Cooperative Characterization of In Situ TEM and Cantilever-TGA to Optimize Calcination Conditions of MnO 2 Nanowire Precursors.

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 in situ TEM in collaboration with microcantilever-based thermogravimetric analysis (cantilever-TGA) techniques. The morphological evolution of precursors under atmospheric conditions is observed with in situ TEM, and the right calcination temperature is provided by cantilever-TGA. The proposed approach successfully optimizes the calcination conditions of fragile MnO 2 nanowire precursors with multiple valence products. The cantilever-TGA shows that a calcination temperature above 560 °C is required to transform the MnO 2 precursor to Mn 3 O 4 under an N 2 atmosphere, but the in situ 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 2 -containing atmosphere can produce Mn 3 O 4 nanowires with good electrical properties.