Crystal structure refinement of co-doped Ba0.88Ca0.12Ti0.975Sn0.025O3 ceramic

Abstract

Ba/Ca-doped barium titanate has been prepared by solid state reaction to produce Ba0.88Ca0.12-Ti0.975Sn0.025O3(BCST) ceramics. Five samples were irradiated using neutron fluence of 8.1 106, 9.72 107, 8.75 108, 6.99 109 and 1.4 1010 n/cm2 (BCST-06 to -10). The structure and phase compositions of the control (BCST) and irradiated samples were determined by X-ray diffraction and indicate the presence of a majorly single phase tetragonal barium titanate (S.G.P4mm) with a minor phase CaTiO3 (orthorhombic). However, Rietveld refinement using GSAS II suite of programs indicates a tetragonality ratio (c/a ¼ 0.996) which is pseudocubic with a reduction in volume of 0.03% in the control compared to pristine BT. The irradiated samples exhibited changes in tetragonality (maximum of 0.82%) and variation in volume (0.58%, maximum) over the range of fluence investigated. A complete vacancy was observed in the Ca site of BCST10 but not in the oxygen sites while the occupancies of other metal sites varied. The substitution of Sn is expected to lead to a lower transition temperature and an increase in dielectric constant near the transition temperature of the control. While the changes in volume, tetragonality and occupancy of the irradiated samples are expected to affect their electromechanical properties due to changes in the Ti octahedra which would lead to a slight degradation in device performance.