Polarization properties and crystal structures of ferroelectric (Ba,Ca)TiO3 single crystals

We have investigated the spontaneous polarization (P s ) of Ba 1-x Ca x TiO 3 (BCT) by polarization hysteresis measurements using single crystals and by density functional theory (DFT) calculations. Single crystals of BCT (x = 0.07) were grown by a top-seeded solution growth (TSSG) method. The polarization measurements show that the crystals (x = 0.07) have a P s of 26.0 μC/cm 2 , which is slightly small compared with BaTiO 3 (27.3 μC/cm 2 ). Our DFT calculations based on a supercell approach show that Ca atoms are markedly displaced cooperatively with the adjacent Ti atoms along the P s direction. It is suggested that the CaTiO 3 -like octahedral rotation is constructed in the BCT supercell around the Ca atoms, which is the origin of the smaller P s observed for the BCT crystals.