Octahedral Distortion and Displacement-Type Ferroelectricity with Switchable Photovoltaic Effect in a 3d³-Electron Perovskite System

Because of the half-filled t(2g)-electron configuration, the BO6 octahedral distortion in a 3d(3) perovskite system is usually very limited. In this Letter, a perovskitelike oxide Hg0.75Pb0.25MnO3 (HPMO) with a 3d(3) Mn4+ state was synthesized by using high pressure and high temperature methods. This compound exhibits an unusually large octahedral distortion enhanced by approximately 2 orders of magnitude compared with that observed in other 3d(3) perovskite systems like RCr3+O3 (R = rare earth). Essentially different from centrosymmetric HgMnO3 and PbMnO3, the A-site doped HPMO presents a polar crystal structure with the space group Ama2 and a substantial spontaneous electric polarization (26.5 mu C/cm(2) in theory) arising from the off-center displacements of A- and B-site ions. More interestingly, a prominent net photocurrent and switchable photovoltaic effect with a sustainable photoresponse were observed in the current polycrystalline HPMO. This Letter provides an exceptional d(3) material system which shows unusually large octahedral distortion and displacement-type ferroelectricity violating the "d(0)-ness" rule.