On the oxidation state of titanium in titanium dioxide

TL;DR

This study challenges the common assumption that titanium in TiO2 is in a +4 oxidation state, providing electronic structure evidence that suggests a lower +3 state based on detailed quantum calculations.

Contribution

The paper offers a comprehensive quantum mechanical analysis indicating that titanium in TiO2 may have a +3 oxidation state, revising the traditional +4 assumption.

Findings

Evidence of significant valence s and d electron contribution

Presence of a nuclear cusp around Ti core

Charge from valence s and d states is approximately 1 e

Abstract

The oxidation state of titanium in titanium dioxide is commonly assumed to be +4. This assumption is used ubiquitously to rationalize phenomena observed with TiO2. We present a comprehensive electronic structure investigation of Ti ions, TiO2 molecules and TiO2 bulk crystals, using different density functional theory and wave function-based approaches, which suggests a lower oxidation state (+3). Specifically, there is evidence of a significant remaining contribution from valence s and d electrons of Ti, including the presence of a nuclear cusp around the Ti core. The charge corresponding to valence s and d states of Ti amounts to 1 e. The commonly assumed picture may therefore have to be revised.