Size Effects in Ferroic Solids

小行星9223847 该奖项是宾夕法尼亚州立大学一个新材料研究小组的初始资金，该小组的主题是铁性固体的尺寸效应。 氧化物铁电体中的标度现象正在从理论和实验上进行研究。 重点放在确定以下四个制度的临界尺寸：（1）大颗粒，每个都包含许多畴壁，其数量随着颗粒尺寸的减小而减少，（2）包含单个畴的颗粒，（3）小于单个畴的颗粒尺寸，（4）纳米尺寸尺度的颗粒。 材料系统的选择是铁电体，铁弹，和二次铁电。 目标是确定每个系统的临界颗粒尺寸，其中材料及其行为从体行为转变为单畴行为，再转变为玻璃状和非铁电行为。 实验计划包括制备细颗粒粉末和陶瓷/聚合物以及陶瓷/陶瓷复合材料的薄膜形式;使用热分析、X射线衍射、拉曼光谱、电子显微镜和椭圆偏振光谱表征颗粒/颗粒微观结构、畴结构、相变和临界尺寸;测量介电常数、弹性，作为施加场、温度和频率的函数。 理论部分基于Landau-Ginsburg-Devonshire形式主义。 体积，外表面，和内部接口（晶界和畴壁）的影响被认为是。 铁电晶体具有畴壁，畴壁可以通过电场（铁电体）、磁场（铁磁体）、机械力和磁场（铁磁体）移动。 应力（铁弹性），或一些涉及 前三者的组合（二次铁性）。 这些材料 用作换能器、电容器、变压器、传感器和致动器， 这是因为畴壁对压电性、介电常数、磁导率、弹性柔量和其它特性系数的贡献较大。 对尺寸效应的基本理解对于 这些设备的发展，这是越来越小的形式， 薄膜、纤维填充复合材料和多层陶瓷， 亚微米颗粒大小。

9223847 Newnham This award is the initial funding for a new Materials Research Group at the Pennsylvania State University on the topic of size effects in ferroic solids. Scaling phenomena in representative oxide ferroics are being investigated theoretically and experimentally. Emphasis is being placed on determining the critical sizes for the following four regimes: (1) large particles that each contain many domain walls which reduce in number as the particle size decreases, (2) particles that contain a single domain, (3) particle sizes smaller than a single domain, (4) particles in the nanometer size scale. The material systems of choice are ferroelectrics, ferroelastics, and secondary ferroics. The goal is to determine the critical particle sizes for each system where the material and its behavior transitions from bulk behavior to single domain behavior to glass-like, and non-ferroelectric behavior. The experimental program involves preparation of fine-grain powders plus ceramic/polymeric, and ceramic/ceramic composite materials in the form of thin films; characterization of the particle/grain microstructure, domain configurations, phase transformations, and critical sizes using thermal analysis, x-ray diffraction, Raman spectroscopy, electron microscopy, and spectroscopic ellipsometry; measurement of permittivity, elasticity, as a function of applied field, temperature, and frequency. The theory component is based on the Landau-Ginsburg-Devonshire formalism. The effects of volume, external surfaces, and internal interfaces (both grain boundaries and domain walls) are considered. Ferroic crystals have domain walls which can be moved by electric fields (ferroelectrics), magnetic fields (ferromagnets), mechanical stress (ferroelastics), or some higher order phenomena involving a combination of the first three (secondary ferroics). These materials are used as transducers, capacators, transformers, sensors, and actuators, because of the lar ge contribution that domain walls make to piezoelectricity, permittivity, permeability, elastic compliance, and other property coefficients. A basic understanding of size effects is critical to the development of these devices, which are being made smaller in the form of thin films, fiber-filled composites, and multilayer ceramics with submicron grain sizes.