电频率谱中发现了非晶介电弛豫,并由此得到了玻璃化温度与共聚物组分含量的关系。 关键词：     

自组织临界的OFC模型在聚丙烯介电弛豫中的应用

将自组织临界中OFC模型的能量传递概念及相关参量α引入极值动力学模型,得到了同时与KWW方程和幂律均相关的介电弛豫的函数关系。用时域介电谱方法测量了聚丙烯在-15～90℃慢极化电荷的释放过程,结果显示：在较低温度,弛豫为幂律;在较高温度,弛豫随时间的增加从幂律过渡到KWW关系。理论分析与实验结果基本一致,由此可知KWW方程的参量β反映了外界温度对材料弛豫单元物影响;参量α反映了能量传递的大小及温度的影响,当β较小或α较大时,弛豫的幂律关系较为明显。     

嵌埋Ni颗粒的BaTiO_3/SrTiO_3薄膜的相变特性

采用高温X射线原位衍射和变温介电谱对SrTiO3基底上外延生长的BaTiO3(嵌埋Ni颗粒)薄膜进行了相变特性分析。从X射线衍射和介电谱的分析结果得出,BaTiO3的相变温度点转变为弥散的温度区间。在这个弥散的相变温度区间内,由于基底和薄膜之间的失配,以及嵌埋Ni颗粒的应力作用,薄膜的介电响应弥散剧烈,并偏离德拜弛豫。分析Cole-Cole图获知,BaTiO3薄膜在四方相转变为立方相的相变过程中同时存在几种极化机制,在高温状态下介电损耗随温度增大而增大。降温过程中,薄膜没有立即恢复四方相,可能是基底和Ni颗粒的共同作用影响了相变弛豫。     

Monte Carlo simulation on dielectric relaxation and dipole cluster state in relaxor ferroelectrics

The Ginzburg--Landau theory on ferroelectrics with random field induced by dipole defects is studied by using Monte Carlo simulation, in order to investigate the dipole configuration and the dielectric relaxation of relaxor ferroelectrics. With the increase of random field, the dipole configuration evolves from the long-range ferroelectric order into the coexistence of short-range dipole-clusters and less polarized matrix. The dipole-cluster phase above the transition temperature and superparaelectric fluctuations far below this temperature are identified for the relaxor ferroelectrics. We investigate the frequency dispersion and the time-domain spectrum of the dielectric relaxation, demonstrating the Vogel--Fulcher relationship and the multi-peaked time-domain distribution of the dielectric relaxation.     

Relationship between local structure and relaxor behavior in perovskite oxides

Despite intensive investigations over the past five decades, the microscopic origins of the fascinating dielectric properties of ABO3 relaxor ferroelectrics are currently poorly understood. Here, we show that the frequency dispersion that is the hallmark of relaxor behavior is quantitatively related to the crystal chemical characteristics of the solid solution. Density functional theory is used in conjunction with experimental determination of cation arrangement to identify the 0 K structural motifs. These are then used to parametrize a simple phenomenological Landau theory that predicts the universal dependence of frequency dispersion on the solid solution cation arrangement and off-center cation displacements.     

Giant dielectric permittivity observed in pb-based perovskite ferroelectrics

Giant dielectric permittivity was observed in La-modified PbTiO (3) (PLT) with A-site vacancy. The observed values of PLT with A-site vacancy are 1 order of magnitude larger than those of relaxor ferroelectrics. The giant relative dielectric permittivity, coupled with a low dielectric loss (tandelta approximately 0.03) of the PLT, potentially makes it one of the most promising materials for numerous modern technological applications.     

Relaxor behavior of SrTiO3-LiNbO3 solid solutions

Ceramic samples of (1 ? x)SrTiO₃-xLiNbO₃ (0 ≤ x ≤ 0.05) solid solutions are synthesized. The dielectric and acoustic properties of the solid solutions are studied in the temperature range from 15 to 300 K. It is revealed that the polar state characterized by the dispersion of the permittivity and the dielectric hysteresis occurs at low temperatures. The results obtained are discussed within the concept of relaxor ferroelectrics.     

Neutral-ionic phase separation and one-dimensional ferroelectricity in organic relaxors

Microscopic phase segregation by chemical doping and resultant anomalous dielectric response have been investigated for tetrathiafulvalene-p-chloranil complex doped with trichloro-p-benzoquinone ( QCl3). Beyond a critical QCl3 content, the system shows a behavior of relaxor ferroelectrics, as characterized by strong frequency dispersion and a rounded peak shape of gigantic dielectric susceptibility. The relaxor phase arises from one-dimensional ferroelectricity, as evidenced by a diffuse x-ray scattering, in which interchain ferroelectric coupling associated with neutral-ionic transition is interrupted by impurity-generated neutral microclusters.