Microstructure development and piezoelectric properties of highly textured CuO-doped KNN by templated grain growth

This paper demonstrates the production of < 001 >-oriented CuO-doped (K(0.476)Na(0.524))NbO(3) (KNN) piezoelectric ceramics with a polymorphic phase transition (PPT) temperature greater than 180 degrees C by templated grain growth (TGG) using high aspect ratio NaNbO(3) template particles. A novel (to the KNN system) two-step sintering and annealing process combined with CuO doping is demonstrated to improve density and maximize texture quality (F(001) = 99% and rocking curve FWHM = 6.9 degrees) in textured KNN ceramics. The best electromechanical properties (k(p) approximate to 0.58, k(31) approximate to 0.33, d(33) approximate to 146 pC/N, T(o-t) approximate to 183 degrees C, T(c) approximate to 415 degrees C, epsilon(r) = 202, and tan delta = 0.016) are achieved in 1 mol% CuO-doped KNN with F(001) = 99% and a relative density of 96.3%. The values of d(33), k(p), and k(31) are 70-90% higher than randomly oriented ceramics and are obtained without a significant reduction in the PPT temperature, resulting in stable piezoelectric performance over a wide temperature range (-50 to 180 degrees C). These results show that high-quality textured KNN can be obtained by TGG and that a reactive matrix is unnecessary.