Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. Here we consider such charge storage in a series of oxygen deficient phases of TiO2, known as Magn\'eli phases. These TinO2n−1 Magn\'eli phases present well-defined crystalline structures, i. e., their deviation from stoichiometry is accommodated by changes in space group as opposed to point defects. We show that these phases exhibit intermediate bands with the same electronic quadruple donor transitions akin to interstitial Ti defect levels in TiO2-rutile. Thus, the Magn\'eli phases behave as if they contained a very large pseudo-defect density: 21 per formula unit TinO2n−1. Depending on the Fermi Energy the whole material will become charged. These crystals are natural charge storage materials with a storage capacity that rivals the best known supercapacitors.
@article{arxiv.1602.02849,
title = {Charge storage in oxygen deficient phases of TiO$_2$: defect Physics without defects},
author = {A. C. M. Padilha and H. Raebiger and A. R. Rocha and G. M. Dalpian},
journal= {arXiv preprint arXiv:1602.02849},
year = {2016}
}