Polymorphic phase transition and excellent piezoelectric performance of (K0.55Na0.45) 0.965 Li0.035Nb 0.80Ta0.20O3 lead-free ceramics

Abstract

A lead-free ceramic with the composition (K0.55Na 0.45) 0.965 Li0.035Nb0.80Ta 0.20O3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d33 =262 pC/N, k p =0.53, k33 =0.63, and k31 =0.31 with ε′ =1290 and tan δ=0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 °C, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between -40 and 85 °C. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to -150 °C and up to about 300 °C. 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. © 2009 American Institute of Physics.