Effects of sintering atmospheres on phase transformation, oxygen vacancy and photoabsorption behaviors of highly Fe-doped titania crystals

Fe-doped TiO₂ crystals were successfully prepared using a sol-gel technique in reducing and oxidizing atmospheres. The effects of sintering atmosphere on phase transformation, oxygen vacancy concentration and photoabsorption behaviors were investigated. The results indicate that upon sintering in reducing atmosphere, Ti and Fe ion valences were decreased and highly Fe ions (12 mol%) were entirely dissolved into titania crystals, increasing oxygen vacancy concentration and leading to increased photoabsorption capability. In contrast, sintering in oxidizing atmosphere causes precipitation of the Fe₂O₃ phase, which is detrimental to the photoabsorption capability. The best photoabsorption performance is obtained by sintering 12 mol% Fe-doped TiO₂ in reducing atmosphere, resulting in an absorption edge of approximately 435 nm, which is much higher than that of undoped TiO₂ in the oxidizing atmospheres with the absorption edge 352 nm.