bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation of superconductivity in ceramic oxides
Authors: Saif A. G. , Chela‐Flores J.
Published: July 2007

The nucleation of superconductivity in the interior of a bulk specimen, as well as at the surface of ceramic superconductors is discussed on the base of phenomenological equations, in which superconductivity coexists with antiferromagnetism. The prediction of the evolution of Hc2 with small variations on the coupling constant may serve to test the underlying phenomenological theory.
Spin kinetics in paramagnets at low temperature
Authors: Tayurskii D. A.
Published: July 2007

An analysis is made of some thermodynamic properties of the spin system of a diluted paramagnetic crystal and stationary saturation, electronic and nuclear spin‐lattice relaxation, and the influence of phonon bottleneck at low temperatures (Zeeman energy larger than heat) are investigated.
Dispersion properties of submicron‐thin CdS crystals
Authors: Reznichenko V. Ya. , Strashnikova M. I. , Cherny V. V.
Published: July 2007

The data are summarized, obtained by interference measurements at 4.2 K, on the dispersion of the refractive index n(λ) of submicron‐thin CdS single crystals. The series of the dispersion curves, n(λ), measured for crystals of different thickness, is approximated by theoretical dependences allowing for spatial dispersion. These data present clear evidence that the refractive index depends on the thickness of crystals provided their dimensions are comparable with the wavelength of light or smaller than the latter.
Frequency‐modulation optical spectroscopy of niobium. Theory and experiment
Authors: Magnitskaya M. V. , Kulikov N. I. , Shelekhov A. L.
Published: July 2007

Both, experimental and theoretical investigation are made of frequency‐modulated optical spectrum of Nb. The experimental spectra are measured in the range of light energy from 1 to 6 eV. The theoretical studies are performed in the framework of density functional formalism using the linearized hybridized KKR (LHKKR) method for self‐consistent calculations of band structure and wave functions. A reasonable coincidence between theoretical and experimental results is obtained.
Continuum Approximation of the General Inverse‐Power Lattice Sums in Cubic Crystals
Authors: Turner M. D. , Mohazzabi P.
Published: July 2007

The continuum approximation of Born and his collaborators for the calculation of simple lattice sums in cubic crystals is extended to the case of general lattice sums. The results show excellent agreement with the exact values across the board, thus providing a ground for further applications of the continuum model.
Stark Effect and the F‐Center Excited States
Authors: Ponnambalam M. J.
Published: July 2007

Using a simple model of the F‐center, it is shown that whether the |2Γ〉 state is above or below |2Γ〉 in emission is not quite clear from the existing Stark data. In light of this, the relative merits of the different Stark effects are critically analyzed. It is shown that fresh data on the field‐induced changes in the radiative life‐time can unambiguously settle the relative position of the |2Γ〉 state with respect to |2Γ〉.
The Theory of Elastic Wave Propagation in Inhomogeneous Media
Authors: Fokin A. G. , Shermergor T. D.
Published: July 2007

The theory of longitudinal and transverse elastic waves is considered within the framework of random field theory. A method is developed for solving problems associated with the scattering of waves by inhomogeneities of the density ϱ(r) and of the elastic modulus tensor λ(r) which is valid for the whole wavelength range. The scattering index γ, the phase v, and the group velocities c are computed using the Bourret approximation with allowance for spatial dispersion. Asymptotic expressions for γ, v, and c are obtained for the long (compared with the effective sizes of the scattering regions), short, and ultrashort wave ranges. In the latter case results can be obtained only by allowing for spatial dispersion.
Ferroelectric Phase Transition in (NH4)2BeF4. Possibility of Molecular Distortion Type of Transition
Authors: Bajpai P. K.
Published: July 2007

The possibility of molecular distortion type (MD‐type) microscopic mechanism (recently proposed for (NH4)2SO4) and the role of BeF ion in the phase transition of amonium fluoberryllate are examined by analysing crystal structural data in both, the paraelectric and ferroelectric phases. The results show that BeF ion attains a dipole moment in the FE phase and contribute significantly to the spontaneous polarisation (Ps). The computed value of Ps due to NH and BeF ions (0.21 μC/cm2) matches satisfactorily with the experimental results. The nature of the phase transition is found to be mainly of MD‐Type. The soft mode of the transition is proposed as a mixed mode having the internal mode of BeF ion and translatory modes of NH ions.
Spinodal Decomposition in Semiconductor Alloys
Authors: Dugaev V. K. , Petrov P. P.
Published: July 2007

A generalization is proposed of the lattice gas model which takes into account the presence of free Fermions in the system. In the framework of this approach the Landau free energy expansion is constructed. The influence of the electron energy spectrum particularities on the spinodal decomposition in the semiconductor alloys is examined.
On the Band Structure of Ultrathin Layer Semiconductor Superlattices
Authors: Gushchina N. A. , Nikulin V. K. , Tzarev Yu. N.
Published: July 2007

A band structure calculation of (GaAs)m(AlAs)m superlattices with m = 1, 2, 3, 4 is made by the recursion method in the Bloch sum basis. A dependence of the direct band gap width E on thickness m of the alternating layers is obtained which agrees well with other calculations and experimental photoluminescence data. The scheme of determination of the sp3s* Hamiltonian parameters proposed earlier is modified which affects significantly the results for the band discontinuities at the GaAs/AlAs heterojunction and for the “local” band gap width Eg of superlattices obtained from an analysis of the local density of electron states averaged over the layers parallel to the interface. A comparison of the lattice‐averaged band gap width E with the local width Eg shows that the latter yield an underestimated value for the gap width.
Polarons in Trans‐Polyacetylene and Polyyne Chains
Authors: Osipov V. A. , Bochnacka G. , Fedyanin V. K. , Malek J.
Published: July 2007

The polaron formation in trans‐polyacetylene as well as polyyne chains is investigated in the framework of the finite‐band scheme. The physical characteristics of polarons (spin, charge, formation energy, width, binding energy) are calculated. The bipolaron, tripolaron, and polarexciton states in polyyne are considered. A self‐consistent discrete analysis of polaron states is presented. Comparison between the finite‐band and discrete calculations is done.
Plasmon Dispersion in Trans‐Polyacetylene
Authors: Haase M. , Taut M.
Published: July 2007

By frequency momentum analysis, the plasmon dispersion of crystalline trans‐polyacetylene is calculated for q parallel and perpendicular to the chains. Both experimentally observed features: linear dispersion at medium q, and a drop for small q, are obtained. It is suggested that the latter feature is much more pronounced for q perpendicular to the chains (not investigated experimentally) than parallel.
Longitudinal Thermogalvanomagnetic Effects in Dilute Magnetic Semiconductors in a Quantizing Magnetic Field
Authors: Lyapilin I. I. , Karyagin V. V.
Published: July 2007

The temperature and magnetic field dependence of the longitudinal thermogalvanomagnetic coefficients in dilute magnetic semiconductors is calculated in a quantising magnetic field using Kubo's formula.
On the Mechanism of Vibrational Relaxation of Two‐Centre Excitions in Solid Neon
Authors: Fugol I. Ya. , Ratner A. M. , Rybalko Yu. I. , Steshenko Yu. L.
Published: July 2007

The population of vibrational levels of the lowest‐lying excimer term in solid neon is reproduced in the experimental luminescence spectra. The analysis of the kinetic equation suggests that the reproduced population can be caused by the vibrational relaxation only in the case of a great heat relase due to the two‐centre excitation jumps through the lattice.
Exotic Glassy Phase in the Site‐Diluted Transverse Ising Model at Zero Temperature ?
Authors: Busiello G. , de Cesare L. , Lukierska‐Walasek K. , Walasek K.
Published: July 2007

A self‐consistent diagrammatic approach is used for studying the zero‐temperature properties of the three‐dimensional site‐diluted transverse Ising model via a path‐integral representation. It is found, that the peculiar competition between random and quantum fluctuations inhibites the occurrence of a second‐order phase transition and an exotic phase with some spin‐glass‐like characteristics appears. This should provide a plausible explanation of recent experiments on some mixed crystals.
Theoretical Description of Light Diffraction on Acoustic Pulses in Bragg's Region
Authors: Bodzenta J. , Kleszczewski Z.
Published: July 2007

As a result of theoretical analysis an equation is obtained describing the dependence of deflected light intensity on diffraction angle and time. Considerations are carried out for an isotropic, nonmagnetic dielectric medium and Gaussian light beam. The inverse problem is solved, too. Basing on its solution an acousto‐optic method for acoustic pulse parameter analysis is proposed. It allows to reconstruct the acoustic wave envelope basing on the diffraction pattern. This method may be used in investigations of acoustic properties of solids and liquids.
The Investigation of the Ferroelectric Phase Transition in Cluster Systems of Order–Disorder Type
Authors: Yukhnovskii I. R. , Korynevskii N. A.
Published: July 2007

The description of second‐order ferroelectric phase transitions in cluster systems of order–disorder type in the frames of the collective variables method is proposed. By means of the canonical Hubbard operator technique the Ising‐like form of the Hamiltonian is obtained. The partition function is represented as a functional integral over collective variables. The classification of collective variables according to their role in forming of the ferroelectric order parameter is made. For a consistent consideration of critical fluctuations of the order parameter a non‐Gaussian, quartic basic measure density is obtained.
Lineshape of Light Absorption by Thermalized Frenkel Excitons under Band‐to‐Band Transitions
Authors: Grigorchuk N. I. , Grechko L. G.
Published: July 2007

It is assumed that sublevels of the lowest exciton band in consequence of pumping are filled by excitons, which thermalize during their lifetime. The probability of throwing of such excitons to the next more higher lying band by means of another radiation source is investigated. By simple assumptions, when the distance between the exciton bands is much greater than the bandwidth difference and the damping parameter is independent of the frequency, the lineshape of light absorption under band‐to‐band transitions is calculated. For small damping in the case of broad bandwidth it is shown that the absorption is determined rather by temperature of the crystal than by bandwidth difference. In the case of narrow bands only that difference plays the essential role.
Nature of Hydrogen Bonding in Si‐A‐Center
Authors: Gutsev G. L. , Myakenkaya G. S. , Frolov V. V. , Glazman V. B.
Published: July 2007

The configurations containing one or two hydrogen atoms in a A‐center are calculated by the MNDO and Xα‐DV methods. It is established that the hydrogen atom is bound with the oxygen of the A‐center forming a new paramagnetic center. The electrical activity of the A‐center is decreased by hydrogen passivation of the two silicon dangling bonds. However, the defect states are not removed from the band gap.
Localized States in Crystalline Semiconductors
Authors: Kouimtzi S. D.
Published: July 2007

Hopping conduction is studied in crystalline Si, Ge, InSb, GaAs, and InAs. Sufficient degree of damage induced by electron irradiation allows the observation of conductance by nearest neighbour hopping, or variable range hopping. Evidence of electron‐electron interaction in the hopping conductance is presented.
Antiferromagnets with Random Anisotropy. Influence of the Dimensionality
Authors: Richter J. , Skomski R.
Published: July 2007

The influence of a small random anisotropy on the ground‐state properties of a classical antiferromagnet with an easy z‐axis in two, three, and four dimensions is discussed. The random anisotropy causes a slightly noncollinear magnetic structue, in which the tipping of the sublattice magnetisations varies over the system. The tipping is largest in two dimensions and decreases rapidly with increasing dimension. The magnetisation‐versus‐field behaviour is strongly influenced by the random anisotropy in the case of fields parallel to the easy z‐axis and close to the spin‐flop transition for dimensions two and three. A smearing out of the spin‐flop transition is indicated, which is particularly pronounced in two dimensions. The dimension four is the marginal dimension, where the small random anisotropy is almost negligible against the coherent part of anisotropy.
Hyperfine Fields at Implanted 12Boron in F.C.C. Metals
Authors: Tompa K. , Pirlot R. , Grenacs L. , Lehmann J.
Published: July 2007

Knight shift data of implanted 12B are used to estimate hyperfine field, Hhf(s), and Knight's ξ factor for Al, Cu, Ag, and Au metals at the boron site. In the Rh, Pd, and Pt transition metals the Knight shift and the Korringa relaxation time T1e are used to estimate the s and d terms of the hyperfine field. In addition to the data from the literature T1e is measured in Rh metal, and it is proved experimentally that in Rh, Pd, and Pt over T1e there is no other spin–lattice relaxation mechanism around room temperature. The hyperfine fields at the boron are compared with those at the muon (+) in these metals.
Raman Spectroscopy of Soft and Rigid Modes in Ferroelectric TlInS2
Authors: Burlakov V. M. , Ryabov A. P. , Yakheev M. P. , Vinogradov E. A. , Melnik N. N. , Gasanly N. M.
Published: July 2007

Low‐frequency Raman spectra of a TlInS2 single crystal in the vicinity of a ferroelectric phase transition are reported. In the ferroelectric phase a soft mode interacting with some rigid modes is observed. The temperature dependence of the soft mode frequency is found to be proportional to (Tc – T)1/2. An unusual behaviour of the rigid mode (ω = 20 cm−1) is observed. This fact is interpreted in terms of inherent lattice defects which cause nonhomogeneous broadening.
Triplet Molecular Excitations in Potassium Halide Cyanide Crystals. II. The K(CN)xCl1–x Mixed System
Authors: Camargo S. S. , von der Weid J. P.
Published: July 2007

The decay kinetics and luminescence intensity of the UV emission associated with the a3II → X1Σ+ electronic transitions of the CN– molecular ions in K(CN)xCl1–x mixed crystals are investigated between 10 and 450 K. At the lowest temperatures the emission lifetimes as functions of the CN– concentration x show a transition between localized and collective behaviours around the percolation threshold for the CN– sublattice. A low temperature non‐radiative decay process is observed and is attributed to the coupling of the relaxed excited states of CN– clusters to translational–rotational cyanide‐like phonon modes.
Dislocation Arrangements in Stress Gradients
Authors: Hu Xiaoyu , Margolin H.
Published: July 2007

The equilibrium positions of screw and edge dislocations moving in a stress gradients, after emission from source, are determined for groups of 10 to 50 dislocations for various stress gradients and distances between the source and the position where the critical resolved shear stress is located.
On the Determination of Enhancement Factors of Solvent Diffusion
Authors: Hagenschulte H. , Heumann Th.
Published: July 2007

In dilute binary f.c.c. alloys of the substitutional type a nonlinear increase of the solvent diffusion coefficient D by alloying solutes with positive excess charge is frequently observed. The formation of vacancy–impurity complexes leads to this increase, which is usually described in terms of the enhancement factors bi in the following manner: D(NB) = D(0) (1 + b1NB + b2NB2 + + b3NB3 + …). The determination of enhancement factors by using this polynomial is critically discussed. From the complex model according to Dorn and Mitchell and more generally according to Bérces and Kovács and its application to solvent diffusion by Hehenkamp et al. it becomes reasonable, that the dependence of the solvent diffusion coefficient on the solute concentration is approximately given by: D(NB) = D(0) exp (b1NB). This relation, which is already known in the literature for a long time, yields an alternative method for the detemination of enhancement factors. Results are presented for many noble metal systems and discussed in the frame of two different estimation methods of the Gibbs free energy of binding δg1 of a vacancy–impurity pair calculated from the enhancement factors b1 and b2.
The Effect of Stress on the Lattice Instability of a TiNi Alloy
Authors: Li D. Y. , Wu X. F. , Ko T.
Published: July 2007

The behavior of the phase transformation in equiatomic TiNi alloy during thermal cycling under applied stresses is studied by measuring the electical resistivity and investigating the diffuse streak diffraction of electron and the X‐ray diffraction. The results show that the stress has a strong effect on the lattice instability. The tensile stress promotes the softening of phonon modes which relate to the nucleations of the R phase and the martensitic phase so that the tensile stress is favourable for the formation of the R phase and martensitic phase, while the compression stress has negative effects. The investigation shows that the effect of stress on 〈111〉 longitudinal phonon mode is larger than that on 〈110〉 transversal phonon mode. The tensile stress enhances particularly the softening of 〈111〉 longitudinal phonon mode which corresponds mostly to the R phase transformation, but the compression stress is unfavourable for it. It is identified that the diffuse streak diffraction patterns of electron associated with more R phase induced by the tensile stress arises from the softening of 〈111〉 longitudinal phonon mode.
A Hamiltonian Model of Liquefaction and Crystallization in Three Dimensions
Authors: Maćkowiak J.
Published: July 2007

A model of a classical gas on a three‐dimensional sphere is discussed. The sphere is partitioned into cells, each corresponding to a different particle. The potential of each particle in its own cell is zero and, outside the cell, of order ln n, n being the number of particles. The two‐body interaction between the particles is shown to provoke (in the thermodynamic limit) a gas–liquid phase transition and a liquid–solid transition at a lower temperature. Both transitions are accompanied by a discontinuous drop of entropy.
Dispersion Curves of Phonon‐Plasmon Coupled Polaritons in n‐Type AlxGa1−xAs
Authors: Chang C. P. , Pai K. F. , Fang C. S. , Tse W. S.
Published: July 2007

The dielectric constant method is used to calculate the dispersion curves of phonon‐plasmon coupled polaritons in n‐type AlxGa1−xAs. The method is based on the assumption that the polarisabilities of the ion system and the electron system are additive. The conventional additive form is used for the dielectric function of the lattice. The Lindhard dielectric function is used for the dielectric constant of the electron gas in the system. The polariton‐mode frequencies are derived by equating the total dielectric function to c2q2/ω2, where c2 = 1/μ0ε0, q the wave number, and ω the frequency. The reflectivity spectra of n‐type AlxGa1−xAs are also presented.
Thermodynamics of the Phase Transition Sequence in the Incommensurate Compound (N(CH3)4)2CuBr4
Authors: López‐Echarri A. , Ruiz‐Larrea I. , Tello M. J.
Published: July 2007

The prototype‐incommensurate‐ferroelectric‐ferroelastic phase transition sequence in (N(CH3)4)2CuBr4 is studied by adiabatic calorimetry in the temperature range 60 to 343 K. The thermodynamic function values assigned to the successive phase transformations permit a comparative study with other tetramethylammonium tetrahalogenmetallates. The enthalpies involved in their phase transition sequences can be related to the packing of the crystal unit cell and to the position of each compound in a common pressure‐temperature phase diagram. In the case of (N(CH3)4)2‥CuBr4, this diagram is correctly described by a simple phenomenological model. A brief discussion on the critical exponents associated to the specific heat (α = α′ = 0.01 for ‖T − T0‖ < 0.2 K) and to the order parameter, for the prototype‐incommensurate phase transition, is also included.
Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. I. The Cubic‐Orthorhombic Phase Transition of Pure Potassium Cyanide
Authors: Yang Zhengju , Luty F.
Published: July 2007

The kinetics of elastic ordering of KCN controlled by a thermally activated process is studied by considering the interaction between elastic CN− dipoles. The lattice constants obtained and reorientational activation energy of dipoles in the elastically ordered lattice agree quantitatively with experiments. The calculation indicates that the orientation ordering of elastic dipoles is induced by the strain field due to ordering alignment of dipoles. The elastic interaction between close neighbors of dipoles has little influence. The first‐order character of the phase transition is obtained, and it is found that an initial degree of order depending on the temperature is necessary to start the ordering process. It is concluded that this corresponds to the nucleation process of the first‐order phase transition.
Electronic Structure and Properties of Boron Phosphide and Boron Arsenide
Authors: Prasad C. , Sahay M.
Published: July 2007

The composite wave variational version of the APW method is used to obtain the electronic band structure of the compounds boron phosphide and boron arsenide at the high symmetry points Γ, X, and L. The tight binding interpolation scheme of Slater and Koster is used to calculate the rest of the band structure. The results show that both these materials are indirect band gap semiconductors. The density of states, and the imaginary part of the dielectric constant is also calculated. The theoretical results are compared with the reported experimental and theoretical data.
The Quadratic Response of a Fermi Gas for Arbitrary Degree of Degeneracy
Authors: Pickenhain R. , Flietner B. , Unger K.
Published: July 2007

The diagonal quadratic response function of a non‐interacting Fermi gas is generalized to arbitrary degrees of degeneracy. The validity of a simplified quadratic response function proposed earlier, is analyzed in detail. Hints to its applications are given.
The Superconductor Glasses (SuG). A Fractal Description
Authors: Giovannella C.
Published: July 2007

It is shown that the value of the 1/Ψ critical exponent measured on sintered high‐Tc granular superconductors (La1.85Sr0.15CuO4−δ and YBa2Cu3O7−δ) can be understood within the framework of a fractal model. Using the fractal cluster model, it is shown that under the hypothesis of ν = 1.33, the fractal dimension of these systems can be always straightforwardly derived. The comparison between the values of the SuG critical exponents and those of the spin glasses (SG) suggests the inclusion of both the ensembles of critical systems in a unique universality class whose definition differs from the usual one.
Electronic Properties of the Defect Perovskite System La1−xLixMO3
Authors: Bahadur D. , Bilas Ram , Murty B. S. R.
Published: July 2007

The systems La1−xLixFeO3 for x values up to 0.5 are synthesised and found to be monophasic with rhombohedral and orthorhombic symmetry, respectively. Unlike for Sr2+ substitution, these samples do not become cubic for higher x values. The electron transport in these systems is discussed in terms of variable valence and spin states and the band picture. Improvements in the magnetisation values in the system La1−xLixFeO3 are attributed to disordering of spins and lowering of symmetry around Fe3+ due to substitution and oxygen vacancy.
Charge Transport in FeCl3‐Doped Polyethylenevinylacetate–Polyoctylthiophene Blends
Authors: Isotalo H. , Laakso J. , Kuivalainen P. , Stubb H. , Österholm J.‐E. , Yli‐Lahti P.
Published: July 2007

The results of an experimental study of the temperature (T) dependent dc conductivity σdc, T‐dependent thermoelectric power (TEP), and electron spin resonance in a new conducting polyethylenevinylacetate–polyoctylthiophene (EVAPOT) polymer blend doped with FeCl3 are presented. For a POT content of 20 wt% σdc (300 K) varies from 10−10 to 1 Ω−1 cm−1 with increasing doping, while σdc(T) fits σdc(T) = σ0 exp [– (T0/T)1/2], especially in highly conducting material. In the most heavily doped samples TEP shows metallic behaviour and the charge transport is described by the granular metal model. In lightly doped samples the T‐dependence of TEP follows the T−1‐law for band conduction in non‐degenerate crystalline or amorphous semiconductors. This is the first time the latter behaviour is found in conducting polymers.
Electron Transport in Quasi‐Two‐Dimensional Systems. Influence of Intersubband Scattering
Authors: Pratsch Chr. , Suhrke M.
Published: July 2007

The temperature and electron concentration dependence of the electron mobility is calculated for single quantum wells considering two occupied electron subbands. The results for the different scattering mechanisms and their interplay in the total mobility are changed with respect to those of other theoretical approaches which neglect multisubband coupling. The influence of the intersubband scattering is analyzed and the results are in agreement with experimental data.
Anomalous Behavior of the Low‐Temperature Spin Disorder Resistivity in PrH2+x Compounds
Authors: Daou J. N. , Burger J. P. , Vajda P.
Published: July 2007

Pure PrH2 dihydride presents an antiferromagnetic transition at 3.35 K; above TN, a decrease of the resistivity ϱ(T) is observed which can be explained by a Kondo effect but also by crystal field effects if the first non magnetic excited state Γ1 it situated very near to the magnetic Γ5 ground state. Magnetic ordering and the resistivity minimum disappear in PrH2+x compounds when x ≫ 0.08; this can be explained if there is an inversion of the Γ5 and Γ1 states or if there is a splitting of the triplet Γ5 state due to a tetragonal deformation of the lattice. Anomalous values of the low temperature slope dϱ/dT seem to correlate with the occurrence of this cubic‐tetragonal transformation of the host lattice.
ESR Studies of Single Crystals of Bis(ethylenedithio)tetrathiafulvalene‐Based Conductor with Octaiodinemercurate Anion (BEDT‐TTF)4Hg3I8
Authors: Firlej L. , Graja A. , Wolak J. , Lyubovskaya R. N. , Goldenberg L. M.
Published: July 2007

The electron spin resonance g‐value, linewidth, and spin susceptibility of single crystals of bis‐(ethylenedithio)tetrathiafulvalene‐based conductor with octaiodinemercurate anion, (BEDT‐TTF)4Hg3I8, are found to show pronounced temperature dependences in the T‐range from 20 to 300 K. A first‐order phase transition of the type semiconductor–semiconductor is observed at 265 K; it is associated with ordering of HgI4 tetrahedra in the crystal lattice. Discussion of the line‐shape and other ESR parameters is given.
Electromagnetic Wave Scattering in Inhomogeneous Media with Spatial Dispersion
Authors: Fokin A. G. , Shermergor T. D.
Published: July 2007

The problem of electromagnetic wave scattering on inhomogeneities of the dielectric permittivity tensor εij  εij(r) is considered. It is shown that effects caused by the coordinate dependence of εij can be studied by means of analyzing properties of the Fourier transform of the effective dielectric permittivity tensor ε(k). This fact makes it possible to develop a unified approach to solving the problem of electromagnetic wave attenuation and phase an group velocity variations caused by the scattering. The scattering index γ, phase velocity ν, and group velocity c are calculated within the framework of the Bourret approximation in all ranges of wavelengths. Asymptotic expressions for γ, ν, and c are obtained in the long (as compared to sizes of scatterers), short, and ultra‐short wavelength ranges. In the latter case the results can be obtained only when taking into account the spatial dispersion.
Application of Statistical Mechanics Using Asymmetric Electrolytes. Model Evaluation of Structural Properties of Ionic Gold—Cesium Melts
Authors: Rao R. V. Gopala , Satpathy A.
Published: July 2007

Treating the gold—cesium as an ionic melt around 50 at% of Cs, Blum's generalized equations of asymmetric electrolytes are used to compute the partial structure factors and the total structure factors. The partial and total pair correlation function and coordination numbers are calculated from the computed structure factors. It is found that the agreement between the calculated total structure factors and the experimental values is excellent. The value of the generalised Γ parameter is found to be similar to that of fused salts. The coordination numbers of like ions is much higher than the close packed value and is analogous to that found in fused salts. Further in the case of unlike ions the coordination number as in salt is less. It is very gratifying to note that the present method requires just two parameters namely the ionic diameters of gold and cesium.
Continuous Evolutions which Connect Quasilattices with Lattices
Authors: Torres M. , Pastor G. , Jiménez I. , Fayos J.
Published: July 2007

A newly modified projection method is developed in order to generate continuous transformations which connect quasilattices with lattices. The evolution and collapse of a 2D octagonal quasilattice, a continuous evolution of the 3D Penrose tiling which leads to a cubic primitive lattice on a side and to an f.c.c. vertices arrangement on the other side and, finally, the evolution and collapse of the historical 2D Penrose tiling are studied in detail. Applications of these quasiperiodic tiling evolutions to quasicrystal—crystal transitions and to atomic decorations of quasicrystalline phases are suggested.
Interatomic Forces and Pseudopotential Parameterization
Authors: Meyer A. , Young W. H.
Published: July 2007

It is shown that the calculated interatomic forces in a metal are sensitive to the pseudopotential postulated, even if the principal (“atomic”) node in the form factor is kept fixed. Much less sensitivity is displayed when the pseudopotential core is fixed with respect to low energy s‐ and p‐scattering.
Description of Interdiffusion Processes in Multicomponent Systems by the First Fick's Law
Authors: Slyusarenko E. M. , Soldatov V. S.
Published: July 2007

A new approach, based on Fick's first law, is proposed for the theoretical description of interdiffusion processes in multicomponent systems. In distinction to the well‐known model, where interdiffusion in an n‐component system is characterized by (n2 – n) partial (intrinsic) diffusion coefficients, in the model of independent fluxes n coefficients are used. To determine the analytical dependence of partial diffusion coefficients Di = Di(C1, C2, …︁, Cn) it is unnecessary to investigate the Kirkendall effect with the help of markers.
Kinetics of an Ensemble of Jogs on the Edge Dislocation for Inefficient Capture of Point Defects by Jogs
Authors: Borodin V. A. , Ryazanov A. I.
Published: July 2007

The kinetics of an ensemble of jogs on a straight edge dislocation is investigated for a material supersaturated with vacancies and interstitials. The concentration of jogs is determined in a selfconsistent manner under the assumption of low efficiency of absorption of point defects by dislocation jogs. The range of validity of the results obtained is discussed.
Particle Size Effects of Ion Crystallites
Authors: Fritsche H.‐G.
Published: July 2007

The cohesive energy of cubes (NaCl) N (4 ≦ N ≦ 500) is optimized, changing the uniformly assumed size‐dependent nearest‐neighbour ion pair distance, by means of summation of pair potetials. Formulae of particle size effects of energy‐dependent quantities – compressibility, surface energy, surface tension, pressure, and chemical potential – are derived analytically. Despite of the longrange order of the Coulomb interaction of ions, all the investigated size effects are dominated by the topology of the particles.
On Concentration Dependences of the Band Parameters in AIIBVI Solid Solutions with Structural Phase Transitions
Authors: Areshkin A. G. , Suslina L. G. , Fedorov D. L.
Published: July 2007

The connection between the structure of solid solution and its spectroscopic and band parameters is discussed on the example of ZnxCd1−xSe and Zn1−xMgxS systems with the structure phase transition: zinc blende (ZB)‐wurtzite (W). It is shown that if the Eg(x) dependence is parabolic for the ZB and W pure structure ranges, it is linear in the phase transition range (for the Zn1−xMgxS system). Eg(x) is always higher for the anisotropic crystals (with stacking faults (SF) and W) than for the ZB ones depending on the more ionic character of their chemical bond. The influence of the disorder potential due to composition x and SF concentration fluctuations on the exciton and band parameters of the solid solutions is considered.
Non‐Zero Momentum Pairing and Peierls Order in One‐Dimensional Systems
Authors: Fazakas A. B. , Pitis R.
Published: July 2007

A one dimensional solid of the kind which may undergo a Peierls transition is considered in the mean field approximation. The electrons in a half‐filled tight‐binding band interact via the soft or softening phonons. It is found that, for reasonable values of the interactions parameters, electron pairs with the momentum equal to that of the phonons condense at low temperatures, coexisting with the Peierls order. The transition temperatures are discussed.
The Conduction Band Parameters and Scattering Mechanisms in Solid Solutions Based on Bi2Te3
Authors: Kutasov V. A. , Lukyanova L. N.
Published: July 2007

Experimental weak‐field galvanomagnetic data are used to determine some conduction band parameters (the ratios of the effective mass tensor components mi/mj, the tilt angle of the principal axes of the constant energy ellipsoids, and the degeneracy parameter) using the many‐valley model of the band structure for n‐Bi2Te3 and its solid solutions. The charge carrier scattering mechanism is discussed. It is shown that the scattering parameter is not equal to −0.5, e.g. the value specifies for the acoustic scattering mechanism. The effective scattering parameter reff is calculated and its temperature and concentration dependences are found.
Critical Behaviour of n‐ZnSe Parameters in the Vicinity of the Metal—Insulator Transition
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

The critical behaviour of the parameters of n‐ZnSe is studied near the metal—insulator (M–I) transition obtained by variation of compensation degree or concentration of shallow donor impurity. It is found that the localization radius of the electron wave function, dielectric permittivity, density of states at the Fermi level as well as several other parameters characterizing the conductivity at the dielectric side of the transition are continuously varied over the critical region of the transition according to the scaling theory of localization. It is shown, that the critical concentration and critical indices for the M–I transition obtained by doping have somewhat lower values than that for the transition produced by compensation. The compensation smeares out the M–I transition and makes the concentration dependences of the system parameters in the critical region less abrupt. The symmetry of the M–I transition formed by doping is established as opposite to the slightly asymmetric transition induced by compensation. In the case of M–I transition obtained by doping replacement of electron localization on individual impurity centres by the Anderson localization is observed in the critical region while approaching the transition.
Piezomagnetoresistance Anisotropy of n‐Ge in Strong Magnetic Fields near the Metal–Insulator Transition
Authors: Matveev G. A. , Tsidilkovskii I. M. , Lonchakov A. T.
Published: July 2007

Over the temperature range 2 to 77 K longitudinal and transverse magnetoresistance (MR) measurements are performed on Ge:Sb crystals in magnetic fields up to 200 kOe. The crystals used are uniaxially compressed along the 〈111〉 axis and have electron concentrations between 0.82 × 1017 and 6.2 × 1017 cm−3. A large MR anisotropy is found to arise chiefly from the anisotropy of the energy gap between the Fermi level and the mobility edge. A correlation is shown to exist between the temperature dependences of the negative and positive MR's in high magnetic fields. From an analysis of the concentration and temperature dependences of the MR anisotropy, it is inferred that for n > nc there exist certain regions of electron concentrations and temperatures where, despite the metallic character of conduction, effects show up which are typical of impurity band charge carriers. Put another way, the electron states in these regions are intermediate between band states, for which the scattering is weak, and virtually localized states, for which the scattering is strong.
Electronic Degeneracies, Inelastic Processes, and Bohm‐Aharonov Magnetoresistance Oscillations in Ordered Normal‐Metal Rings
Authors: Dunne L. J.
Published: July 2007

A model is presented for magnetic flux dependent inelastic scattering processes in cyclic systems. This goes beyond previous work which assumes flux independent scattering processes. It is suggested that the model is of relevance to the interpretation of magnetoresistance oscillations which are observed in ordered normal metal rings. Electron scattering processes become more effective at flux values corresponding to degeneracies in the ring electronic states, and this manifests itself by oscillations in the magnetoresistance.
First‐Order Quantum Corrections to the Diffusivity and Current‐Induced Density Fluctuations in the Three‐Dimensional Bulk
Authors: Lenk R.
Published: July 2007

Employing a superposition representation of the density matrix for a fixed energy, the first order quantum corrections to the diffusivity are calculated for independent charge carriers scattered by uncorrelated point‐like scatterers. It is shown how fluctuations in carrier density, especially those which are caused by the current itself, contribute to the quantum corrections.
Electroreflectance Lineshape of Step‐Like Doped GaAs Structures
Authors: Goldhahn R. , Röppischer H.
Published: July 2007

For a semiconductor structure consisting of a homogeneously doped layer on a lower‐doped substrate of the same material the electroreflectance lineshape at the fundamental absorption edge is studied by model calculations. With the electric field penetrating into the substrate a characteristic superposition of the two partial spectra arising from the differently doped semiconductor regions is found. The change of the lineshape simulated for a GaAs structure in dependence on the modulation conditions and layer thickness is confirmed by electroreflectance measurements using successive layer removal. From the applied voltage producing first spectrum modification the thickness of the top layer can be estimated.
Raman Spectra of the Incommensurate and Ferroelectric Phases of Rb2CoCl4 Single Crystals
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Smutný F. , Vaněk P. , Březina B.
Published: July 2007

Raman spectra of Rb2CoCl4 (RCC) single crystals, prepared by an improved method, are studied at 90 to 297 K. The results show that the temperature dependence of the spectra of RCC is analogous to that of Rb2ZnCl4 and Rb2ZnBr4. Eigenfrequencies of internal modes v1 and v3 vary with temperature in a manner well describable by a model, which is suggested by Rasing et al. for Rb2ZnBr4. Low‐frequency lines at 20 and 37 cm−1 exhibit a pronounced temperature dependence. The broadness of spectral lines speaks for a high anharmonicity of oscillations in RCC.
The Stress Fields on Secondary Slip Systems Due to a Group of Dislocations in a Stress Gradient
Authors: Hu Xiaoyu , Margolin H.
Published: July 2007

Resolved shear stress distributions are calculated from the stress fields arising from screw and edge dislocation arrays produced by stress gradients. The resolved shear stress distributions are determined for planes parallel to a primary slip plane which has undergone slip and for other slip systems. For the screw dislocation array largest resolved shear stresses are found on the cross slip plane. For edge dislocation arrays largest resolved shear stresses are found on the conjugate slip system.
Volume Dependence of Short‐Range Force Constant and Dielectric Properties of Alkali Halides
Authors: Pachauri A. K. , Sharma A. K. , Saxena H. C.
Published: July 2007

A simple and useful empirical relationship showing the volume dependence of short‐range force constant is investigated. The relation is found to hold well for the variation from one crystal to the other as well as for a given crystal under changing volume. The usefulness of the relationship is demonstrated by calculating the volume derivatives of dielectric constant, and optic mode longitudinal and transverse Grüneisen parameters. The special feature of these calculations is that they do not require the detailed knowledge of the interionic potentials. The results obtained are found in good agreement with experimental data.
In Search of Hydrogen Local Vibrational Modes in CuCl, CuBr, CuI, ZnS, and AISb
Authors: Tatarkiewicz J. , Cardons M. , Breitschwerdt A. , Lin C.‐T. , Grötzschel R. , Witthuhn W.
Published: July 2007

A systematic study is made of hydrogen localized vibrational modes in some III–V, II–VI, and I–VII compounds after proton implantation. HCl vibrations are observed in CuCl with an energy of 2585 cm−1, but no CuH vibrations. This is verified by the lack of hydrogen‐related vibrations in CuBr and CuI. In ZnS vibrations of ZnH are observed at 1325 cm−1 and HS vibrations at 2415 cm−1. No hydrogen‐related vibrational modes are observed in AlSb after proton irradiation. For all hydrogen local vibrational modes the measured oscillator strengths are about 0.075. It is found that vibrational energy of HS agrees with that predicted from a simple diatomic molecular bond. ZnH vibrations exhibit much higher energies, and HCl much lower energies, than those calculated from the model. These results are discussed in terms of the ionicity of crystal bonds.
Raman Scattering in Gallium Selenide and Sulfide Films
Authors: Ibragimov T. D. , Kurbanova G. G. , Gorelik V. S.
Published: July 2007

The spectra of Raman scattering (RS) in gallium selenide and sulfide films are investigated. The variation in the intensity of RS peaks with the film thickness is shown to be fairly well described by the theory of light scattering in an absorbing medium. A deviation from this theory is observed at the peak corresponding to the RS‐forbidden A mode of GaSe. It is explained by the contribution of the surface vibrational states to the RS cross‐section at this peak.
Dynamic and Electrooptic Parameters of Monolayers in Ethane Adsorbed on Graphite
Authors: Podoprigora V. G. , Remizov I. A. , Shabanov V. F. , Shmeleva L. V.
Published: July 2007

The vibration spectrum of surface phonons for ordered phases of ethane monolayers adsorbed on graphite is investigated using different potential functions. The average heat motion amplitudes of molecules adlayer, effective molecular polarizabilities, and their derivatives with respect to external coordinates, which determine Raman spectra intensities as well as the section of one‐phonon inelastic neutron scattering from the surface are calculated taking into account the ethane‐substrate dynamic interaction. The last results are compared with experimental ones.
Absence of the Gap in the Optical Excitation Spectrum of TCNQ Salts with Methyl Derivatives of Pyridinium
Authors: Vainrub A. M. , Zavt G. S. , Graja A.
Published: July 2007

It is shown that the dispersion of the real and imaginary parts of the dielectric function of the TCNQ salts with methyl derivatives of pyridinium gives important information about the density of electronic states. It leads to the conclusion that a gap is not present in the optical excitation spectrum of the salts. It is shown that the model of the localized charge oscillations in dimers is inadequate for the salts.
Phase Transition and Padé Approximants for Fröhlich Polarons
Authors: Selyugin O. V. , Smondyrev M. A.
Published: July 2007

To extrapolate the weak‐ and the strong‐coupling expansions into the intermediate‐coupling regime two‐point nondiagonal Padé approximants are used. It is observed that there exist two alternative versions of approximants, leading to upper and lower bounds whose properties differ from those proven for Stieltjes series. Taking the Feynman polaron as an example, its characteristics are calculated in higher orders of the weak‐ and the strong‐coupling expansions and the corresponding Padé approximants are constructed. This makes possible to tighten the gap between the bounds considerably. Applying the method to the actual Fröhlich polaron the exact result are used of three‐loops calculations of its ground state energy (E3 = −0.806070048 × 10−3). The polaron characteristics seem to lie between smooth functions of the coupling constant — the fact that restricts their hypothetic jumps. This indicates the absence of a phase transition at least in those numerical limits where it is suspected to exist.
Reentrant Paramagnetic‐AFM Paramagnetic Phase Transitions in La2CuO4 Theory
Authors: Hudák O.
Published: July 2007

Statistical thermodynamic mean‐field theory for 3d AFM ordering in La2CuO4‐δ is presented. Conditions for its existence, reentrant phenomena, effective reduction of magnetic moments, density temperature dependence of magnetic singlets, and isolated 1/2‐spins are the main theoretical results. Their correspondence with experimental results is discussed.
On the Thermodynamical‐Statistical Consistency of a Variational Approximation for the Free Energy
Authors: Ferreira J. R. Faleiro
Published: July 2007

An upper bound for the free energy is found which is more general than the Bogolyubov inequality. It generates an approximation which can accurately preserve the consistency between thermodynamic and statistical mechanics definitions.
Z2‐Oscillations of the Proton Stopping Maximum in Gases and Solids
Authors: Balashova L. L. , Chumanova O. V. , Kabachnik N. M.
Published: July 2007

The local electron density approximation is used to calculate the position and value of the maximum in the proton stopping cross‐section for gases and solids. The electron density of atoms in gases is calculated using the Hartree‐Fock‐Slater approximation. The electron density of solids is represented by a muffin‐tin model. The calculations show significant variations in the position of the stopping maximum as a function of Z2 and demonstrate a substantial difference in the Z2‐dependences for gases and solids. The calculation results are in qualitative agreement with experimental data.