Interfacial Segregation in Perovskites: III, Microstructure and Electrical Properties

A model is proposed to relate segregation of dopants with the development of fine ceramic microstructures and electrical properties in polycrystalline donor‐doped BaTiO 3 . As the average dopant concentration is increased, the dopant concentration at the grain boundary increases compared with the bulk. This has two important effects: (1) dopant incorporation at the grain boundary shifts from electronic to vacancy compensation and the formation of high‐resistive layers, and (2) grain‐boundary mobility is impeded and grain growth retarded with increased dopant additions. Thus, for high dopant concentrations, donor‐doped BaTiO 3 becomes insulating. The model discusses in detail the nonequilibrium heterogeneous defect chemistry as a function of thermal‐processing and accounts for barrier layer phenomena.