Geometric structure of Sn dopants in sputtered TiO₂ film revealed by x-ray absorption spectroscopy and first-principles DFT calculations

The crystal structure of tin (Sn)-doped titanium dioxide (TiO₂) film was investigated by using x-ray absorption fine structure (XAFS) measurement and first principle calculations. XAFS measurements suggest that Sn doping can enhance the growth of rutile TiO₂ phase, where Sn ions are considered to substitute into Ti sites with a valence of 4+. First principles calculation reveals that Sn doping can reduce obviously the formation energy of the rutile phase. By comparing the measured and calculated XAFS spectra, we found that the geometric structure of Sn dopant can be understood as the alignment of SnO6 tetrahedrons through a corner oxygen in the Sn-doped TiO₂ film, that is, the Sn ions substituted in the Ti sites and made a one-dimensional zigzag '-Sn-O-Sn-' chain.