Vanadium clusters formation in geometrically frustrated spinel oxide AlVO.

The spinel oxide AlVO is a unique material, in which the formation of clusters is accompanied by atomic, charge and orbital ordering and a rhombohedral lattice distortion. In this work a theory of the structural phase transition in AlVO is proposed. This theory is based on the study of the order-parameter symmetry, thermodynamics, electron density distribution, crystal chemistry and mechanisms of formation of the atomic and orbital structures of the rhombohedral phase.

Phenomenological thermodynamics and the structure formation mechanism of the CuTi₂S₄ rhombohedral phase.

The theory of structural phase transition in CuTi2S4 is proposed. The symmetry of order parameters, thermodynamics and the mechanism of the atomic structure formation of the rhombohedral Cu-Ti-thiospinel have been studied. The critical order parameter inducing the phase transition has been found.

Anion order in perovskites: a group-theoretical analysis.

Anion ordering in the structure of cubic perovskite has been investigated by the group-theoretical method. The possibility of the existence of 261 ordered low-symmetry structures, each with a unique space-group symmetry, is established. These results include five binary and 14 ternary anion superstructures.

Unique atom hyper-kagome order in Na4Ir3O8 and in low-symmetry spinel modifications.

Group-theoretical and thermodynamic methods of the Landau theory of phase transitions are used to investigate the hyper-kagome atomic order in structures of ordered spinels and a spinel-like Na4Ir3O8 crystal. The formation of an atom hyper-kagome sublattice in Na4Ir3O8 is described theoretically on the basis of the archetype (hypothetical parent structure/phase) concept. The archetype structure of Na4Ir3O8 has a spinel-like structure (space group Fd\bar 3m) and composition [Na1/2Ir3/2](16d)[Na3/2](16c)O(32e)4.

High pressure x-ray diffraction study of nickel-copper chromites solid solutions.

A high-pressure synchrotron radiation diffraction study has been carried out on Ni(1-x)Cu(x)Cr(2)O(4) solid solutions. Observed pressure-controlled phase transitions, along with data previously collected for temperature-induced phase transitions, are analyzed in the framework of the unified phenomenological model that results in mapping of the generic phase diagram for the whole family of Ni(1-x)Cu(x)Cr(2)O(4) solid solutions.