A. A. Valeeva

Ordering of Cubic Titanium Monoxide into Monoclinic Ti5O5

The structures of ordered and disordered cubic TixOz= TiOy(y= z/x) phases containing both Ti and O vacancies were studied by x-ray diffraction. The results demonstrate that annealing TiOywith y= 0.9–1.1 below 1300 K leads to the formation of a monoclinic ordered Ti5O5phase (sp. gr. C2/m(A12m/1)). Symmetry analysis of the monoclinic Ti5O5superstructure indicates that the TiOy–Ti5O5ordering transition is defined by the {k10} Lifshits and {k4} and {k1} non-Lifshits wavevector manifolds. The ordering is shown to be a first-order transition accompanied by a decrease in the unit-cell volume of the parent lattice. The Ti and O distribution functions in titanium monoxide are calculated, and the Ti- and O-site near-neighbor environments in the monoclinic Ti5O5superstructure are identified. The region of possible long-range-order parameters is outlined.

Two-sublattice ordering in titanium monoxide

The disordered and ordered structures of nonstoichiometric titanium monoxide TixOz≡TiOy(y=z/x) containing structural vacancies simultaneously in the nonmetallic and metallic sublattices were studied. In the stoichiometry range from TiO0.9 to TiO1.1, an ordered monoclinic phase [space group C2/m (A12m/1)] of the Ti5O5 type is formed in the TiOy monoxide at temperatures below 1300 K. The disorder-order TiOy−Ti5O5 phase-transition channel involves Lifshitz {k10} and non-Lifshitz {k4} and {k11} star rays. The ordering proceeds as a first-order phase transition with a decrease in the volume of the basal cubic lattice. The titanium and oxygen distribution functions in the metallic and nonmetallic sublattices of titanium monoxide are calculated. The domain of allowed values is determined for the long-range order parameter.

Observation of structural vacancies in titanium monoxide using transmission electron microscopy

Structural vacancies were directly observed in nonstoichiometric ordered titanium monoxide using high-resolution transmission electron microscopy under a magnification of 4×106. The observation of structural vacancies became possible due to their ordering and the formation of continuous vacancy channels in certain crystallographic directions. Microdiffraction was employed to orient the sample in the direction permitting the observation of vacancy channels. Transmission electron microscopy providing a magnification of tens of thousands of times revealed that titanium monoxide grains do not contain cracks and macropores and confirmed that the free volume detected picnometrically in the titanium monoxide is concentrated in structural vacancies on the titanium and oxygen sublattices.

Diffraction of electrons in the CubicTi5O5 superstructure of titanium monoxide

Annealed titanium monoxide TiO1.087 has been studied by the electron diffraction method. A cubic model of the Ti5O5 superstructure (Ti5O5 (Ti90▪18O90□18)) of nonstoichiometric titanium monoxide TixOz has been proposed on the basis of experimental data and representations about the disorder-order transition channel. It has been shown that reflections observed on the electron diffraction pattern are identified in the space group

Identification of atomic vacancies in titanium monoxide by electron microdiffraction and positron annihilation

Pm\bar 3m

Observation of structural vacancies

. The period of the unit cell of the cubic Ti5O5 superstructure is larger than that for the B1 basic disordered structure of TixOz monoxide by a factor of 3. The disorder-order transition channel TixOz (space group

Identification and study of vacancies in titanium monoxide by means of positron annihilation techniques

Fm\bar 3m