Because of the half-filled $t_{2g}$-electron configuration, the $B{\mathrm{O}}_6$ octahedral distortion in a $3d^3$ perovskite system is usually very limited. In this Letter, a perovskitelike oxide ${\mathrm{Hg}}_{0.75}{\mathrm{Pb}}_{0.25}{\mathrm{MnO}}_3$ (HPMO) with a $3d^3$ ${\mathrm{Mn}}^{4+}$ 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 $R{\mathrm{Cr}}^{3+}{\mathrm{O}}_3$ ($R=\text{rare}$ earth). Essentially different from centrosymmetric ${\mathrm{HgMnO}}_3$ and ${\mathrm{PbMnO}}_3$, the $A$-site doped HPMO presents a polar crystal structure with the space group $Ama2$ and a substantial spontaneous electric polarization ($26.5\mathrm{\mu }\mathrm{C}/{\mathrm{cm}}^2$ 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.

• Received 19 July 2022
• Revised 2 December 2022
• Accepted 14 March 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.146101