Polymorphic phase transition and enhanced piezoelectric properties of LiTaO3-modified (Na0.52K0.48) (Nb0.93Sb0.07)O3 lead-free ceramics

Lead-free (Na0.52K0.48-x)(Nb0.93-x Sb-0.07)O-3-xLiTaO(3) (NKNS7-xLT) solid solution piezoelectric ceramics were investigated in terms of their phase transition behaviour and various electrical properties. The polymorphic phase transition of NKNS7 compositions with an orthorhombic structure was shifted downwards with the addition of a small amount of LT; however, the tetragonal ferroelectric to cubic paraelectric phase transition was moved slightly upwards. The polymorphic phase boundary between the orthorhombic and the tetragonal phases was thus formed near room temperature among the compositions with 0.03 <= x <= 0.0375 where enhanced piezoelectric and electromechanical properties were achieved. The compositions close to the tetragonal side exhibit better piezoelectric properties and temperature stability. The optimum electrical properties of d(33) = 362 pCN(-1), k(p) = 53%, epsilon(T)(33) = 2165, Q(m) = 37 and T-c = 271 degrees C were obtained in the composition with x = 0.0375. The results indicate that the materials studied could be an excellent candidate for replacing the widely used lead-based piezoelectric ceramics.