Electrical and structural characterization of (K x Na 1− x )NbO 3 ceramics modified with Li and Ta

(K x Na 1− x )NbO 3 ceramics modified with Li + and Ta 5+ 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 groups R 3 c (161), Amm 2 (38), P 4 mm (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 the A -site elements, which leads to increased atomic polarizability and increased interaction with the B -site element. Li + and Ta 5+ 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.