| Lead-free piezoelectric ceramics with the nominal composition of [(K0.5Na0.5)0.94Li0.06]NbO3+xmol%CuO [KNLN+ xmol%CuO] had been synthesized by conventional solid-state sintering. Effects of the addition of CuO on the phase structure, micro-morphology evolution and electric properties of the ceramics were investigated. The ceramics synthesized at 1000¨C1060¡æ showed a phase transition from orthorhombic to tetragonal symmetry, which is analogous to the morphtropic phase boundary (MPB). Because of this polymorphic phase transition, high piezoelectric coefficient d33¡«206pC/N and electromechanical coupling factor kp ¡«31% were obtained in the pure KNLN ceramic sintered at 1060¡æ, however, the mechanical quality factor Qm, a key parameter for frequency devices, was relatively low. In order to improve the resonance characteristics, CuO had been doped in KNLN ceramics. Our results showed that the doping of CuO was effective in promoting the densification of the ceramics and hardening of piezoelectric properties. |