Phase structure and electrical properties of lead free Na 0·5 Bi 0·5 TiO 3 –CaTiO 3 ceramics

Abstract

(1−x)Na_0·5Bi_0·5TiO_3−xCaTiO₃ ceramics with x = 0–0·2 were prepared by solid state sintering method. Structural and morphology studies carried out by X-ray diffraction and scanning electron microscopy indicate the change in crystal structure from rhombohedral to orthorhombic symmetry (R3C to Pnma). The morphotropic phase boundary of this system was found to lie around x = 0·08–0·14, where the orthorhombic and rhombohedral symmetries coexist. The orthorhombic phase is stabilised for x>0·14, indicating that the rhombohedral phase of Na_0·5Bi_0·5TiO₃ is susceptible to orthorhombic distortion brought about by Ca substitution. Calcium substitution in Na_0·5Bi_0·5TiO₃ caused an obvious decrease in peak temperature and a decrease in relative permittivity. The compositional variation of the fundamental dielectric behaviour is discussed in relation to the crystal chemistry of the system. The highest piezoelectric constant d₃₃ of 85 pC N⁻¹ is achieved for x = 0·1, with the coercive field of 18 kV cm⁻¹ and the dielectric maximum temperature of 148°C.