MICROSTRUCTURE AND GRAIN-BOUNDARY STRUCTURE OF NA-DIFFUSED (SR,CA)TIO3 CAPACITOR VARISTOR CERAMICS()

The microstructure of (Sr,Ca)TiO3 capacitor-varistor materials has bee n investigated by employing electron microscopy techniques (TEM, STEM, HREM, EDX, and EPA). The material is found to contain (Sr,Ca)TiO3 gra ins (similar to 30 mu m) having perovskite crystal structure with doma ins, a Na+-diffused layer at the grain boundaries which is dependent o n thermal diffusion conditions, and multiple-grain junctions in which the TinO2n-1 Magneli phase coexists with an amorphous intergranular ph ase. In addition, wider grain boundaries (10-30 nm), thin grain bounda ries (similar to 1 nm), and clean grain boundaries which are free from intergranular phase were observed, and the effects of different grain boundaries on the diffusion of Na+ are discussed.