We have investigated the crystal structure of (1 % x)(Bi 1/2 Na 1/2 )TiO 3 -xBa(Mg 1/3 Nb 2/3 )O 3 (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%BaTiO 3 . The P4bm structure exhibits antiparallel displacements of A-and B-site cations, which results in a small spontaneous polarization (P s ) of 13.3 µC/cm 2 (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 P s to other ferroelectric phases with a large P s .

Single crystals of (Bi 1/2 Na 1/2 )TiO 3 Ba(Mg 1/3 Nb 2/3 )O 3 [(1 ¹ x)BNTxBMN] with x = 4% were grown by the flux method (Po 2 = 0.02 MPa) and the high-Po 2 top-seeded solution growth method (Po 2 = 0.9 MPa) and their crystal structures and properties are investigated along the pseudocubic [001] direction. The crystal grown at a higher Po 2 of 0.9 MPa exhibits a well saturated polarization hysteresis, showing that the rhombohedral phase with x = 4% has a spontaneous polarization (P s ) of 48.5¯C/cm 2 (P s parallel to the pseudocubic [111] direction). The superior properties obtained for the crystal (Po 2 = 0.9 MPa) are discussed in terms of domain clamping and depolarization associated with oxygen vacancies.

We investigate the structural variation in the ferrielectric P4bm phase of (1−x)(Bi1/2Na1/2)TiO3–xBa(Mg1/3Nb2/3)O3 (BNT–BMN) by using high-resolution neutron powder diffraction (NPD) analysis. The NPD study on single-phase BNT–BMN powders obtained by a two-step calcination process reveals that a boundary between rhombohedral R3c and tetragonal P4bm phases exists at x = 4%. The Rietveld analysis reveals that the P4bm phase (x = 5%–10%) exhibits an isotropic expansion of the crystal lattice as well as a decrease in rotation angle of the oxygen octahedra when the BMN composition (x) increases. The compositional-driven variation in the P4bm structure strongly suggests that the polarization and octahedral rotation behaviors associated with phase transition, which is called polarization twist, has a crucial role in the enhancement of polarization properties of BNT–BMN.