On the Topotactic Transformation of Ti2AlC into a Ti-C-O-F Cubic Phase by Heating in Molten Lithium Fluoride in Air

Herein we report on the formation of a TiCOF phase via the topotactic transformation of Ti2AlC by immersion in molten lithium fluoride, LiF, at 900 degrees C in air for 2 h. The Al diffuses out of the structure and reacts with LiF to form Li3AlF6. X-ray diffraction, Raman spectroscopy, optical, scanning and transmission electron microscopy, with energy-dispersive spectroscopy, showed the selective etching of Al from the structure and the formation of a cubic, rock-salt, TiCOF phase. The transformation is topotaxial, involves de-twinning of the hexagonal Ti2AlC structure and results in domains that are of the order of 10 nm. The reaction rate is significantly higher when the reaction is carried out in air than when it is carried out in vacuum.