A. I. Potekaev

Effects of Antimony Doping on Electronic Structure of SnO2

Within the framework of the density functional, an investigation is carried out of the electronic structure of stannic oxide and its variations due to antimony doping. It is shown that doping gives rise to formation of an impurity-induced half-filled band below the bottom of the oxide conduction band ensuring the material conduction properties. The changes in the valence band caused by the introduced impurity are in a good agreement with the photoemission data.

Distortion deformations in the B2-R phase transition in titanium nickel alloys

Based on x-ray analysis, we have calculated the lattice distortions in Ti-Ni-Me (Me=Rh, Co, Fe) alloys during the B2-R phase transition. We find that, during the transition, the deformation decreases as the concentration of the alloying component increases in Ti-Ni-Rh and Ti-Ni-Co. No such correlation is observed in the Ti-Ni-Fe alloys.

Role of fractal dimension in internal stress fields of Ni3Fe single crystals

In this paper, using the similarity method we have determined the fractal dimension of the dislocation structure of Ni3Fe single crystals in chaos and in the stage of cell wall formation. We have established that in chaos D=1.04, and at the walls D=1.08. For a linear dependence τ=τf+α·G·b·ρ1/2, the internal stresses increase by a factor of 1.1 in chaos and 1.22 in the cells, while the internal energy increases by a factor of 1.22 and 1.48 respectively. We discuss the mechanisms for roughening the dislocation structure.

Stalking Faults in Non-Equilibrium fcc→18R1 Transformation

Within the framework of the generalized Ising model, the factors stabilizing the 18R1 structure and maintaining the fcc→18R1 transition are established. A computer modeling employed shows that these factors are external shear stress and many-body interactions. The stalking fault density and energy are calculated. Their dependence on temperature and external stress are considered. It is shown that the long-range parameter (in ten coordination spheres) considerably affects the width of the defect region during the 18R1→fcc transition. A comparison is made with the experimental data.

LONG-PERIOD STRUCTURES IN NOBLE-METAL ALLOYS: NEW ASPECTS

Proceeding from precise calculation of the electronic structure and the generalized electronic susceptibility, a systematic study of the relationship between the nesting properties of the Fermi surface (FS) and the character of long-period ordered superstructures (LPSs) in noble-metal alloys, Cu–Au, Cu–Pd, and Ag–Mg, is performed. An answer is provided as to why in Cu–Au, Cu–Pd, and Cu–Pt alloys so-called incommensurate LPSs, characterized by an irrational period and smeared antiphase boundaries, are formed. The reasons for occurrence of such LPSs within a short temperature range only are clarified. The dependence of the long period M on the long-range order parameter η in Cu–Au alloys is accounted for. The causes for formation of two-dimensional LPSs in Au3Cu and Cu3Pd alloys are found. It is shown that their stability may be explained for by energy gaps opening on coinciding patches of FS in two mutually perpendicular directions. Arguments are drawn in favor of the fact that among quasicrystalline substances, phases with incommensurate LPSs occupy an intermediate position between incommensurate systems and quasicrystals. An attempt is made to identify the reasons for qualitatively different behavior of LPSs with large and small superperiods. It is shown that the dependence of LPSs behavior on the value of 2M is controlled by the quality of nesting on FS and the nesting vector sensitivity (2kF) to variations in the long-range order parameter η.

An Electrostatic Approach to Constructing the Atomic Interaction Potentials in Multi-Component Alloys

Based on the classical concepts of metal structure, a semi-empirical model of a metal crystal is proposed. Rather than approximating the interatomic potential type, this model estimates the electron density distribution. Parameters of the electron density distribution of ions in a crystal are also parameters of the interatomic potentials. This method is applicable to the description of properties of both ordered and disordered multi-component alloys.

Behavior of Polytype Structures in Poor-Stability Systems under Varying External Loading

An approach to investigating polytype transformations in close-packed crystals based on the generalized axial finite-dimensional Ising model is proposed. Within this approach, an analysis is made of the influence that model dimensions and long-range and many-body interactions exert on the stability of short-period and multi-layer structures and the sequence of polytype transformations. Using computer simulation techniques, the potential behavior of systems with polytype transformations is studied by varying the external shear stress and temperature under equilibrium and nonequilibrium conditions. The results obtained agree with the experimental data. This approach furnishes a means for predicting new multi-layer polytype structures and determining their symmetry.

Effect of plastic deformation on phase transitions in a Ti50Ni47Fe3 alloy

The results of x-ray structural studies of the effect of previous plastic deformation by rolling on the occurrence of phase transitions in a TiNi(Fe) alloy are presented in the present work. The temperature dependences of the Bragg reflection intensities and half-widths and the dependence of the rhombic angle in the R phase with various degrees of deformation were obtained. Analysis of the results found gave the following rules. Plastic deformation substantially shifts the characteristic temperatures of the martensitic transitions (MT) R-B19′ and B19′-B19″, increases the temperature range of the transformation and can result in a “stepwise” transformation. It was observed that deformation weakly affects the temperature TR for the B2-R transformation.

Combined effect of temperature and pressure on the behavior of long-period ordered structures

The combined effect of temperature and external hydrostatic pressure on the transition of an ordered alloy to a long-period state and characteristics of the structure of the system in the final state are investigated. The energy of the system plays a fundamental role in the formation of a phase with a long period. The external pressure compresses the temperature interval of existence of the long-period state.