Evidence for Pb-O covalency in tetragonal PbTiO3 -: art. no. 217601

Accurate charge-density distributions of cubic and tetragonal PbTiO3 and BaTiO3 have been obtained by the MEM(maximum entropy method)/Rietveld analysis using synchrotoron-radiation powder data. The Pb-O bonds in tetragonal PbTiO3 show rather strong cova ncy, while those in ubic PbTiO3 are ionic. This is the clear evidence of the Pb-O hybridization in tetragonal PbTiO3, which has been theoretically predicted as a key factor of much larger ferroelectricity of this substance than that of BaTiO3. Tetragonal PbTi03 forms a layered structure of a two-dimensional covalent-bonding network consisting of the Ti-O-5 pyramid.