Ferrielectric phase in the (Bi_1/2Na_1/2)TiO₃–Ba(Mg_1/3Nb_2/3)O₃system

Abstract

We have investigated the crystal structure of (1 − x)(Bi1/2Na1/2)TiO3–xBa(Mg1/3Nb2/3)O3 (BNT–BMN) by high-resolution neutron powder diffraction (NPD) analysis. Our NPD study combined with polarization hysteresis measurements for ceramics reveals that a boundary between rhombohedral R3c and tetragonal P4bm phases exists at x = 4–5%. The Rietveld analysis of the NPD data shows that the crystal structure with x = 10% has a single-phase tetragonal structure in space group P4bm, as has been reported for BNT–7%BaTiO3. The P4bm structure exhibits antiparallel displacements of A- and B-site cations, which results in a small spontaneous polarization (Ps) of 13.3 µC/cm2 (estimated from the refined structural parameters). The results obtained for BNT–10%BMN ceramics strongly suggest ferrielectric features; the application of electric fields induces a transition from the P4bm phase with a small Ps to other ferroelectric phases with a large Ps.