Texture and Anisotropy in Ceramics
A central focus of ceramic research in recent years has been microstructural design employing integrated consideration of processing-property relationships. Despite the prevalence of research on composites or multiphase ceramics and ceramics with special microstructural features (e.g. bridging grains in structural ceramics), few authors provide detailed quantitative information on size, shape, spatial, and orientational descriptions of the materials investigated.
The MSE research program on preferred orientation in ceramics is the leading program on describing preferred orientation evolution during conventional and novel processing approaches; measuring ceramic textures via x-ray diffraction, neutron diffraction and stereology; quantifying and modeling property anisotropy arising from preferred orientation and demonstrating strategies for component designs integrating textures for property optimization. Besides optimizing fracture toughness or strengths in ceramics via preferred orientation, anisotropies in thermal expansion, thermal conductivity, electrical conductivity, superconductivity, piezoelectricity, ferroelectricity and optical properties have all been exploited. Rarely, however, have these properties been precisely correlated with textures in other than qualitative approaches.
MSE researchers have demonstrated anisotropies in textured structural and electronic ceramics with directional property differences as high as a factor of three. Since ceramists and texture researchers have operated in almost mutually exclusive arenas, the Purdue MSE program has also adopted a role as a liaison between scientists in both research areas.
Low Temperature Processing of Ceramic and Polymer/Ceramic Thin Films
Many applications will benefit from low temperature (<100°C) processing routes to ceramic materials. For example: dielectric ceramics may be incorporated into microelectronics manufacturing processes without degrading metallizations, and ceramics may be coprocessed with polymers for high strength capacitors or abrasion resistant coatings. Hydrothermal processing is a route to ceramics below 100°C, involving the formation of crystalline material from reactants in an aqueous medium. It may be used to fabricate functional ceramics like BaTiO3.
The research effort seeks to develop routes to control film morphology via an understanding of hydrothermal growth mechanisms. Thin layers of titanium metal-organic liquid precursors are deposited onto substrates by spin coating, and reacted with aqueous solutions of dissolved solids below 100°C to process films of BaTiO3, SrTiO3 and (Ba,Sr)TiO3. Seeding is used to control film nucleation, with nanometer-size powders (BaTiO3, SrTiO3 or (Ba,Sr)TiO3) as seeds for polycrystalline films, and oriented single crystals of SrTiO3 to grow epitaxial films of SrTiO3 and BaTiO3. Chemical and microstructural characterization techniques, and dielectric property measurements, are used to evaluate film composition, structure and properties.