Effect of Fe2O3 additive on structural and piezoelectric properties of (Na,K)(Nb,Sb)O3–CaZrO3–(Bi,Ag)ZrO3 lead-free piezoceramics

Abstract

0.96(Na_0.5K_0.5)(Nb_0.93Sb_0.07)O₃–0.01CaZrO₃–0.03(Bi_0.5Ag_0.5)ZrO₃ (NKNS–CZ–BAZ) lead-free piezoceramic was densified at 1125 °C and possessed large grains (∼41 μm). This piezoceramic had an orthorhombic–tetragonal (O–T) structure and exhibited relatively small d₃₃ and k_p values of 350 pC N⁻¹ and 0.38, respectively. A small amount of Fe₂O₃ was added to the NKNS–CZ–BAZ piezoceramic to enhance its piezoelectric properties. The 0.25 mol% Fe₂O₃-added NKNS–CZ–BAZ piezoceramic on sintering at 1090 °C exhibited a dense microstructure consisting of large grains (∼55 μm). This piezoceramic has an ideal rhombohedral–orthorhombic–tetragonal (R–O–T) structure where the proportions of R, O, and T structures are similar to each other. Furthermore, this piezoceramic exhibited very large d₃₃ and k_p values of 680 pC N⁻¹ and 0.47, respectively. Therefore, the Fe₂O₃ additive considerably improved the piezoelectric properties of the NKNS–CZ–BAZ lead-free piezoceramic through the development of an ideal R–O–T structure and a marginal increase in the grain size.