TiNF and Related Analogues of TiO : A Combined Experimental and Theoretical Study.

Aliovalent anion substitution in inorganic materials brings about marked changes in properties, as exemplified by N,F-codoped metal oxides. Recently, complete substitution of oxygen in ZnO by N and F was carried out to generate Zn NF. In view of the important properties of TiO , we have attempted to prepare TiNF by employing an entirely new procedure involving the reaction of TiN with TiF . While the reaction at low temperature (450 °C) yields TiNF in the anatase phase, reaction at a higher temperature (600 °C) yields TiNF in the rutile phase. This is interesting since the anatase phase of TiO also transforms to the rutile phase on heating. The lattice parameters of TiNF are close to those of the parent oxide. Partial substitution of oxygen in TiO by N and F reduces the band gap, but complete substitution increases the value comparable to that of the oxide. We have examined properties of N,F-codoped TiO , and more interestingly N,F-codoped Ti O , both with lower band gaps than the parent oxides. A detailed first-principles calculations has been carried out on structural and electronic properties of N,F-TiO and the TiNF phases. This has enabled us to understand the effects of N,F substitution in TiO in terms of the crystal structure, electronic structure and optical properties.