Studies on Self Assembled Nano-Ordered Relaxor Thin Films

该项目旨在更好地了解一类特殊的复合氧化物材料，称为弛豫体，虽然本质上是铁电体，但在相变行为和介电性能方面与普通铁电体有很大不同。因为这些材料具有非常高的介电、压电和电光特性系数，所以它们对于电子和微机电（MEM）器件是有利的。然而，纳米尺度的有序性及其对性能的影响还没有得到很好的确定。该方法涉及高应变弛豫铁电体的有序纳米区域的系统研究。在精细结构尺度上，上述弛豫材料包含分散在三维无序基质中的自组装纳米级有序区域。由于这些区域的典型尺寸，如通过透射电子显微镜所研究的，是2-5 nm的量级，它们的结构和尺寸的任何变化都会影响相关的声子频率和半宽度。因此，选择拉曼散射作为探测其纳米级结构和动态特征的主要工具。将使用不同的退火条件、掺杂和组成来制备具有各种尺寸的有序纳米区域的弛豫材料。溶胶-凝胶工艺将用于生长陶瓷和薄膜形式的上述弛豫材料。还将使用脉冲激光沉积（PLD）技术制备薄膜。显微拉曼散射（在可见光和紫外线区域）将被用来评估纳米有序区域的基本特征。这些研究预计将有助于建立最近提出的模型，即空间电荷和电荷平衡随机层模型的适用性，用于解释1：2 B-位点化合物中1：1纳米有序区域的发生。材料的品质因数，其中包括极化滞后和电场对光学，压电和介电性能的影响，将进行评估和相关的微观结构和纳米级的订购。这些研究也有望帮助了解衬底和生长条件如何改变薄膜结构（应变，晶粒尺寸，纳米有序和不均匀性），从而影响压电，介电和铁电性能。%%% 该项目涉及材料科学领域的基础研究问题，具有重要的技术相关性。除了获得更大的基本理解，有用的输出预期从该项目的基本信息，这将提供指导方针，设计高效的铁电薄膜器件应用所需的微结构。该项目的一个重要特点是研究和教育的一体化，并培养学生作为研究人员的基本材料合成，加工和表征技术的技能。***

This project aims for greater understanding of a special class of complex oxide materials, known as relaxors, which though ferroelectric in nature, differ enormously from the normal ferroelectrics in terms of phase transition behavior and dielectric properties. Because these materials possess very high dielectric, piezoelectric, and electro-optic property coefficients, they are advantageous for electronic and micro-eletromechanical (MEM) devices. Nano-scale ordering and its effect on properties are not well established, however. The approach involves a systematic study of ordered nano-regions of high strain relaxor ferroelectrics. On a fine structural scale, the above relaxor materials contain self-assembled nanoscale ordered regions dispersed in a three-dimensional disordered matrix. Since the typical sizes of these regions, as studied by transmission electron microscopy, are of the order of 2-5 nm, any variation in their structure and size affects associated phonon frequencies and half widths. Raman scattering is, therefore selected as a primary tool to probe their nanoscale structural and dynamic features. Relaxor materials with various sizes of ordered nano-regions will be prepared using different annealing conditions, doping, and composition. Sol-gel processing will be used to grow the above relaxor materials in both ceramic and thin film forms. Thin films will also be prepared using a pulsed laser deposition (PLD) technique. Micro-Raman scattering (in visible and ultraviolet regions) will be utilized to assess basic features of the nano-ordered regions. These studies are expected to assist in establishing the applicability of recently proposed models, namely, space charge and charge balance random layer models, for explaining the occurrence of 1:1 nano ordered regions in 1:2 B-site compounds. The material figure of merit, which includes polarization hysteresis and electric field effects on the optical, piezoelectric, and dielectric properties, will be evaluated and correlated to microstructure and nano-scale ordering. These studies are also expected to help understand how substrate and growth conditions alter film structure (strain, grain size, nano-ordering, and inhomogeneity) and thereby affect piezoelectric, dielectric and ferroelectric properties. %%% This project addresses basic research issues in a topical area of materials science with significant technological relevance. Beyond gaining greater fundamental understanding, useful outputs expected from the project are basic information which will provide guidelines for the design of efficient ferroelectric thin films with desirable microstructures for device applications. An important feature of the project is the integration of research and education, and the training of students as researchers with skills in fundamental materials synthesis, processing, and characterization techniques. ***