Physical and electric properties of lead-free (Bi_0.5Na_0.5)TiO₃-Ba(Zr_0.04Ti_0.96)O₃ ceramics near the morphotropic phase boundary

Abstract

Extending the investigations on Bi-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (1-x)(Bi_0.5Na_0.5)TiO₃-xBa(Zr_0.04Ti_0.96)O₃ [(1-x)BNT-xBZT] for x < 0.12. High density polycrystalline ceramics were fabricated using conventional solid-state processing methods. These ceramics are then taken for structure and properties measurements. A morphotropic phase boundary (MPB) between hexagonal (H) and tetragonal (T) was found at the composition 0.95BNT-0.05BZT with correspondingly enhanced dielectric and piezoelectric properties. Owing to the phase coexistence at the phase boundary, there exists a different symmetry regions (DSR) near the MPB. The DSR boundary motion increases the dielectric permittivity and piezoelectric coefficients. The planar coupling factor and piezoelectric constant are higher for compositions near the MPB. The effect of sintering time on the properties of 0.95BNT-0.05BZT ceramic was studied. Dielectric and piezoelectric properties have maximum values at the sintering temperature of 1100°C for 5 h. The dielectric constant (K^T₃₃) and electromechanical coupling coefficient (k_p) of 0.95BNT-0.05BZT ceramic were 850 and 34%, respectively. For 0.99(Bi_0.5Na_0.5)TiO₃-0.01Ba(Ti_0.96Zr_0.04)O₃ ceramics, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.14 and 0.51, respectively, at the sintering of 1100°C for 5 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 3.6. Our results show that (Bi_0.5Na_0.5)TiO₃-Ba(Zr_0.04Ti_0.96)O₃ solid solution ceramics are one of the promising lead-free ceramics for high frequency electromechanical transducer applications.