Abstract
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 Magnéli phases. These Magnéli phases (TinO2n−1) 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 an electronic quadruple donor transitions akin to interstitial Ti defect levels in rutile TiO2. Thus, the Magnéli phases behave as if they contained a very large pseudo-defect density: ½ 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.
Highlights
Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications
These can be considered as oxygen-deficient phases of TiO2, but the off-stoichiometry is accommodated by changes in the crystal structure, manifested as shear planes, as opposed to point defects, such as oxygen vacancies or Ti interstitials
The stoichiometric phases of this material, rutile, anatase, and brookite TiO2 are known to present unintentional n-type doping at ambient conditions, owing in part to intrinsic point defects related to oxygen deficiency: oxygen vacancy (VO) and titanium interstitial (Tii)[16,17,18]
Summary
Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. These can be considered as oxygen-deficient phases of TiO2, but the off-stoichiometry is accommodated by changes in the crystal structure, manifested as shear planes, as opposed to point defects, such as oxygen vacancies or Ti interstitials.
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