Two kinds of ternary KNN-based lead-free piezoceramics: (0.985-x)K0.5Na0.5NbO3-0.015Bi(0.5)Na(0.5)TiO(3)-xBiScO(3) and (0.985-y)K0.5Na0.5NbO3-0.015Bi(0.5)Na(0.5)TiO(3)-yBiFeO(3) have been prepared by a conventional solid-state sintering. For these KNN-based ceramics, the increasing doping of BiScO3 or BiFeO3 changed the phase structure from orthorhombic symmetry to tetragonal symmetry and then to pseudocubic symmetry, while a typical bimodal grain size distribution was observed in their rectangular grains at x = 0-0.015 or y = 0.06-0.012. With increasing x or y, TO-T gradually decreases to room temperature, and an orthorhombic-tetragonal (O-T) morphotropic phase boundary was formed at 0.009 <= x <= 0.015 or 0.009 <= y <= 0.012. Around the phase boundary, both a good piezoelectric activity and a high Curie temperature were obtained, such as d(33)-320pC/N, k(p)-0.45, T-C = 327 degrees C at x = 0.015, and d(33)-304pC/N, k(p)-0.42;T-C = 350 degrees C at y = 0.012. In addition, the test for the piezoelectric constant following the annealing temperature indicate that these two compositions also have a good thermal stability. (C) 2017 Elsevier Ltd. All rights reserved.