Characterization of Internal Boundary Layer Capacitors Based Upon Barium-Titanate and Strontium-Titanate

103 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.The properties of polycrystalline electrical ceramics are greatly influenced by the electrical and mechanical boundary conditions existing at grain and phase boundaries. The dielectric properties of internal boundary layer capacitor are directly related to their microstructure, in which semiconducting grains are surrounded by continuously connected thin insulating boundaries. Heterogeneous distributions in resistivity, between conducting grains and insulating boundaries, results in thin, interfacial space charge layers of high capacitance and high apparent dielectric constant.The nature of ceramic microstructure and the electrical properties of individual grains and junctions was determined by STEM, microprobe analysis and microscale electrical measurements. The chemical compositions of the resistive boundary regions were different from those of the grains. Additives were concentrated in the boundary regions, forming resistive layers. Limited diffusion of the counterdopants into the grain subsurface formed an interfacial compensation layer between the insulating intergranular layer and the semiconducting grains. The electrical behavior of this intermediate layer was found to be similar to that of a depletion layer.Ceramic microstructures were approximated by a three-layer n-c-i-c-n model and representative equivalent circuit, which was used to explain the voltage dependence of the dielectric constant and dispersion behavior. Calculated properties were in good agreement with experimental values. Fine grain microstructures developed by liquid phase sintering techniques, were suitable for high dielectric constant multilayer capacitors, based upon internal boundary layer phenomena, and these capacitors had stable dielectric characteristics.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD