Role of stability of the structural state in the change in microcontact spectra of zinc single crystals

This study is devoted to the problem of obtaining microcontacts with a controllable structure and geometry. Laws are established which govern the change in features of microcontact spectra (MCS) in the presence of stable and metastable small-angle twist boundaries in material subjected simultaneously to mechanical loading and a high-density electric field. It is shown that the effect of basis dislocations on the MCS can be discerned thanks to the fact that the field of internal stresses from dislocations pinned in a hexagonal network is considerably greater than the diameter of the microcontact. A quantitative study is made of the parameters characterizing the MCS with a specified structural state in the micro-contraction region. The effect of instability of the structural state resulting from alternating torsion on the MCS is also examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–68, December, 1989.In conclusion, we would like to thank I. K. Yanson for discussing our findings with us.     

Contribution of the multipole polarization to the elastic constants in fluorite structure crystals

Numerical calculations are presented for the contribution of the multipole polarization to the elastic constants in fluorite structure crystals. The multipole polarizability is calculated by the self-consistent field treatment of the local density approximation and the spherical solid model. The elastic constants are significantly affected by the multipole polarization of the ions. The contributions of the multipole polarization of the ions to the elastic constant C₁₁, C₁₂, and C₄₄ are about 25%, 40% and 20% of the experimental values, respectively. The calculated values of the deviation from the Cauchy relation are in good agreement with the experimental values.     

Contribution to magnetisation energy loss separation

The loss analysis is discussed in framework of thermodynamic aspects of magnetisation process. Irreversible changes in energy are described by relaxation and hysteresis effects. Frequency variation of energy is presented using complex plane loci. This concept provides information about the physical aspects of loss separation.     

Free energy and structural phase transitions in mixed crystals: A microscopic derivation

We consider mixed crystals of the form(MY) _x (MX) _1–x , whereY is an active component which drives a structural phase transition, while the componentX has no active internal degree of freedom. We describe this system by a compressible Ising model, including the dilution of the spinsY and the elastic strain fields caused by the componentX. We derive a Landau expansion of the free energy for this system, within molecular field theory. The coefficients of this expansion depend on temperature, pressure, spin concentrationx and the strain fields. This simple model exhibits a rich phase diagram. At sufficiently high concentrationsx, the phase transition is first order. Decreasingx, the transition passes through a tricritical point and eventually becomes second order. For lowx or high strain fields, no transition occurs.     

Contribution of incoherent effects to bremsstrahlung of fast particles in crystals

Incoherent radiation of high-energy electrons in crystals is due to the thermal spread of atoms about their equilibrium positions in lattices. The procedure for modeling incoherent radiation developed previously makes it possible to interpret some results of recent experiments conducted on the Mainz microtron (abbreviated MAMI).     

A symmetry-adapted method for the determination of the lattice energy and properties of ionic crystals

An efficient symmetry-adapted algorithm is described for the calculation of the elastic and dielectric properties of perfect ionic crystals.     

Second-order correction to the positronium ground-state energy in ionic crystals

Upper and lower bounds on the second-order correction to the positronium ground-state energy due to the influence of the crystalline field in an ionic crystal are obtained, and the corresponding formulas are derived. The approximation adopted in the numerical calculations is the model of a point-ion potential. It is shown that neglecting the contribution of states in the continuous energy spectrum of the electron—positron pair to the correction yields an unsatisfactory upper bound. V. I. Lenin Moscow State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 37–41, April, 1998.     

Contribution of collective excitations to the surface energy of metals

We report an RPA-calculation of the high-frequency contribution to the surface energy of metals. Further, on the same basis, we derived the Lifshitz expression for the Van der Waals energy between metallic halfspaces.     

Contribution to the determination of the sensitivity of an ionization transducer

An analytic expression for the coefficient of secondary-electron collection has been obtained for an ionization transducer operating at pressures of 0.5–3 MPa. The coefficient is shown to be limited in the given case by the space charge of the beam being measured. A probability relation has been constructed for the ionization of air by electrons of various energies under normal conditions. A method is described for the calibration of the ionization transducer. The probability of the ionization of the residual gas at the pressures indicated has been determined experimentally.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 18–21, March, 1985.     

Polaron stability in molecular crystals

A semi-empirical Peierls–Holstein model is applied to studies of the stability of polarons in two-dimensional molecular crystal systems. Calculations for a broad range of intra- and inter-molecular parameters within this model were performed in order to obtain detailed knowledge concerning the stability of the polaron solution with respect to a rigid lattice band solution. For realistic values of the parameters the polaron solution is stable with a polaron energy in the range 50–100 meV. A metastable polaron solution is also identified. The polarons that result from our model are highly localized and it is questionable if adiabatic polaron transport can occur in the system.     

Contribution to the electron energy distribution function measurement in the afterglow discharge

The measurement of the higher energy part of the electron distribution function in the neon afterglow is presented. A simple theory which enables us to estimate the error which arises by applying the Druyvesteynian theory to the transition regime is given. The numerical calculations of this error are presented to illustrate the dependence on the various plasma parameters.The author wishes to express his thanks to Doc. dr. M.ícha CSc and Dr. V.Hrachová CSc, for many helpful remarks.     

Dipole-dipole energy in magnetic crystals

The magnetic dipole-dipole energy of a set of magnetic moments on a set of equivalent positions in a collinear magnetic crystal having a magnetic configuration of cubic symmetry is shown to be zero.     

On the stability of hole crystals in layered cuprates

Recent STM measurements have revealed the existence of periodic charge modulations at the surface of certain cuprate superconductors. Here we show that the observed patterns are compatible with the formation of a three-dimensional crystal of doped holes, with space correlations extending between different Cu-O layers. This puts severe constraints on the dynamical stability of the crystallised hole structure, resulting in a close relationship between the periodicity of the electronic modulation and the interlayer distance.Received: 14 June 2004, Published online: 23 December 2004PACS: 74.72.-h Cuprate superconductors (high-T _c and insulating parent compounds) - 71.30. + h Metal-insulator transitions and other electronic transitions - 71.38.-k Polarons and electron-phonon interactions