Studies on Self Assembled Nano-Ordered Relaxor Thin Films

点击翻译按钮获取中文摘要

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. ***