New Titanium Hydroxyfluoride Ti0.75(OH)1.5F1.5 as a UV Absorber

The microwave-assisted route allows the synthesis of a new Ti hydroxyfluoride adopting a derived form of a ReO 3 -type network. Combined techniques such as (i) powder X-ray and neutron diffraction coupled with electron microscopy; (ii) chemical analysis and density measurements; and (iii) FTIR and TGA analyses support the occurrence of Ti vacancies and the stabilization of hydroxyl groups in the vicinity of Ti 4+ cations. A superstructure of the ReO 3 network has been proposed with two Ti sites and two anionic (OH/F) positions. This original compound exhibits UV-shielding properties with an optical band gap around 3.2 eV and could be considered for potential applications as protective UV absorbers.The O(2p)−Ti(3d) charge transfer band, responsible for this absorption, implies the OH groups and the nonbonding character of the 2p valence band. By changing the synthesis conditions which become reducing, Ti 3+ can be stabilized in this network in an elongated octahedral site as revealed by ESR experiments and UV−visible spectroscopy. This is a second example following the recently prepared Al-based fluoride hydrate with Al vacancies, in which a polarizing cation such as Ti 4+ can accommodate cationic vacancies.