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首页> 外文学位 >Toward structure-property correlations in electroceramics: The chemical environment and the electronic structure of grain boundaries in strontium titanate.
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Toward structure-property correlations in electroceramics: The chemical environment and the electronic structure of grain boundaries in strontium titanate.

机译：迈向电陶瓷的结构-特性相关：钛酸锶的化学环境和晶界的电子结构。

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摘要

Electroceramics exhibit macroscopic nonlinear electrical properties owing to the presence of grain boundaries (GBs) and the phenomena associated with them. The mission of the research was to determine aspects of GB structure towards structure-property correlations in SrTiO{dollar}sb3{dollar}, a functional electroceramic. As a first important step the atomic level GB geometric structure was previously determined using both experimental and theoretical methods. This dissertation presents subsequent investigations of the chemical environment and electronic structure of the GBs. The correlations between structural aspects and existing literature on GB properties are also attempted.; With balanced experimental and theoretical investigations of both pristine and impurity incorporated GBs, a consistent picture between the GB segregation and space-charge phenomena was established. Experimental studies involved determination of chemical environment of both bicrystal and polycrystalline GBs using X-ray emission spectroscopy (XES) and electron energy loss spectroscopy (EELS). The nature of segregation, and the aspects of GB electronic structure and electrical activity were determined in connection with impurity incorporation using EELS and electron holography. Studies involved determination of valence and of substitutional behavior of impurities, and direct imaging and quantification of the electrostatic potentials across the GBs. The double-Schottky potential-barrier heights, the local charge density and electrostatic stress field distributions associated with these barriers, and the point defect density at individual GBs were derived directly from the holography results.; Owing to the complexity of the research, only perfect crystal (PC) and previously determined bicrystal GB geometries were considered for theoretical investigations. A density-functional (DF) self-consistent-field (SCF) discrete-variational (DV) embedded cluster calculation method was employed to determine the electronic structure of both pristine and aliovalent impurity incorporated clusters of these geometries. The charge- and spin-densities of states (DOS), Mulliken charge- and spin-electron populations, and charge- and spin-density distributions were determined for different orbitals of the cluster systems. The valence, nature of bonding and charge transfer behavior were also determined for the atoms of the cluster systems. The electronic structure thus determined forms an important bridge between segregation and space-charge phenomena and offers an explanation for the electrical properties exhibited by the GBs.
机译：由于存在晶界（GBs）和与其相关的现象，因此电瓷表现出宏观的非线性电特性。这项研究的任务是确定功能性电瓷SrTiO {dollar} sb3 {dollar}中GB结构与结构性质相关的方面。作为重要的第一步，先前已使用实验和理论方法确定了原子级GB的几何结构。本文提出了GBs的化学环境和电子结构的后续研究。还尝试了结构方面和有关GB特性的现有文献之间的关联。通过对原始的和掺入杂质的GBs进行平衡的实验和理论研究，建立了GB偏析和空间电荷现象之间的一致图景。实验研究涉及使用X射线发射光谱（XES）和电子能量损失光谱（EELS）确定双晶和多晶GB的化学环境。分离的性质，以及GB电子结构和电活性的方面，是结合使用EELS和电子全息图的杂质掺入来确定的。研究涉及确定化合价和杂质的取代行为，以及直接成像和量化GBs上的静电势。直接从全息结果得出双肖特基势垒高度，与这些势垒相关的局部电荷密度和静电应力场分布以及各个GB处的点缺陷密度。由于研究的复杂性，理论研究仅考虑完美晶体（PC）和先前确定的双晶GB几何形状。采用密度泛函（DF）自洽场（SCF）离散变异（DV）嵌入式簇计算方法来确定这些几何形状的原始和含异价杂质结合簇的电子结构。对于簇系统的不同轨道，确定了状态的电荷和自旋密度（DOS），Mulliken电荷和自旋电子种群，以及电荷和自旋密度分布。还确定了簇系统原子的化合价，键的性质和电荷转移行为。如此确定的电子结构形成了隔离和空间电荷现象之间的重要桥梁，并为GBs表现出的电性能提供了解释。

著录项

  • 作者

    Rodrigues, Richard Pascal.;

  • 作者单位

    Northwestern University.;

  • 授予单位 Northwestern University.;
  • 学科 Physics Condensed Matter.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1997
  • 页码 230 p.
  • 总页数 230
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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