A-Site Ordered Double Perovskite CaMnTiO as a Multifunctional Piezoelectric and Ferroelectric-Photovoltaic Material.

The double perovskite CaMnTiO, is a rare A-site ordered perovskite oxide that exhibits a sizable ferroelectric polarization and relatively high Curie temperature. Using first-principles calculations combined with detailed symmetry analyses, we identify the origin of the ferroelectricity in CaMnTiO. We further explore the material properties of CaMnTiO, including its ferroelectric polarization, dielectric and piezoelectric responses, magnetic order, electronic structure, and optical absorption coefficient. It is found that CaMnTiO exhibits room-temperature-stable ferroelectricity and moderate piezoelectric responses. Moreover, CaMnTiO is predicted to have a semiconducting energy band gap similar to that of BiFeO, and its band gap can further be tuned via distortions of the planar Mn-O bond lengths. CaMnTiO exemplifies a new class of single-phase semiconducting ferroelectric perovskites for potential applications in ferroelectric photovoltaic solar cells.