Lead-free piezoelectric ceramics derived from the K0.5Na0.5NbO3-AgNbO3 solid solution system

A lead-free solid solution between potassium sodium niobate and silver niobate, (1-x)wK(0.5)Na(0.5)NbO(3)-xAgNbO(3) (KNN-AN, with x=0-0.36), has been prepared in the form of ceramics by solid state reaction under O-2 atmosphere. The crystal chemical study shows that Ag+ ion diffuses into the KNN lattices to form a solid solution of perovskite structure with x up to 0.30. The substitution of Ag+ ion for (K0.5Na0.5)(+) ion results in linear decreases in the ferroelectric Curie temperature (T-C), from 420 degrees C in KNN down to 325 degrees C in 0.70KNN-0.30AN, and in the tetragonal to orthorhombic phase transition temperature (TT-O), from 190 down to 150 degrees C. The relative density of the KNN-AN ceramics reaches 94%. The optimum piezoelectric properties are found in the ceramics of 0.82KNN-0.18AN, with a piezocoefficient d(33)=186 pC/N, an electromechanical coupling factor k(p)=42.5%, and a T-C=355 degrees C. For the ceramics with x=0.24, the remanent polarization reaches a maximum value of P-r=20 mu C/cm(2), with a reduced coercive field E-c = 6.4 kV/cm and a T-C=340 degrees C. It is shown that the (1-x)KNN-xAN ceramics exhibit piezoelectric properties which are comparable or superior to the hot-pressed KNN ceramics and other KNN-based systems. In particular, the piezoelectric properties exhibit very a good thermal stability up to high temperature, which is a significant improvement from other KNN-based piezoceramics. (C) 2008 American Institute of Physics.