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Double-Exchange Effect in Two-Dimensional MnO2 Nanomaterials
J. Am. Chem. Soc. 139(14):5242-5248b Apr 2017

Peng, Xu; Guo, Yuqiao; Yin, Qin; Wu, Junchi; Zhao, Jiyin; Wang, Chengming; Tao, Shi; Chu, Wangsheng; Wu, Changzheng; Xie, Yi

Electronic state transitions, especially metal–insulator transitions (MIT), offer physical properties that are useful in intriguing energy applications and smart devices. But to-date, very few simple metal oxides have been shown to undergo electronic state transitions near room temperature. Herein, we demonstrate experimentally that chemical induction of double-exchange in two-dimensional (2D) nanomaterials brings about a MIT near room temperature. In this case, valence-state regulation of a 2D MnO2 nanosheet induces a Mn(III)–O–Mn(IV) structure with the double-exchange effect, successfully triggering a near-room-temperature electronic transition with an ultrahigh negative magneto-resistance (MR). Double-exchange in 2D MnO2nanomaterials exhibits an ultrahigh MR value of up to −11.3% (0.1 T) at 287 K, representing the highest reported negative MR values in 2D nanomaterials approaching room temperature. Also, the MnO2 nanosheet displays an infrared response of 7.1% transmittance change on going from 270 to 290 K. We anticipate that dimensional confinement of double-exchange structure promises novel magneto-transport properties and sensitive responses for smart devices.

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