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Properties of Ferroelectric Perovskite Structures under Non-equilibrium Conditions.

机译：非平衡条件下铁电钙钛矿结构的性质。

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摘要

Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded (BaxSr 1-x)TiO3 (BST) bulk alloys as well as the dynamics of nanodomain walls (nanowalls) in Pb(Zr xTi1-x)O 3 (PZT) ultra-thin films under the driving force of an AC field. Our computations suggest that, for the temperature-graded BST, the polarization responds to the temperature gradient (TG), with the "up" and "down" offset observed in polarization components along the direction of TG, in agreement with the findings from experiments. For the nanowalls in PZT, the dynamics can be described by the damped-harmonic-oscillator model, and we observed a size-driven transition from resonance to relaxational dynamics at a critical thickness of 7.2 nm. The transition originates from the change in the effective mass of a nanowall as a film thickness increases. Some of the findings may find potential applications in various devices, such as thermal sensors, energy converters, or novel memory units.
机译：铁电材料因其令人着迷的特性（如压电效应和热电效应）以及大的介电常数和自发极化而备受关注，这些潜在的信息可用于信息存储。特别地，钙钛矿晶体具有非常简单的晶胞结构和非常丰富的相变图，这使其成为研究最深入的铁电材料之一。在本文中，我们使用有效的哈密顿量，一种基于第一原理的计算技术来研究铁电钙钛矿的有限温度特性。我们研究了温度梯度（BaxSr 1-x）TiO3（BST）块状合金以及Pb（Zr xTi1-x）O 3（PZT）超薄膜在驱动力下的纳米畴壁（nanowalls）的动力学。一个交流场。我们的计算表明，对于温度分级的BST，极化响应于温度梯度（TG），在极化分量沿TG方向观察到的“向上”和“向下”偏移与实验结果一致。对于PZT中的纳米壁，动力学可以通过阻尼谐波振荡器模型来描述，并且我们观察到在7.2 nm的临界厚度下，尺寸从共振到弛豫动力学的尺寸驱动跃迁。过渡源于纳米壁有效质量随膜厚度的增加而变化。一些发现可能会在各种设备中找到潜在的应用，例如热传感器，能量转换器或新型存储单元。

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  • 作者

    Zhang, Qingteng.;

  • 作者单位

    University of South Florida.;

  • 授予单位 University of South Florida.;
  • 学科 Physics General.;Engineering Materials Science.;Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 95 p.
  • 总页数 95
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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