Effect of BaO and SiO2 addition on PTCR BaTiO3 ceramics

The influence of Ba-excess and liquid phase sintering with SiO2 on the elec trical conduction and microstructure in PTCR BaTiO3 has been investigated. Dense (95-96%), small grain (5-10 mu m) PTCR materials were obtained in Ba- excess (Ba/Ti = 1.006) BaTiO3. The materials exhibit low room temperature r esistivity rho(RT) (10(0)-10(2) Omega . cm) and high PTCR respond (more tha n 5 orders). Solid state sintering was found to inhabit the semiconducting and PTCR behavior in Ba-excess materials. Liquid phase sintering, using SiO 2 in the Ba-excess BaTiO3, resulted in low rho(RT) and significant PTCR res ponse. Through domain observation, interior "Polaron deficient zones" were found in samples which exhibit limited liquid phase sintering, leading to n on-uniform directional domains and low charge carrier mobility. Proper cont rol of the SiO2 concentration was found critical for obtaining uniform dire ctional domain microstructures and low rho(RT). (C) 1999 Kluwer Academic Pu blishers.