Theoretical predictions of morphotropic phase boundary in (1-x)Na _1/2Bi_1/2TiO₃-xBaTiO₃ by first-principle calculations

A morphotropic phase boundary (MPB) in a solid solution of (1 - x) Na _1/2Bi_1/2TiO₃-xBaTiO₃ (0 ≤ x ≤ 1.0) (NBT-BT) is directly demonstrated by first-principle calculations. The results show that in the NBT-BT system, a structural transition from rhombohedral to tetragonal occurs when x is changed from 0.06 to 0.12, and the MPB appears at compositions of around 0.05 ≤ x ≤ 0.07. It can be verified by the stronger hybridization orbital of p-d based on the analysis of the partial density of states (PDOS) in the Ti-O atoms. The theoretical predictions agree well with experimental observations which indicate that the best ferroelectric properties can be attained in the vicinity of around 0.05 ≤ x ≤ 0.07 in the MPB of the NBT-BT system. Another tetragonal-cubic phase transition which needs further experimental verification is also found from the system with compositions of 0.475