Morphotropic phase-boundary-like characteristic in a lead-free and non-ferroelectric (1-x)NaNbO₃-xCaTiO₃ system

Abstract

We report here an anomalous peak in the composition dependence of the dielectric permittivity of non-ferroelectric (1-x)NaNbO₃-xCaTiO₃ ceramics for the composition range 0.10<x<0.20. This is reminiscent of a similar phenomenon in the ferroelectric morphotropic phase boundary ceramics. Rietveld analysis of the powder x-ray diffraction data for various compositions reveals that this peak is linked with a change of crystal structure from one orthorhombic phase in the Pbma space group for 0 x 0.10 to another orthorhombic phase in the Pbnm space group for x 0.20 through an intermediate long period modulated orthorhombic phase whose lattice parameter is ~14 times the lattice parameter of the Pbnm phase of CaTiO₃ in the [010] direction (q~[0,1/14,0]).