Order–order transition structural state in titanium monoxide TiO1.0

Abstract

A new class of defect structures in which point defects of a crystal lattice simultaneously occupy sites of two different superstructures is proposed. The formation of these structural modifications is due to a second-order order–order phase transition that does not occur to the end. The allowable relation between the long-range order parameters in the structural modification formed by a combination of the monoclinic (M 5 X 5)mon (space group C2/m (A2/m)) and the cubic (M 5 X 5)cub (space group Pm3m) of the superstructures is studied using an atom–vacancy ordering in titanium monoxide TiO1.0. The thermodynamic calculations show that the proposed structural modification is equilibrium and must form instead of assumed high-temperature cubic phase (Ti5O5)cub.