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    Dielectric nonlinearity of ferroelectrics.

    机译:铁电体的介电非线性。

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    摘要

    The ac field dependence of the dielectric constant and first order reversal curves (FORC) distribution were employed to quantify the effect of dielectric thickness, grain size, oxygen vacancy concentration, and microstructural heterogeneity on the dielectric nonlinearity of PbZr0.52Ti0.48O 3 thin films and BaTiO3-based ceramics on a wide electric field range. With the FORC distribution, the dielectric properties were calculated using Preisach model.;The FORC distribution of PbZr0.52Ti0.48O3 thin films was characterized as a function of film thickness. It was found that the thickness dependence of the small field dielectric constant is due primarily to differences in the domain wall contributions to the properties. The irreversible FORC distribution decreased and the switching fields increased as the thickness decreased. Prediction of the polarization-electric field curves and the ac field dependence of the dielectric constant were found to give a good fit to the experimental results. Some discrepancies remain in the high field dielectric constant, probably caused by its definition.;The dielectric nonlinearity of BaTiO3 ceramics with grain sizes from 1.2 to 76 microm was investigated. Defect dipoles in samples with large grains led to pinching of minor polarization-electric field loops as well as a threshold field in the ac field dependence of the dielectric constant and loss. For samples with small grains, a sublinear ac field dependence was observed. The irreversible FORC distributions characterizing the responses showed two strong and narrow peaks for large-grained samples and a weak, broad peak centered near the origin for samples with small grains. As the grain size decreased, the reversible FORC distribution at zero-bias field increased. No grain size dependence of the reversible FORC distributions was observed at high dc electric fields. These results indicate that the grain size dependence of the small field dielectric constant is attributable to a domain wall contribution and long-range domain wall motion suppressed while short-range domain wall motion enhanced as the grain size decreased.;The effect of the oxygen vacancies on the dielectric nonlinearity of formulated and undoped BaTiO3 ceramics was investigated by changing oxygen partial pressure during firing. For the formulated ceramics, the dielectric constant of both oxygen and air fired samples increased almost linearly with the amplitude of the ac driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sub-linear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sub-linearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move.;FORC distributions as well as the ac field dependence of the dielectric constant were investigated for model BaTiO3-based multilayer ceramic capacitors with dielectric layer thicknesses from 2.2 microm to 8.6 microm and those in which the grain size of the dielectrics varied from 0.28 microm to 0.39 microm while the layer thickness was held constant. In both cases, core-shell microstructures were observed. It was found that as the dielectric thickness decreased, the small and high electric field dielectric constants decreased, as did the peaks near the origin in the irreversible and reversible parts of the FORC distribution. The reversible FORC distributions of all the parts did not converge at high bias. These results indicate that the thickness dependence is attributable to a low dielectric constant interfacial layer and/or Schottky depletion layer at dielectric-electrode interfaces.;It was also found that the high field dielectric constant, the peak in the irreversible FORC distribution at the origin, and the reversible FORC distribution at zero bias decreased as grain size decreased, as was observed for the undoped ceramics. The reversible FORC distribution of all the parts converged at high biases, indicating the grain size dependence was influenced by domain wall contributions. Dielectric contributions from the core and shell were estimated based on the temperature dependence of the permittivity. Not unexpectedly, the relative response of the core decreased while that of the shell increased as the grain size decreased. A Preisach model using the measured FORC distribution gave a good fit to the experimental polarization-electric field loops as a function of grain size and dielectric layer thickness.
    机译:用介电常数和一阶反转曲线(FORC)分布的交流场依赖性来量化介电厚度,晶粒尺寸,氧空位浓度和微观结构异质性对PbZr0.52Ti0.48O 3薄膜介电非线性的影响以及在宽电场范围内的BaTiO3基陶瓷。利用Preisach模型计算了FORC的分布。表征了PbZr0.52Ti0.48O3薄膜的FORC分布与膜厚的关系。发现小场介电常数的厚度依赖性主要是由于畴壁对性能的??贡献的差异所致。随着厚度的减小,不可逆的FORC分布减小,开关场增大。发现极化-电场曲线的预测和介电常数的交流场依赖性与实验结果非常吻合。高场介电常数仍存在一些差异,可能是由于其定义所致。;研究了粒径为1.2至76微米的BaTiO3陶瓷的介电非线性。具有大晶粒的样品中的缺陷偶极子导致夹挤较小的极化电场环路,以及介电常数和损耗在ac场中的阈值场。对于具有小晶粒的样品,观察到亚线性交流场依赖性。表征响应的不可逆的FORC分布对于大颗粒样品显示两个强峰和窄峰,对于小晶粒样品,在中心附近形成一个弱而宽的峰。随着晶粒尺寸的减小,零偏场的可逆FORC分布增加。在高直流电场下未观察到可逆FORC分布的晶粒尺寸依赖性。这些结果表明,小场介电常数对晶粒尺寸的依赖性可归因于畴壁的贡献和长程畴壁运动的抑制,而短程畴壁运动随晶粒尺寸的减小而增强。;氧空位的影响通过改变烧成过程中的氧分压,研究了配制和未掺杂的BaTiO3陶瓷的介电非线性。对于配制的陶瓷,氧气和空气样品的介电常数几乎随交流驱动场的幅度线性增加。在还原性气氛中烧结的配制成配方的BaTiO3样品,随着交流场振幅的出现,介电常数出现亚线性增加。对于未掺杂的BaTiO3陶瓷,在烧制过程中,介电常数在较宽的氧气分压范围内呈亚线性增加。对于配制的陶瓷,提出了壳区域中的掺杂剂-氧空位缺陷偶极子解释了介电常数的场依赖性的曲率。这些缺陷似乎在势能分布中增加了弱钉扎中心的浓度,畴壁通过该势能分布进行了研究。研究了具有介电层厚度的基于BaTiO3的多层陶瓷电容器模型的FORC分布以及介电常数的交流场依赖性。从2.2微米到8.6微米,以及其中电介质的晶粒尺寸从0.28微米到0.39微米变化而层厚度保持恒定的那些。在这两种情况下,都观察到了核壳结构。发现随着介电层厚度的减小,小的和高电场介电常数会减小,FORC分布的不可逆和可逆部分的原点附近的峰也会减小。所有零件的可逆FORC分布都没有在高偏差下收敛。这些结果表明厚度依赖性归因于介电电极界面处的低介电常数界面层和/或肖特基耗尽层。;还发现高场介电常数是在原点处不可逆的FORC分布的峰值如未掺杂的陶瓷所观察到的,零偏压下可逆的FORC分布随晶粒尺寸的减小而减小。所有零件的可逆FORC分布在高偏差下会聚,这表明晶粒尺寸依赖性受畴壁贡献的影响?;诮榈绯J晕露鹊囊览敌?,估算了核和壳的介电贡献。并不出乎意料的是,随着晶粒尺寸的减小,核的相对响应下降而壳的相对响应上升。使用测得的FORC分布的Preisach模型与晶粒尺寸和介电层厚度的函数非常吻合了实验极化电场回路。

    著录项

    • 作者

      Fujii, Ichiro.;

    • 作者单位

      The Pennsylvania State University.;

    • 授予单位 The Pennsylvania State University.;
    • 学科 Engineering, Materials Science.
    • 学位 Ph.D.
    • 年度 2010
    • 页码 209 p.
    • 总页数 209
    • 原文格式 PDF
    • 正文语种 eng
    • 中图分类 ;
    • 原文服务方 国家工程技术数字图书馆
    • 关键词

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