arXiv subjects
Publications and source records attributed to A. V. Trefilov.
Slow dynamics of energy transfer between different phonon modes under the resonance conditions is considered. It may result in new effects in the inelastic and quasielastic neutron scattering spectra.
A computer simulation of thermofluctuation nucleation of kinks on dislocations and their dynamics is carried out in the framework of two-dimensional (2D) Frenkel-Kontorova model. It is shown that at relatively low temperatures and applied stresses the kinks can appear as a result of developing instability of phonon modes localized in the vicinity of the dislocation. The transition from this mechanism to the ordinary thermofluctuation kink nucleation with temperature increase can reveal itself in the peculiarities of yield stress temperature dependence.
Explicit expressions for anharmonic contributions to the thermodynamic properties with allowance for higher-order phonon-phonon interactions for closed-packed crystals are given, and the calculations for some fcc metals near the melting (Ir, Rh) and martensite phase transition (Ca, Sr) points are carried out. A detailed comparison of anharmonic and electron contributions to the heat capacity of these metals is carried out. The computational results for high-temperature heat capacity agree well with the available experimental data.
The simplest anharmonic characteristics of Ir and Rh are discussed in the framework of a previously developed simple pseudopotential model which describes the elastic moduli, phonon spectra and the lattice heat capacity in the harmonic approximation of these metals succesfully. The microscopic Gruneisen parameters, the dependences of the elastic moduli on pressure, the coefficient of thermal expansion and the equations of state at the finite temperatures have been calculated. The ab initio calculations of the energy-band structure and the equation of state for Ir at T=0 have been done to test the model for adequacy at high pressures. The values of different contributions (zero-point oscillations, quasiharmonic, etc.) in the considered thermodynamic characteristics of Ir and Rh are discussed.
The dispersion in the entire Brillouin zone and the temperature dependence (right up to the melting temperature) of the anharmonic frequency shift and phonon damping in a number of fcc metals is investigated on the basis of microscopic calculations. It is found that the anharmonic effects depend sharply on the wave vector in the directions $Γ$-X, X-W, and $Γ$-L and, in contrast to bcc metals, the magnitude of the effects is not due to the softness of the initial phonon spectrum. It is shown that the relative frequency shifts and the phonon damping near melting do not exceed 10-20%. The relative role of various anharmonic processes is examined, and the relation between the results obtained and existing experimental data is discussed.
The calculations are performed for a broad range of the properties of Ca and Sr in the fcc and bcc phases. A detailed information on the magnitude and character of temperature dependence of anharmonic effects in the lattice dynamics over the entire Brillouin zone (frequency shifts and phonon damping, Gruneisen parameters) is given. A detailed comparison of the computational results for the heat capacity and thermal expansion with the experimental data is carried out; the theoretical results are in good agreement with the experiment.
The equations of state at room temperature as well as the energies of crystal structures up to pressures exceeding 100 GPa are calculated for Na and K . It is shown that the allowance for generalized gradient corrections (GGA) in the density functional method provides a precision description of the equation of state for Na, which can be used for the calibration of pressure scale. It is established that the close-packed structures and BCC structure are not energetically advantageous at high enough compressions. Sharply non-monotonous pressure dependences of elastic moduli for Na and K are predicted and melting temperatures at high pressures are estimated from various melting criteria. The phase diagram of K is calculated and found to be in good agreement with experiment.
General expressions for the contributions of the Van Hove singularity (VHS)in the electron density of states to the thermodynamic potential $Ωare obtained in the framework of microscopic Fermi liquid theory. The renormalization of the singularities in $Ωconnected with the Lifshitz electronic topological transition (ETT) is found. Screening anomalies due to virtual transitions between VHS and the Fermi level are considered. It is shown that, in contrast with the one-particle picture of ETT, the singularities in $Ωturns out to be two-sided for interacting electrons.
A microscopic picture of the ``preparation'' of a crystal to the transition to liquid state at the approach to melting temperature is proposed. Basing on simple crystallogeometric considerations and the analysis of the computational results for corresponding anharmonic characteristics an evaluation is given for the magnitude of atomic displacements leading to the appearance of close packed Bernal pseudonuclei in the solid phase. A physical meaning of the classical Lindeman criterion and the mechanisms of the formation of free volume in the crystal phase are discussed.
Numerical simulation of the dislocation motion in 2D Frenkel - Kontorova (FK) model in the thermostat shows an unusual dynamical behavior. It appears that ''kink'' regime of dislocation gliding takes place in a certain region of parameters of the model but, in disagreement with the common views about the dislocation motion under plastic deformation condition, the kinks appear to be similar to sine-Gordon solitons despite the discreteness of the lattice, damping and thermal fluctuations. At high enough stresses and temperatures the motion of the dislocation is accompanied by its oscillations rather than kink nucleation.
A simple pseudopotential model is proposed, which allows the phonon spectra and temperature dependence of the lattice heat capacity of Ir and Rh be described with a high enough accuracy. A careful comparison of the calculated and experimental values of the lattice heat capacity is carried out, with the procedure of the identification of the phonon contribution to the heat capacity and determination of the characteristics (momenta) of the phonon density of states from the experimental values of the total heat capacity of metal at a constant pressure being described in detail. The results of the theoretical calculations explain, in particular, such peculiar feature of Ir and Rh, unusual for cubic metals, as a sharp (more than by a factor of 1.5) decrease in the effective Debye temperature with increasing termperature. The temperature dependence of the mean square amplitude of atomic displacements in Ir and Rh has been calculated. Basing on the band calculations the manifestation of the Kohn singularities in the phonon spectra of Ir are discussed.
An accurate numerical consideration is carried out of the ground state for the simplified model which is traditionally used for the description of Verwey transition and related phenomena. In the framework of 1D spinless fermion model, the effects of next-nearest neighbour (NNN) interaction on the metal-insulator transition are investigated for electron concentrations 1/2 and 2/3. It is shown that for large enough NNN transfer integrals the electronic topological transition of metal-metal type is also possible. The corresponding phase diagrams are presented.
To describe structural peculiarities in inhomogeneous media caused by the tendency to the close packing of atoms a formalism based on the using of the Riemann geometry methods (which were successfully applied lately to the description of structures of quasicrystals and glasses) is developed. Basing on this formalism we find in particular the criterion of stability of precipitates of the Frank-Kasper phases in metallic systems. The nature of the ''rhenium effect'' in W-Re alloys is discussed.