Structural study of a sol-gel derived pyrochlore Bi2Ti2O7 using a Rietveld analysis method based on neutron scattering studies

The crystal structure of the sol-gel derived pyrochlore Bi2Ti2O7 has been refined by a Rietveld analysis method using both neutron scattering and x-ray diffraction data. The sample contains a majority Bi2Ti2O7 phase and minor Bi4Ti3O12, Bi12TiO20, and TiO2 phases. A total goodness of fit from neutron and x-ray scatterings were chi(2)=2.6, R-p=6.5%, and R-w(p)=8.6%, which suggest that the refinement is reasonable. The structure of the sol-gel derived pyrochlore Bi2Ti2O7 has been identified as a cubic Fd (3) over barm with a lattice constant of 10.3735 (3) angstrom and the calculated chemical composition of Bi1.896Ti2O6.884. Furthermore, the measured electrical properties of the sol-gel Bi2Ti2O7 thin film exhibit a ferroelectricity evident from the measured electric field dependent polarization. The observed ferroelectricity of the Bi2Ti2O7 thin film is attributed mainly by Bi atoms occupying 96g site in the unit cell with probability of 0.158 based on the refinement result. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3056166]