Phases in the (1 −x)Na_0.5Bi_0.5TiO₃–(x)CaTiO₃ system

Abstract

The structures of (1 −x)Na_0.5Bi_0.5TiO₃–(x)CaTiO₃ at room temperature have been investigated using neutron powder diffraction and dielectric studies. The system exhibits an orthorhombic (Pbnm) structure for x ≥ 0.15 and rhombohedral (R3c) for x ≤ 0.05. For x = 0.10, though the neutron diffraction pattern shows features of the orthorhombic (Pbnm) structure, Rietveld refinement using this structure shows a drastic reduction in the in-phase tilt angle (∼4°) as compared to the corresponding value (∼8°) for a neighbouring composition x = 0.15. The neutron diffraction pattern of x = 0.10 could be fitted equally well using a two-phase model (R3c + Pbnm) with orthorhombic as the minor phase (22%), without the need for a drastic decrease in the in-phase tilt angle. The dielectric studies of x = 0.10 revealed the presence of the polar R3c phase, thereby favouring the phase coexistence model, instead of a single-phase Pbnm structure, for this composition.