, Volume 55, Issue 11, pp 2346-2352
Date: 13 Jul 2012

Thermal transformation of δ-MnO2 nanoflowers studied by in-situ TEM

Abstract

In-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor variations of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upon thermal annealing at elevated temperatures up to ∼665 °C. High-temperature annealing drives the diffusion of the small δ-MnO2 nanocrystallites within short distances less than 15 nm and the fusion of the adjacent δ-MnO2 nanocrystallites, leading to the formation of larger crystalline domains including highly crystalline nanorods. The annealed nanoflowers remain their overall flower-like morphology while they are converted to α-MnO2. The preferred transformation of the δ-MnO2 to the α-MnO2 can be ascribed to the close lattice spacing of most crystalline lattices between δ-MnO2 and α-MnO2, that might lead to a possible epitaxial growth of α-MnO2 lattices on the δ-MnO2 lattices during the thermal annealing process.