Precise charge density analysis of PbTiO3

Precise charge-density distributions of cubic and tetragonal PbTiO3 have been investigated associated with the ferroelectric phase transition at 763K, by means of the MEM/Rietveld analysis using synchrotron radiation X-ray powder-diffraction data. It has been clearly visualized that cubic PbTiO3 consists of the three-dimensional covalent network of TiO6 octahedra and isolated Pb2+ ions, whereas tetragonal PbTiO3 forms a layered structure with the two-dimensional covalent network of TiO5 pyramids, to which Pb atoms are also covalently bonded. These findings on the binding nature of tetragonal PbTiO3 give good agreement with theoretical predictions by the first-principles calculations.