Cooperative Characterization of <i>In Situ</i> TEM and Cantilever-TGA to Optimize Calcination Conditions of MnO<sub>2</sub> Nanowire Precursors.

Zhou, Yufan; Li, Ming; Zhang, Tao; Chen, Ying; Li, Xinyu; Jia, Hao; Xu, Pengcheng; Li, Xinxin · Nano Lett · 2023

basic_science · Level V

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Abstract

Calcination plays a vital role during material preparation. However, the calcination conditions have often been determined empirically or have been based on trial and error. Herein we present a cooperative characterization approach to optimize calcination conditions by gas-cell <i>in situ</i> TEM in collaboration with microcantilever-based thermogravimetric analysis (cantilever-TGA) techniques. The morphological evolution of precursors under atmospheric conditions is observed with <i>in situ</i> TEM, and the right calcination temperature is provided by cantilever-TGA. The proposed approach successfully optimizes the calcination conditions of fragile MnO<sub>2</sub> nanowire precursors with multiple valence products. The cantilever-TGA shows that a calcination temperature above 560 °C is required to transform the MnO<sub>2</sub> precursor to Mn<sub>3</sub>O<sub>4</sub> under an N<sub>2</sub> atmosphere, but the <i>in situ</i> TEM indicates that the nanowire structure is destroyed within only 30 min under calcination conditions. Our method further suggests that heating the precursor at 400 °C using an H<sub>2</sub>-containing atmosphere can produce Mn<sub>3</sub>O<sub>4</sub> nanowires with good electrical properties.