Pseudocubic-based polymorphic phase boundary structures and their effect on the piezoelectric properties of (Li,Na,K)(Nb,Sb)O3-SrZrO3 lead-free ceramics

Abstract

CuO-added 0.96(LixNa0.5-xK0.5)(Nb1-ySby)O3-0.04SrZrO3 ceramics were sintered at 1020 °C for 6 h. Various crystal structures were synthesized in these specimens by controlling the Li2CO3 (x) and Sb2O5 (y) contents: pseudocubic, orthorhombic-pseudocubic polymorphic phase boundary (PPB), tetragonal-pseudocubic PPB, orthorhombic-tetragonal-pseudocubic PPB, and orthorhombic-tetragonal PPB structures. The pseudocubic structure developed in these specimens was similar to the R3m rhombohedral structure instead of the Pm3m cubic structure because the specimens with a pure pseudocubic structure showed good ferroelectric and piezoelectric properties. The piezoelectric properties of the specimens were influenced by their crystal structures. The specimen with the tetragonal-pseudocubic PPB structure showed the best piezoelectric properties because this structure was similar to the tetragonal-rhombohedral morphotropic phase boundary structure developed in Pb(Zr1-xTix)O3-based ceramics. In particular, the specimen with the tetragonal-pseudocubic PPB structure corresponding to x = 0.05 and y = 0.065 showed the largest d33 and kp values of 431 pC/N and 0.43, respectively.