Internal Oxidation of Ce 3+ ‐BaTiO 3 Solid Solutions

The reoxidation process in highly Ce 3+ ‐doped BaTiO 3 ceramics was studied using TEM. Samples of two different types of solid solutions, Ba 1−X Ce 3+ X Ti 1−X/4 ( V  Ti ) X/4 O 3 and Ba 1−X Ce 3+ X Ti 4+ 1− X Ti 3+ X O 3 , were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce 3+ and Ti 3+ , fluorite CeO 2 and monoclinic Ba 6 Ti 17 O 40 phases were precipitated in the perovskite matrix. In Ba 1−X Ce 3+ X Ti 1−X /4( V Ti )X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba 1−X Ce 3+ X Ti 4+ 1−X Ti 3+ X O 3 solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.