Electrical and structural characterization of (KxNa1-x)NbO3 ceramics modified with Li and Ta

(KxNa1-x)NbO3 ceramics 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 groups R3c (161), Amm2 (38), P4mm (99) and Pm anti 3m (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 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. (orig.)