Octahedral Distortion and Displacement-Type Ferroelectricity with Switchable Photovoltaic Effect in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>3</mml:mn><mml:msup><mml:mrow><mml:mi>d</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>-Electron Perovskite System
Bowen Zhou, Jie Zhang, X. B. Ye, G. X. Liu, Xiulai Xu, Junjian Wang, Z. H. Liu, Lin Zhou, Zhiyu Liao, Hanmin Yao, Shuai Xu, Jiangjian Shi, Xudong Shen, Xiaohui Yu, Zhiwei Hu, H. J. Lin, Chien‐Te Chen, X. G. Qiu, Cheng Dong, Jinxing Zhang, Richeng Yu, Pu Yu, Kuijuan Jin, Qingbo Meng, Youwen Long
Abstract
Because of the half-filled t_{2g}-electron configuration, the BO_{6} octahedral distortion in a 3d^{3} perovskite system is usually very limited. In this Letter, a perovskitelike oxide Hg_{0.75}Pb_{0.25}MnO_{3} (HPMO) with a 3d^{3} 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 RCr^{3+}O_{3} (R=rare earth). Essentially different from centrosymmetric HgMnO_{3} and 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 μC/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.