Lead-free (K0.5Na0.5)(Nb1-xTax)O-3 ceramics with x = 0.00-0.30 were prepared by the solid-state reaction technique. The effects of Ta on microstructure, crystallographic structure, phase transition and piezoelectric properties have been investigated. It has been shown that the substitution of Ta decreases Curie temperature T-c and orthorhombic-tetragonal phase transition temperature TO-T, while increasing the rhombohedral-orthorhombic phase transition temperature TR-O. In addition, piezoelectric activity is enhanced with the increase of Ta content. The ceramics with x = 0.30 have the high value of piezoelectric coefficient d(33) = 205 pC/N. Moreover, k(p) shows little temperature dependence between -75 degrees C and 75 degrees C, and d(33) exhibits very good thermal stability over the range from -196 degrees C to 75 degrees C in the aging test. (C) 2008 Elsevier Ltd. All rights reserved.