(Sr,Ca)TiO/sub 3/ based multi-functional ceramics with alkaline metallic cations diffusion

Nb/sup 5+/-doped (Sr,Ca)TiO/sub 3/-based capacitor-varistor ceramics were sintered in a reducing atmosphere, coated with Li/sup +/, Na/sup +/, or K/sup +/ alkaline solution, and annealed in air. The electrical behavior is significantly dependent on the thermal diffusion conditions. The microstructure of (Sr,Ca)TiO/sub 3/ based ceramics is composed of grains, a diffusion layer at the grain boundaries, and a precipitated small crystal at triple points, such as the Magneli phase of rutile TiO/sub 2/ with Al, Si. No secondary phase between the grains was observed. The diffusion layer in the range 0.3/spl sim/2 /spl mu/m is considered to be caused by the diffusion of alkaline metallic cation and oxygen chemisorption on grain surfaces and to be significantly dependent on thermal diffusion conditions. A back-to-back Schottky barrier sandwich model is presented. Based on this model, the barrier height is estimated from simulation of the C-V characteristics to be about 0.4/spl sim/0.8 eV.<
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