Polymorphic phase transition and excellent piezoelectric performance of (K_(0.55)Na_(0.45))_(0.965)Li_(0.035)Nb_(0.80)Ta_(0.20)O_3 lead-free ceramics

摘要

A lead-free ceramic with the composition (K_(0.55)Na_(0.45))_(0.965)Li_(0.035)Nb_(0.80)Ta_(0.20)O_3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d_(33) = 262 pC/N, k_p=0.53, k_(33)=0.63, and k_(31) = 0.31 with ε' = 1290 and tan δ=0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 ℃, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between -40 and 85 ℃. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to -150 ℃ and up to about 300 ℃. It is suggested that the outstanding piezoelectric performance of this ceramic can be largely ascribed to the phase coexistence in a wide temperature range and the Ta-rich composition.