(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 12K to temperatures above their ferroelectric-paraelectric transition points with 10K measurement steps. Rietveld refinement using FULLPROF suite was used to refine the patterns. Depending on the composition and temperature, rhomhohedral phases, orthorhombic phases, tetragonal phases, cubic phases and two-phase mixtures were obtained. R3c (161), Amm2 (38), P4mm (99), (221) space groups and their combinations were used to refine the rhombohedral, orthorhombic, tetragonal, cubic and the mixed phases respectively. Li+ addition suppressed the formation of the rhombohedral low temperature phase and increased the Curie temperature. This is attributed to 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 phase coexistence between the orthorhombic and tetragonal phase. Electrical characterizations by dielectric and hysteresis measurements were used to compare with the results from the structural studies.