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First-principles studies of the atomic, electronic and magnetic structure of alpha-MnO2 (cryptomelane)

Published

Author(s)

Eric J. Cockayne, Lan (. Li

Abstract

First-principles density functional theory calculations are used to investigate alpha-MnO2, a structure containing a framework of corner and edge sharing MnO6 octahedra with tunnels in between. Calculations show that placing additional species, such as K+ ions,into the tunnels can stabilize alpha-MnO2 with respect to the rutile-structure beta-MnO2 phase,in agreement with experiment. The determined magnetic structure has antiferromagnetic Mn-Mn interactions between corner-sharing octahedra and ferromagnetic Mn-Mninteractions between edge-sharing octahedra, but long-range magnetic order is only expected at cryogenic temperatures. Pure alpha-MnO2 is found to be a semiconductor with an indirect band gap of 1.3 eV. The main effect of placing ions such as K+ inside the tunnel is to shift the Fermi level. Water and related hydrides (OH-; H3O+) can also be accommodated in the tunnels. When both K+ and an oxygen hydride are present in the tunnel, the K-O distance increases with increasing oxygen hydride charge, as expected from electrostatics.
Citation
Chemical Physics Letters
Volume
544

Keywords

manganese oxide, cryptomelane, oxide magnetism, octahedral molecular sieve materials

Citation

Cockayne, E. and Li, L. (2012), First-principles studies of the atomic, electronic and magnetic structure of alpha-MnO2 (cryptomelane), Chemical Physics Letters, [online], https://doi.org/10.1016/j.cplett.2012.06.061 (Accessed July 17, 2024)

Issues

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Created July 4, 2012, Updated October 17, 2022