Formation of Morphotropic Phase Boundary and Electrical Properties of (Bi_1/2Na_1/2)TiO₃–Ba(Al_1/2Nb_1/2)O₃ Solid Solution Ceramics

The phase relations and electrical properties of (1-x)(Bi_1/2Na_1/2)TiO₃–xBa(Al_1/2Nb_1/2)O₃ (abbreviated as BNT–BAN100x) ceramics were investigated in detail. The morphotropic phase boundary (MPB) between the rhombohedral ferroelectric and pseudocubic (tetragonal) relaxor phases of BNT–BAN100x was determined at approximately x=0.055. A maximum piezoelectric constant d₃₃ of 133 pC/N was obtained at x=0.05 and a normalized strain d₃₃^* of 533 pm/V was obtained at x=0.055. This study revealed that the double-like hysteresis loops and large strain observed near the MPB composition are attributed to the 71 and 109° domain switchings and the switching back attributed to the pseudocubic ↔ rhombohedral phase transition. This study also showed the relationship between MPB position and the tolerance factor of the end member ABO₃ for (1-x)BNT–xABO₃ solid solution systems. This indicates that the approximate MPB composition of BNT-based solid solutions can be predicted from the tolerance factors of their end members.