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|Title:||Interfacial Phenomena in Electrical Ceramics and the Design and Fabrication of Semiconducting Ceramics|
|Author(s):||Amarakoon, Vasantha Rohana Wijewardena|
|Department / Program:||Ceramics Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Interfaces and interfacial phenomena exert a major influence on the behaviour of materials and hence dominate their utility in many applications. It has been recognized that the advantages offered by electrical ceramics are inherently connected with their microstructure; and the properties they control, depend critically on the boundary conditions existing at internal surfaces or grain boundaries. In this thesis, the design, fabrication, and characterization of semiconducting ceramics for applications such as photoassisted electrolysis of water; SrTiO(,3) based internal boundary layer capacitors; positive temperature coefficient of resistance thermistors; and ferrites have been considered.
Heterostructure electrodes consisting of corrosion resistant wide band gap materials and efficient sunlight absorbing low band gap semiconductors, were designed by material selection according to compatibility with respect to crystal structure, thermal expansion and energy band structure, so as to avoid problems such as corrosion, as well as any obstruction of transport of minority and majority carriers through the interface.
WO(,3) doped SrTiO(,3) IBL capacitors with stable dielectric properties, processed by a single firing operation in air, resulted in dense, uniform small grain size products with possible applicability in thin-multilayer capacitors. Bismuth doped SrTiO(,3) IBL capacitors were found to consist of non-uniform microstructures.
Interrelationships that exist between chemical composition, processing conditions, microstructure development and electrical properties were determined for BaTiO(,3) PTCR thermistors. SAES analysis of surfaces fractured in vacuum (i.e., 10('-10) torr), determined the presence of barium excess compositions at grain boundary regions with an associated increase in the PTCR effect. The experimental observations are in conflict with present theories which invoke the presence of barium vacancies at grain boundaries to control the resistivity jump at the Curie temperature.
The effects of post sintering thermal treatments on the electrical properties of MnZn ferrites were determined. Samples quenched (i.e., cooled quickly from sintering temperature) were found to be resistive and did not contain any additional phases. Samples, slowly cooled in air, were found to contain additional Mn-rich phases, and therefore Fe(,3)O(,4) rich MnFe(,2)O(,4), which correlated with high electrical conductivities and increased Curie points. Addition of CaO and SiO(,2) improved the density but not the resistivity of MnZn ferrites.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2014-12-16|