High-Temperature Monoclinic Cc Phase with Reduced c/a Ratio in Bi-based Perovskite Compound Bi₂ZnTi_1-xMn_xO₆

Monoclinic phases with Cm, Pm, and Cc space groups are indispensable to understand the high performance of electromechanical properties at the morphotropic phase boundary (MPB) of lead-based perovskite oxides Pb(Zr_xTi_1-x)O₃ (PZT), [Pb(Mg_1/3Nb_2/3)O₃]_1-x-(PbTiO₃)_x (PMN-PT), and [Pb(Zn_1/3Nb_2/3)O₃]_1-x-(PbTiO₃)_x (PZN-PT). Here, a nearly single monoclinic phase with space group Cc was observed in the Bi-based lead-free perovskite compound Bi₂ZnTi_1-xMn_xO₆ at x = 0.4. This phase was the same as the low-Temperature phase of the MPB composition of PZT but existed at a much higher temperature. Despite the reduced pseudo c/a ratio of 1.065, which is the same as that of PbTiO₃ at room temperature, ionic model calculation based on the Rietveld refinement data indicated the polarization of Bi₂ZnTi_0.6Mn_0.4O₆ is 95.8 μC/cm². The tilting and significant anisotropic distortion of the octahedron were found to cause the c/a ratio to reduce. Accordingly, the effective piezoelectric constant d₃₃ of Bi₂ZnTi_0.6Mn_0.4O₆ thin film was found to be 12 pm/V.