Efficiency of Generation of Surface Acoustic Waves in Barium Strontium Titanate Thin Films.

The excitation of surface acoustic waves (SAWs) on the surface of the ferroelectric film [barium strontium titanate (BST)] located on the dielectric substrate (silicon) was studied theoretically. We found that the most effective SAW excitation takes place when spontaneous polarization occurs in the film plane and the wave propagates along the direction adjacent to the direction of the spontaneous polarization vector. Based on a nonlinear model of phase transitions in solid BST solutions, the dependency of the material constants of piezo-effect equations on the misfit strain with a fixed concentration was obtained numerically.

Phase transitions in BiTiO.

BiTiO is a representative of the Aurivillius family of layered perovskites. These are high-temperature ferroelectric materials with prospects for applications in random-access memory and are characterized by an extremely confused interaction of their structural degrees of freedom. Using group-theoretical methods, structural distortions in the BiTiO high-symmetry phase, caused by rotations of rigid octahedra and their displacements as a single unit, have been investigated, taking into account the connections between them.

Tunable Electromechanical Properties of a Barium Strontium Titanate Ferroelectric Film Under a Uniaxial Stress.

The possibility of the development of MEMS devices based on the tunable ferroelectric film Ba Sr O properties under uniaxial deformation was studied theoretically. The thermodynamic model of the phase transitions for the film under uniaxial stress was constructed. The behavior of the material constants for the film in various phase states was investigated.

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.