Study of electronic structure of reduced TiO2 and VxTi1−xO2 crystals by ESCA and optical absorption

An analysis is made of optical absorption spectra and electron spectroscopy for chemical analysis (ESCA) on pure TiO2, reduced TiO2, and VxTi1−xO2. It is found that in the reduced TiO2, the Ti ion takes the variable valence states, Ti4+, Ti3+, and Ti2+, and they form a broad donor band, which overlaps with the conduction band originating from Ti4s levels. 3d–4s mixing results in a large change of the conductivity of TiO2 from insulator to metal depending upon the degree of reduction. In TiO2 doped with V, which behaves like a free ion, the excess 3d electrons of the V ions form impurity level just above the O2p valence band. In the reduced VxTi1−xO2, four different valence states, Ti4+, Ti3+, Ti2+, and V4+, are found and this accounts for the narrow optical gap of this material.