Structure of molten titanium dioxide

The xray structure factor of molten TiO[sub 2] has been measured, enabled by the use of aerodynamic levitation and laser beam heating, to a temperature of T = 2250(30) K. The TiO[sub 2] liquid is structurally analogous to the geophysically relevant high pressure liquid silica system at around 27 GPa. We argue that the predominance of fivefold polyhedra in the melt implies the existence of as-yet-undiscovered TiO[sub 2] polymorphs, based on lower-than-octahedral coordination numbers, which are likely to be metastable under ambient conditions. Given the industrial importance of titanium oxides, experimental and computational searches for such polymorphs are well warranted.