Microstructure, phase transition, and electrical properties of (K0.5Na0.5)1-xLix(Nb1-yTay)O3 lead-free piezoelectric ceramics

Lead-free ceramics (K0.5Na0.5)(1-x)Li-x(Nb1-yTay)O-3 have been prepared by an ordinary sintering technique. Our results reveal that Li+ and Ta5+ diffuse into the K0.5Na0.5NbO3 lattices to form a solid solution with a perovskite structure. The substitution of Li+ induces an increase in the Curie temperature (T-C) and a decrease in the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (TO-T). On the other hand, both TC and TO-T decrease after the substitution of Ta5+. A coexistence of the orthorhombic and tetragonal phases is formed at 0.03 < x < 0.06 and 0.10 < y < 0.25 near room temperature, leading to significant enhancements of the piezoelectric properties. For the ceramic with x=0.04 and y=0.225, the piezoelectric properties become optimum, giving a piezoelectric coefficient d(33)=208 pC/N, electromechanical coupling factors k(p)=48% and 2 k,=49%, remanent polarization P-r=14.2 /mu C/cm(2), coercive field E-c=1.21 kV/mm, and Curie temperature T-C= 320 degrees C. (c) 2007 American Institute of Physics.