{111} Twin Formation and Abnormal Grain Growth in Barium Strontium Titanate

Two series of experiments were performed to study the experimental conditions for the formation of {111} twins and related microstructures in barium strontium titanate ((Ba, Sr)TiO 3 ). In the first series, the phase equilibria in the BaTiO 3 –SrTiO 3 –TiO 2 system were determined. XRD and WDS analysis, done in the BaTiO 3 ‐rich region, of 45(Ba,Sr)TiO 3 –10TiO 2 samples annealed at 1250°C for 200 h in air showed that (Ba,Sr)TiO 3 was in equilibrium with Ba 6 Ti 17 O 40 (B 6 T 17 ) and Ba 4 Ti 13 O 30 phases with strontium solubility (Sr/(Ba + Sr)) of ∼0.02 and 0.20, respectively. In the second series the microstructures of samples consisting of a mixture of (Ba,Sr)TiO 3 and 2.0 mol% TiO 2 , were observed after sintering at 1250°C for 100 h in air. {111} twins formed only in the samples with faceted B 6 T 17 second phase particles, similar to the case of BaTiO 3 . In these samples, abnormal grain growth occurred in the presence of the {111} twins. In contrast, no {111} twins formed and no abnormal grain growth occurred in the samples containing second phase particles other than B 6 T 17 . With an increased substitution of strontium for barium, the aspect ratio of abnormal grains containing {111} twin lamellae was reduced. This result was attributed to a reduction in the relative stability of the {111} planes with the strontium substitution.