We report the electronic structure of Mn3O4 postspinel for the first time. In contrast with Mn3O4 spinel, Mn3O4 postspinel adopts a CaMn2O4-type structure with a built-in strain. We conducted both optical measurements and ab initio calculations, and systematically studied the electronic band structures of both the postspinel and spinel Mn3O4 phases. The theoretical electronic structure of Mn3O4 postspinel is consistent with the optical absorption spectra, and both Mn3O4 postspinel and spinel display characteristic band-splitting of the conduction band. The band gap of the postspinel phase is 0.9-1.3 eV smaller than that of the spinel phase. This difference can be explained by the lowering of Mn3+ 3d eg level related to the built-in strain of the postspinel structure. The Mn 3d t2g and O 2p form antibonding orbitals situated at the conduction band with higher energy.
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