Theoretical predictions of morphotropic phase boundary in (1-x)Na1/2Bi1/2TiO3-xBaTiO3 by first-principle calculations

A morphotropic phase boundary (MPB) in a solid solution of (1-x)Na1/2Bi1/2TiO3-xBaTiO(3) (0a parts per thousand currency signxa parts per thousand currency sign1.0) (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 0.05a parts per thousand currency signxa parts per thousand currency sign0.07. 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 0.05a parts per thousand currency signxa parts per thousand currency sign0.07 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 < x < 0.65.