STRUCTURAL PARAMETERS AND ELECTRON DIFFERENCE DENSITY IN BATIO3

Barium titanate, BaTiO3, M(r) = 233.24, tetragonal, P4mm, a = 3.9998 (8), c = 4.0180 (8) angstrom, v = 64.281 (3) angstrom3, Z = 1, D(x) = 6.024 Mg M-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 18.60 mm -1, F(000) = 102, T = 298 K, R = 0.013, wR = 0.013 for 243 unique reflections. Structural parameters and electron difference densities for BaTiO3 determined from two sets of X-ray diffraction data measured independently with Mo Kalpha radiation are in close agreement. The average cubic structure, the average centrosymmetric tetragonal structure and the correct non-centrosymmetric structure were refined, and the difference density DELTArho was evaluated for each model. In the non-centrosymmetric model the z and U33 parameters are highly correlated, but the least-squares refinements were stable. The O-atom vibrations along the Ti-O bonds are smaller than the Ti amplitudes. The atomic charges reflect the combined effects of electronegativities and the electron depletion due to the close packing of the Ba atoms in the structure. In the centrosymmetric average structures the topography of DELTArho resembles that observed for cubic SrTiO3. For the correct non-centrosymmetric structure the topography of DELTArho near the Ti nucleus has the characteristics required for stability at that position.