Electrochemical Crystal Growth of Titanium Oxyfluorides-A Strategy for Development of Electron-Doped Materials

We report on the growth of single crystals of an electron-doped titanium oxyfluoride, Li2Ti(O,F)(3), employing high-temperature electrolysis of TiO2 with a eutectic Li2MoO4-LiF melt. Greenish octahedral-shaped crystals (similar to 30 mu m in size) with a cubic rocksalt-type structure were successfully obtained by precisely tuning the applied voltage. The temperature-dependent magnetic susceptibility data revealed a paramagnetic behavior at low temperatures, ensuring the presence of Ti3+ ions (mean valence number of +3.78; F/Ti similar to 0.15). The crystals exhibited clear visible-light absorption and produced H-2 from water in the presence of a sacrificial reagent under UV-light irradiation. Li2Ti(O,F)(3) more efficiently produced H-2 compared with a nondoped oxyfluoride Li5Ti2O6F, likely due to the doped electrons for the former. This work highlights a promising electrochemical approach toward growing electron-doped oxyfluoride crystals.