Ferroelectric ceramics of 2(Pb,Sr)Nb₂O₆:(K,Na)NbO₃ tungsten bronze morphotropic phase boundary system

Abstract

Systematic study of the chemistry-structure-property relation in α(Pb_1-xSr_x)Nb₂O₆:β(K_1-yNa_yNbO₃ oxide system has been carried out for α:β = 2:l and x = y. The experimental work is focused around compositions near the potential morphotropic phase boundary (MPB) that separates the ferroelectric orthorhombic (m2m) and ferroelectric pseudo-tetragonal phase (mm2). Ceramics of various compositions are prepared by solid state route and characterized for crystallographic phases and phase transitions using X-ray diffraction and thermal expansion measurements. Dielectric properties of these compositions as a function of temperature and frequency are studied. XRD analysis indicates the coexistence of pseudo-tetragonal and orthorhombic phases near x = 0.295. The dielectric permittivity reaches a maximum and phase transition temperature reaches a minimum near this composition.