Phase Composition of Reduced and Reoxidized Barium Titanate

Reducing high‐purity BaTiO 3 in hydrogen for 1 h at 1275°C leads to an oxygen deficiency x = 0.0036 in BaTiO 3–x with maintenance of the tetragonal/cubic perovskite‐type structure. Reduction at 1325° C leads to x = 0.0073 and brings about transformation to the hexagonal modification. Up to 1500°C ( x = 0.0233) no further phase change occurs. Annealing the oxygen‐deficient hexagonal phase in oxygen at 850° C for 2 h produces stoichiometric samples which are still hexagonal, whereas the tetragonal/cubic structure is restored by heating for 1 h at 1350°C. The unit cell found for the hexagonal phase is somewhat smaller than previously reported.