Electrical and structural characterization of (KxNa1−x)NbO3ceramics modified with Li and Ta

Abstract

(KxNa1−x)NbO3ceramics modified with Li+and Ta5+have been produced using the mixed-oxide synthesis method. Synchrotron X-ray diffraction measurements were made on the samples from 12 K to temperatures above their ferroelectric–paraelectric transition points with 10 K measurement steps. Rietveld refinement was used to refine the patterns. Depending on the composition and temperature, rhombohedral phases, orthorhombic phases, tetragonal phases, cubic phases and two-phase mixtures were obtained. Space groupsR3c(161),Amm2 (38),P4mm(99) and Pm{\overline 3}m (221) and their combinations were used to refine the rhombohedral, orthorhombic, tetragonal, cubic and mixed phases, respectively. Li+addition suppressed the formation of the rhombohedral low-temperature phase and increased the Curie temperature. This is attributed to the size difference in ionic radii of theA-site elements, which leads to increased atomic polarizability and increased interaction with theB-site element. Li+and Ta5+co-doping led to a wide temperature range of coexistence between the orthorhombic and tetragonal phases. Electrical characterizations by dielectric and hysteresis measurements were used to compare with the results from the structural studies.