Processing Chemistry, Solid Solution Inhomogeneity and Relaxor Behavior

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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.