Synthesis of Ba2TiOSi2O7 and Ba2TiOSi1.8Ge0.2O7 ferroelectric ceramics and the structure determination by Rietveld analysis

Polycrystalline samples of pure fresnoite compounds of formula Ba2TiOSi2O7 and germanium (Ge4+) doped Ba2TiOSi1.8Ge0.2O7 were prepared by a standard solid state reaction technique using high purity oxides and carbonates. Pure fresnoite was sintered at 1300 C while the Ge4+-substituted compound was sintered into pellet form at 1180 C. The formation of the single phase compound was confirmed by XRD and the structural parameters were refined by Rietveld analysis. Good agreement between observed and calculated XRD patterns was obtained from the Rietveld refinement using non-centrosymmetric space group P4bm. The bond distances along with bond angles between atoms for both the compounds and the position of the atoms in the unit cell were calculated and these supported the structural results. The grain size of both the compounds was investigated by SEM. The results are discussed in detail.