Crystal Structural Analyses of Ferrielectric Tetragonal (Bi1/2Na1/2)TiO3--7%BaTiO3 Powders and Single Crystals

We have investigated the crystal structure of (Bi 1/2 Na 1/2 )TiO 3 --7%BaTiO 3 (BNT--7%BT) by high-resolution neutron powder diffraction (NPD) and high-energy synchrotron radiation X-ray diffraction (SR-XRD) analyses. The NPD study revealed that the BNT--7%BT crystals have a single-phase tetragonal structure with $P4bm$ symmetry. The crystal structure refined by the Rietveld method was found to be similar to the ferrielectric $P4bm$ phase reported for BNT at a high temperature of 673 K. The SR-XRD analyses for single crystals of BNT--7%BT demonstrated that the $P4bm$ phase remains as a stable phase in the crystals even after a high electric field is applied for poling, which is different from the structural analysis of ceramics by Ma et al. [Phys. Rev. Lett. 109 (2012) 107602].