Composition Dependent Dielectric Anomaly in Na_1−xK_xNbO₃, at x = 0.475

Abstract

Sodium-potassium niobate (Na1−xKxNbO3) pellet samples, with x = 0.40, 0.47, 0.475, 0.48 and 0.50, were prepared by solid state reaction method. With varying composition (x), X-ray diffraction patterns show a break in the peak shifting tendency, at x = 0.475. Lattice parameters calculated from X-ray diffraction patterns show a slope change anomaly, in the a/b vs. x plot, from positive to negative, at x = 0.475. Dielectric constant, loss tangent and dielectric conductivity were found minimum for the composition with x = 0.475, among the prepared compositions, at all measured frequencies and temperatures. The observed results show a strong compositional dependence of dielectric properties, in this system. Observed minimum values of dielectric parameters may be associated with increased Na site vacancies and structural anomaly- a morphotropic type phase transition, at the composition with x = 0.475.