Processing Chemistry, Solid Solution Inhomogeneity and Relaxor Behavior

以前已经用溶胶-凝胶技术制备了许多固溶体氧化物。这种方法的优点之一是最终产品的化学均匀性。但是，有理由相信，在任何情况下，产物都不会是随机的固溶体。固溶体体系中成分不均匀性的存在会对材料的性质产生重要的影响。在这项研究中，铁电材料的样品将使用已发表的溶胶-凝胶方法制备。产品将使用分析电子显微镜和固态核磁共振相结合的方法进行检查。对分布函数（pdf）将从x射线和/或中子散射数据计算。这种方法应该提供足够的证据来评估样品中单个晶体的成分均匀性，从而评估现有的溶胶-凝胶化学产生随机固溶体的能力。由于溶胶-凝胶化学被广泛应用于制备氧化物，任何获得的关于生产随机产物的技术的信息都与一个大的领域有关。然后利用溶胶-凝胶化学来有意地制备铁电体的非随机固溶体。已知铁电体中~ 5-10 nm长度范围内的成分和/或结构波动会在许多系统中引起弛豫行为。人们认为，通过在通常不显示弛豫性质的固溶体中引入成分波动可以诱导这种行为。将使用分析电子显微镜和从x射线和/或中子散射数据计算的pdf来评估产品的成分均匀性。这些实验将通过测量材料的介电特性作为频率和温度的函数来支持。这项工作将有助于理解产生松弛行为所需的确切条件，并有可能产生有用的新材料。用溶液法合成陶瓷已实践多年。在过去的10 - 15年里，由于这种方法所提供的好处得到了广泛的认识，这种路线一直是大量研究工作的主题。这些可能包括：1)低加工温度；2)薄膜和纤维制造；3)对陶瓷中杂质水平的良好控制；4)最终产品中的化学均匀性。组分均匀性等特性显然对某些材料的性能很重要。本研究将探讨溶胶-凝胶法制备铁电固溶体的加工化学、固溶体不均匀性和介电性能之间的关系。提出了一种简单的策略来引入可控量的不均匀性到固溶体中。通过控制固溶体铁电的非均匀性水平，可以调整材料的介电性能。

Abstract 9623890 Wilkinson Many solid solution oxides have previously been prepared using sol-gel techniques. One of the often stated advantages of this approach is the chemical homogeneity of the end product. However, there is reason to believe that the products will not be random solid solutions under all circumstances. The existence of compositional inhomogeneities in solid solution systems can have important consequences for the properties of the material. In this research, samples of the ferroelectrics materials will be prepared using published sol-gel procedures. The products will be examined using a combination of analytical electron microscopy and solid state NMR. Pair distribution functions (PDFs) will be calculated from X-ray and/or neutron scattering data. This approach should provide enough evidence to assess the compositional homogeneity of individual crystallites within a sample and, hence, the ability of existing sol-gel chemistry to produce random solid solutions. As sol-gel chemistry is widely used for preparing oxides any information gained regarding the techniques ability to produce compositionally random products is relevant to a large field. Sol-gel chemistry will then be exploited to deliberately prepare non-random solid solutions of the ferroelectrics. Compositional and/or structural fluctuations on ~ 5-10 nm lengths scale within ferroelectrics are known to give rise to relaxor behavior in many systems. It is thought that by introducing compositional fluctuations into solid solutions that do not normally display relaxor properties such behavior can be induced. The compositional homogeneity of the products will be assessed using analytical electron microscopy and PDFs calculated from X-ray and/or neutron scattering data. These experiments will be supported by measurements of the materials dielectric properties as a function of frequency and temperature. This work will aid the understanding of exactly what is required to produce relaxor beh avior and has the potential to produce useful new materials. %%% The synthesis of ceramics using solution processing has been practiced for many years. Such routes have been the subject of a vast research effort in the last 10 - 15 years due to the wide spread realization of the benefits offered by this approach. These potentially include, i) low processing temperatures, ii) thin film and fiber fabrication, iii) good control over impurity levels in the ceramic and, iv) chemical homogeneity in the end product. Characteristics such as compositional homogeneity are clearly important to the properties of some materials. This research will examine the relationship between processing chemistry, solid solution inhomogeneity and dielectric properties for some sol-gel produced ferroelectric solid solutions. A simple strategy is suggested for introducing controllable amounts of inhomogeneity into the solid solution. By controlling the level of inhomogeneity in a solid solution ferroelectric it may be possible to tailor the dielectric properties of the material.