(Sr,Ca)TiO3 based multi-functional ceramics with alkaline metallic cations diffusion

Nb⁵⁺-doped (Sr,Ca)TiO₃-based capacitor-varistor ceramics were sintered in a reducing atmosphere, coated with Li⁺, Na⁺, or K⁺ alkaline solution, and annealed in air. The electrical behavior is significantly dependent on the thermal diffusion conditions. The microstructure of (Sr,Ca)TiO₃ 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 TiO₂ with Al, Si. No secondary phase between the grains was observed. The diffusion layer in the range 0.3~2 μm 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 0.4~0.8 eV