Lead-free piezoelectric ceramics based on perovskite structures

The piezoelectric properties of a solid solution based on three components of bismuth sodium titanate (Bi_1/2Na_1/2)TiO₃ (BNT), bismuth potassium titanate, (Bi_1/2K_1/2)TiO₃ (BKT), and barium titanate, BaTiO₃ (BT), that is x(Bi_1/2Na_1/2)TiO₃−y(Bi_1/2K_1/2)TiO₃−zBaTiO₃, [\( x + y + z = 1 \), abbreviated as BNBKy:z(x)] and potassium niobate, KNbO₃ (KN) based ceramics, that is KN+MnCO₃ x wt.%, [abbreviated as KN−Mn x], were studied as a lead-free piezoelectric material. In the case of BNBK2:1 system, high piezoelectric properties were obtained near the MPB composition, and the highest electromechanical coupling factor, k ₃₃ and piezoelectric constant, d ₃₃, were 0.58 for BNBK2:1(0.89) and 181 pC/N for BNBK2:1(0.88). Nevertheless, the depolarization temperature, T _d , shifts to lower temperature around the MPB compositions, and the T _d ’s of BNBK2:1(0.88–0.90) are only about 100 °C. On the tetragonal side, the T _d shifts to higher temperature with increasing the lattice anisotropy, c/a. As T _d higher than 200 °C was obtained in the range of x < 0.78, with a k ₃₃ and d ₃₃ for BNBK2:1(0.78) being 0.45 and 128 pC/N, respectively. In the case of Mn doped KN ceramics, dense and non deliquescence KN ceramic were successfully obtained via ordinary firing technique in air by optimizing the fabrication process. Mn doping for KN ceramics was effective to obtain full poling state easily under poling conditions of high temperature and high electric field. As a result, we obtained the excellent piezoelectric properties of k ₃₃ = 0.507 for KN−Mn0.2.