Pressure induced amorphisation and the amorphous-amorphous transition in nano-TiO₂: An X-ray Absorption Spectroscopy study

The novel phenomenon of grain-size dependent pressure induced amorphisation (PIA) in TiO₂ nano-materials has been evidenced by several experiments in recent years. The open questions of the structural details of the high density amorphous (HDA) phase have been addressed in a x-ray absorption spectroscopy (XAS) pressure study at the Ti K-edge. The local environment of the cation, to within a few nearest neighbor shells, has been monitored up to -30 GPa where the HDA phase is stabilised. The XAS investigations of this study suggest that a precursor phase is observed before amorphization, the nature of which depends on the experimental conditions. A new structure is stabilized in all cases of samples decompressed from the HDA phase to ambient conditions, characterized by a five-fold coordinated Ti.