Ordered Structure of Titanium Oxide

Abstract

THE TiO phase in titanium–oxygen alloys is known to have an extraordinarily wide range of composition, that is, from TiO_0.7 to TiO_1.25, and its crystal structure has varying proportions of both titanium and oxygen vacancies. Density and X-ray lattice parameter measurements^1,2 have shown that a third of the oxygen sites are vacant in TiO_0.7, a quarter of the titanium sites are vacant in TiO_1.25 and even in stoichiometric TiO about a seventh of both sites are vacant. According to the X-ray examinations, these vacancies are arranged randomly at temperatures above the equilibrium temperature, 990° C, giving the diffraction patterns typical of a cubic NaCl-type structure. On the other hand, many weak superlattice lines have been observed on the X-ray powder patterns^3,4 after annealing below 950° C, suggesting the formation of an ordered arrangement of vacancies. However, many attempts to determine this ordered structure in terms of an NaCl-type lattice with a periodic vacancy arrangement have been unsuccessful.