Crystal structure of the high-temperature paraelectric phase in barium titanate BaTi2O5

Crystal structure of a ferroelectric barium titanate BaTi2O5 was investigated by the Rietveld analysis of neutron powder diffraction data measured at 706°C. The crystal structure of BaTi2O5 at 706°C was refined assuming the centrosymmetric monoclinic A2∕m space group. The crystal structures of the high-temperature A2∕m and low-temperature A2 phases are similar. The displacement of atoms along the b axis is accompanied by the paraelectric A2∕m to ferroelectric A2 phase transformation. The A2∕m-A2 transition is not reconstructive but displacive.