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

摘要

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 ℃ 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°) in textured KNN ceramics. The best electromechanical properties (k_p ≈ 0.58, k_(31) ≈ 0.33, d_(33) ≈ 146 pC/N, T_(o-t) ≈ 183 ℃, T_c ≈ 415 ℃, ε_r = 202, and tan δ = 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 ℃). These results show that high-quality textured KNN can be obtained by TGG and that a reactive matrix is unnecessary.