Structure Refinement of a Sol-gel Derived Pyrochlore Bi$_{2}$Ti$_{2}$O$_{7}$ Using a Neutron Scatterings

Structure of the sol-gel derived pyrochlore Bi$_{2}$Ti$_{2}$O$_{7}$ has been refined by a Rietveld analysis method using neutron and x-ray scattering data. The structure of Bi2Ti2O7 was assumed as Fd-3m (space group number 227). The calculated lattice constant was 10.3735(3) nm. The sample contains a majority Bi$_{2}$Ti$_{2}$O$_{7}$ phase and minor Bi$_{4}$Ti$_{3}$O$_{12}$, Bi$_{12}$TiO$_{20}$, and TiO$_{2}$ phases. After subtracting the secondary phases effect, the total goodness of fit using both scatterings was conversed to $\chi ^{2}$ = 2.6, Rp = 6.5 {\%}, and wRp = 8.6 {\%}, which suggesting that the refined structure of Bi$_{2}$Ti$_{2}$O$_{7}$ is reasonable. Bi atom occupies 96 g site with probability of 0.158(1), while O occupies 8 a site by 0.884(16). Furthermore, Bi$_{2}$Ti$_{2}$O$_{7}$ thin film has been fabricated by a sol-gel method. After depositing electrodes, electrical properties of the thin film have been measured. Interestingly, a ferroelectric characteristics has been observed; electric field dependent dielectric constant. The refined structure information of Bi$_{2}$Ti$_{2}$O$_{7}$ may explain the observed ferroelectricity of the thin films. Details of the structural and electrical properties of Bi$_{2}$Ti$_{2}$O$_{7}$ will be discussed.