Structural, Dielectric, and Piezoelectric Properties of Mn-Doped BaTiO3--Bi(Mg1/2Ti1/2)O3--BiFeO3 Ceramics

Mn-doped ($0.9-x$)BaTiO 3 --0.1Bi(Mg 1/2 Ti 1/2 )O 3 --$x$BiFeO 3 ($x = 0.6$, 0.7, and 0.8) ceramics were studied as candidate lead-free piezoelectric materials. The crystal structures were a pseudo-cubic perovskite at $x = 0.6$, a rhombohedral perovskite at $x = 0.8$, and a mixture of the pseudo-cubic and rhombohedral perovskite at $x = 0.7$. The Curie temperature was found to be 470 °C at $x = 0.6$ and more than 600 °C at $x = 0.7$ and 0.8. A strong pinning of domain walls was observed for high-field responses at $x = 0.7$ and 0.8, which was relaxed by high-temperature annealing and subsequent quenching. Piezoelectric properties increased with decreasing $x$, and the small-field piezoelectric constants $d_{33}$ and $d_{31}$ were 94 and 31 pC/N at $x = 0.6$, respectively.