bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model for the Calculation of Monovacancy and Divacancy Contributions to the Impurity Diffusion in Noble Metals
Authors: Neumann G.
Published: July 2007

On the basis of an earlier proposed model (Neumann and Hirschwald 1973, 1974) the impurity diffusion in noble metals is described by additionally taking into account the contribution of divacancies. The influence of the divacancy contribution on the effective diffusion energy and on the temperature dependence of the isotope effect is discussed. The divacancy contribution causes a curvature of the Arrhenius plot of the diffusion coefficient. For fast diffusing impurities the temperature behaviour of the correlation factor f leads to a distinct decrease of this curvature. A further consequence of the temperature behaviour of f for fast diffusers is that the low‐temperature value of ΔQ, the difference between the activation energies of impurity diffusion and self‐diffusion, represents an acceptable upper limit for the binding energy between impurity and vacancy.
The Magnetic Phase Transition in Amorphous and Disordered Crystalline Ferromagnets
Authors: Kellner W.‐U. , Fähnle M. , Kronmüller H. , Kaul S. N.
Published: July 2007

The magnetic phase transition of amorphous FeNi‐base alloys and disordered crystalline FeNi alloys is investigated, and the methods for a determination of the asymptotic critical exponents and the effective exponents are discussed critically. Two general results are obtained: 1) For the asymptotic exponents no significant deviations from the 3d‐Heisenberg exponents are found. 2) For the effective susceptibility exponent γ(T) the characteristic non‐monotonic temperature dependence is observed as predicted by the correlated molecular field theory.
Phase Transitions in Ordered and Disordered Ferrimagnets. II. Experimental Results
Authors: Haug M. , Fähnle M. , Kronmüller H. , Haberey F.
Published: July 2007

The magnetic phase transition is investigated by a vibration magnetometer for the homogeneous ferrimagnet Fe3O4 and the structurally disordered ferrites ZnxNi1−xFe2O4 with x = 0, 0.25, 0.5, and 0.75. For both ordered and disordered ferrimagnets the asymptotic critical exponents are compatible with the ones of a homogeneous 3d‐Heisenberg ferromagnet. Outside the asymptotic critical regime there is a strong effect of the structural inhomogeneities on the thermodynamic behaviour. In close analogy to the case of disordered ferromagnets, the effective Kouvel‐Fisher exponent γ(T) first increases with increasing temperature T for disordered systems, as predicted by the correlated molecular field theory and by Monte Carlo computer simulations, whereas it initially decreases for a homogeneous ferrimagnet. Anomalies in the modified Arrott plots at low fields are discussed.
The Influence of the Size Quantization on the Fermi Energy and the Effective Mass in Bi Films
Authors: Zaluzny M. , Lukasik A.
Published: July 2007

The influence of the size‐quantization on the Fermi energy, the carrier density, and the cyclotron effective mass in Bi films with normal along the trigonal, binary, or bisectrix axes is discussed. The numerical calculations are performed in the framework of the two‐band ellipsoidal model. Comparison with the results obtained in the framework of the ellipsoidal parabolic model is given.
Low‐Temperature Magnetoresistance in Medium‐Angle Grain Boundaries in Germanium
Authors: Xia Yi‐Ben , Bangert E. , Landwehr G.
Published: July 2007

Magneto‐transport properties of grain boundaries in germanium bicrystals are studied in the liquid helium temperature range. For samples with 7° and 8° tilt angle an exponential magnetic field dependence is observed, which is analyzed in terms of two‐dimensional hopping conduction. The acceptor concentration N in the grain boundary can be deduced by comparing different magnetic field orientations. A surprising temperature dependence of N is obtained. In addition, the activation energy is determined as about 0.5 meV, typical for the hopping process, and decreases slightly with increasing magnetic field.
Three‐Branch Excitonic Polaritons in Direct Band Gap Cubic Semiconductors
Authors: Khamsasy Ch. , Van Hieu Nguyen , Viet Nguyen Ai
Published: July 2007

The transition is studied between a photon and “heavy” and “light” excitons in direct‐band gap cubic semiconductors with a fourfold degenerated highest valence band at the center of the Brillouin zone. The transition matrix elements are calculated in the second‐order approximation of the perturbation series with respect to a small constant proportional to the difference of the mass of the heavy and light holes. The algebraic equation determining the dispersion of the three‐branch polaritons is derived. The spin structure of the wave functions of the corresponding excitons is established.
Integro‐Differential Equations for the Evolution in the Athermal Pre‐Electron–Hole Plasma State of an Irradiated Direct Semiconductor
Authors: Heiner E.
Published: July 2007

A consistent extended TDHF theory is treated for the description of electron motion of a laser irradiated direct semiconductor. Dissipation and memory is involved, therefore the theory is applicable in the athermal pre‐electron–hole plasma state of evolution. As a result the integro‐differential equations are derived which are the evolution equations for diagonal and off‐diagonal expectation values.
Multipole Theory of the Polarization of Solids by Point Defects. IV. Electronic and Spatial Structure of Single Electronic and Hole Centers and Their Pairs in LiF, KCl Crystals
Authors: Kantorovich L. N.
Published: July 2007

A method proposed previously for calculating the electronic and spatial structure of neutral and charged point defects in ionic crystals with self‐consistent incorporation of the polarization effects into the eigenvalue spectrum is applied to the calculation of characteristics of concrete single electronic (F2, F, F) and hole (H, Vk, V2) centers and their pairs ({F, Vk}, {F, H}) in LiF, KCl crystals. The necessity of self‐consistent evaluation of polarization, as well as the dependence of calculation results on approximations used in simulating uncompensated charge density in defective region are discussed. Approximations based on point and non‐point polarizable charges (simulators) are compared. The electronic structure of defects is calculated on the basis of the INDO semiempirical method.
The Impact‐Parameter Dependence of Electron Stopping in Proton Collisions with Gas and Solid Atoms
Authors: Kabachnik N. M. , Kondratev V. N. , Chumanova O. V.
Published: July 2007

The semiclassical approximation with rectilinear trajectory is used to calculate the impact‐parameter dependence of electronic stopping for fast‐proton collisions with gas and solid atoms. The effects arosen from electron shell rearrangement and dynamic screening of proton charge in a solid, on the electron stopping are studied for case of solid targets. The calculation results are compared with experimental data and with approximate calculations based on sum rules and local electron density approximation.
Lattice Vibrations of CuGaSe2, CuInSe2 Ternary Compounds, and CuGaxIn1−xSe2 Solid Solutions
Authors: Bodnar I. V. , Smirnova G. F. , Smirnova T. V. , Aleshchenko Yu. A. , Vodopyanov L. K.
Published: July 2007

On the basis of IR reflection, transmission, and Raman spectra the frequencies of the vibrational modes of CuGaSe2, CuInSe2, and CuGaxIn1−xSe2 are obtained and identified. It is shown that the lattice vibrations of the solid solutions display mixed type behaviour. In the frequency range ω > 200 cm−1 the vibrational modes show two‐mode behaviour. Two relatively independent bands in this range are due to vibrations of GaSe atoms and InSe, respectively, in antiphase. The vibrational modes in the low frequency region (ω < 200 cm−1) display one‐mode behaviour.
Raman Scattering at the CaF2 Crystal Surface Excited by an Evanescent Optical Wave Field
Authors: Sheng Y. Q. , Recknagel E. , Weidinger A. , Gu Z. G. , Lai Z. Y. , Zhuang Z. C.
Published: July 2007

New results are given of Raman scattering measurements on the dispersion characteristics of surface‐phonon polaritons at the air—CaF2 interface using the Otto configuration. A phenomenological description of the dispersion relation is also given theoretically as well. The experimental results are in good agreement with the theory. For comparison, the dispersion curve of the surface‐phonon polariton under the same configuration is also measured by the ATR method in the in fared region and the agreement of the results from both the methods is also satisfactory.
Two‐Dimensional Electron Pair in a Transverse Magnetic Field
Authors: Goroshchenko S. Ya. , Ukrainskii I. I.
Published: July 2007

The effect of electron—electron interaction on the quantization of the motion of two‐dimensional electron pair in a transverse magnetic field is studied. It is shown that the energy spectrum of inner motion of the system is not degenerate when the magnetic field strength exceeds a certain value. Decreasing the field strength below this value a variety of level crossings is obtained. In the field region with a nondegenerate spectrum there exists a significant overlap of pair wave functions with those for the case of noninteracting electrons.
Characteristic Features of the Electronic Structure of Carbon Films
Authors: Gavrilenko V. I. , Klyui N. I. , Litovchenko V. G. , Strelnitskii V. E.
Published: July 2007

Studies of the electroreflectance spectra of microcrystalline carbon films make it possible to reveal two energy gaps E1 and E2 within the spectral range from 1.0 to 5.6 eV. Using the strong‐bond method, a model of the electronic energy structure (EES) of microcrystalline carbon is developed explaining the emergence of semiconductor properties of this material and describing the available experimental data. An analysis of the data published in literature and of those obtained during these investigations allows to specify, within the limits of the model mentioned, additional features in the changes of the electronic structure of carbon by structural disordering. Characteristic features of the EES of hydrogenated carbon films are studied and substantial difference between the EES of a‐C:H and a‐C is shown.
Transition Probability of Impact Ionization by Holes in Silicon
Authors: Gautam D. K. , Khokle W. S. , Garg K. B.
Published: July 2007

An analytical expression is developed for the transition probability per unit time for impact ionization by holes. The approach is based upon time dependent perturbation calculations and the Bloch functions for the states of electrons and holes. The threshold energy of ionization by holes is calculated for the valley L1 for the electron band structure of silicon. The results obtained for the probability are in good agreement with experimental results for threshold energy and theoretical results for the ionization probability.
Calculation of Electrical Resistivity of Some Liquid Metals by the Mode‐Coupling Method
Authors: Jha D. N.
Published: July 2007

The resistivities and temperature coefficients of resistivity (TCR) of some liquid metals (Ag, Au, Fe, Ni, Eu) are calculated by the mode‐coupling approximation method of Götze and compared with respective experimental values. Good agreement is found for some of them. The sign of TCR is closely related to the variations in the values of the electron‐phonon coupling parameter.
On the Luminescence of CaO:Sn2+
Authors: Donker H. , Smit W. M. A. , Blasse G.
Published: July 2007

The luminescence spectra and decay times of CaO:Sn2+ are studied in the temperature range between 4.2 and 295 K. The emission spectra show one emission band with a maximum at 490 nm at 4.2 K. In the diffuse reflection spectra and the luminescence excitation spectra the A, B, and C bands are observed at 365, 324, and 294 nm, respectively. CaO:Sn2+ shows a very long after‐glow when excited at room temperature. The observed temperature dependence of the decay time may be fitted to a three level scheme leading to the parameter values τ0 = 350 μs, τ1 = 0.7 μs, and ΔE = 43 cm−1. A comparison is made with the luminescence of Sn2+ and Pb2+ in other calcium chalcogenides.
EXAFS in ZnxCd1−xGa2S4 Defect Chalcopyrite Solid Solution
Authors: Lottici P. P. , Antonioli G. , Razzetti C.
Published: July 2007

The structure of the nearest neighbours environment in the mixed defect chalcopyrite ZnxCd1−xGa2S4 is investigated by the EXAFS (extended X‐ray absorption fine structure) spectroscopy at the Zn and Ga K‐edges. The bond distances in the end member crystals and for different compositions in the alloy are determined. In addition to a conversation of the tetrahedral bond lengths with composition, the EXAFS analysis suggests an internal distortion in the ZnGa2S4 compound, in contradiction with literature data.
Collective Action Formalism on the Keldysh Contour for Disordered and Hubbard‐Correlated Electrons
Authors: Kolley E. , Kolley W.
Published: July 2007

A real‐time finite‐temperature field theory on the Keldysh contour is used to describe the dynamics of an electron system within a random Hubbard model. The effective, i.e. quenched‐averaged, fermionic action under the functional integral is bosonized by introducing both a matrix field and an exchange field via Hubbard‐Stratonovich transformations. The resulting collective action permits the loop expansion, giving rise to a systematic approximation scheme. The saddle point and Gaussian fluctuations around it are calculated.
Approximate Calculation of Inner‐Shell Binding Energies and Auger Transition Energies of Solid Silicon Compounds
Authors: Zwanziger C. , Petrowa S. , Reinhold J. , Streubel P. , Meisel A.
Published: July 2007

Up to now the extended Fenske‐Hall LCAO method (EFH method) has been used to calculate approximately the inner‐shell binding energies and their chemical shifts for a variety of inorganic and organic molecules. In this paper the first attempt is made to test the EFH method for solids. First results are given for silicon and some of its compounds (SiC, Si3N4, SiO2, Na2SiF6). The solids are modeled by clusters saturated by hydrogen‐type pseudoatoms. For these clusters the inner‐shell binding energies Si 1s and Si 2p as well as the Auger energies KLL are calculated. A reasonably good agreement of the calculated chemical shifts of the 1s, 2p, and KLL energies with experimental data of the solid surfaces can be noted. Furthermore, one can predict the order of magnitude of the relaxation energies.
Galvanomagnetic Properties of p‐Hg1−xCdxTe
Authors: Höschl P. , Moravec P. , Prosser V. , Szöcs V. , Grill R.
Published: July 2007

A three‐level model for one divalent acceptor (Hg vacancy) and one monovalent acceptor (foreign atom) is suggested. The hole mobility is determined for p‐like wave functions (polar phonons and ionized impurities). Low temperature (10 to 300 K) galvanomagnetic measurements of undoped p‐Hg1−xCdxTe (x ≈ 0.2) are reported. A simultaneous analysis of the hole concentration and Hall mobility data in the region 10 to 100 K and Hall coefficient and conductivity data in the region 100 to 300 K yield ionization energies of ≈ 6 meV and ≈ 0.7 Eg (energy gap) for the Hg vacancy and ≈ 12 meV for the foreign acceptor. In the temperature region 100 to 300 K the mobility of electrons is determined, too.
NMR Study of the Zinc Chalcogenides (ZnX, X = O, S, Se, Te)
Authors: Bastow T. J. , Stuart S. N.
Published: July 2007

A nuclear magnetic resonance investigation of the solid zinc chalcogenides ZnX (X = O, S, Se, Te) is carried out, using the following nuclei as probes, 67Zn, 17O, 33S, 77Se, and 125Te. The spectra yield nuclear quadrupole coupling constants and chemical‐shift parameters for polycrystalline ZnO and Zns in the wurtzite (hexagonal) form, and chemical shifts and linewidths for polycrystalline ZnS, ZnSe, and ZnTe in the sphalerite (cubic) form. A single crystal of ZnO is used to obtain an accurate measurement of the quadrupole coupling constant for 67Zn, ∣e2qQ/h∣ = 2.4065(15) MHz at 296 K, in agreement with a recent Mössbauer‐effect measurement. The electric field gradient of the wurtzite structures is analysed with a simple ionic model, and the results are found to be in semi‐quantitative agreement with experiment.
Linear Birefringence Investigations of the Jahn‐Teller Distorted Phase in the Mixed Crystal Systems (Tbx, Tm1−x)VO4 and (Tbx, Yb1−x)VO4
Authors: Pilawa B. , Hess G. , Kahle H. G. , Kasten A.
Published: July 2007

Measurements of the linear birefringence in the distorted phase of (Tb, Tm)VO4 and (Tb, Yb)VO4 crystals allow to separately establish the contributions of the individual rare‐earth ions and the anion complex for the first time. By this, the dissimilar wavelength dependence of the birefringence in pure Tb and Tm vanadate can be understood. A mean field theory including random‐strain effects is used to treat the distorted phase and to elucidate the absence of the Jahn‐Teller phase transition at low Tb concentrations.
Positron Annihilation Studies in Zeolites
Authors: Dębowska M. , Abbé J. Ch. , Duplâtre G.
Published: July 2007

Positron annihilation experiments using both lifetime spectroscopy and Doppler broadening of the annihilation lineshape technique are performed for various pure zeolites and for mordenite impregnated with highly dispersed gold particles. Changes in the annihilation parameters are tentatively correlated with the properties of the samples and, in case of impregnated samples, attributed to the presence of gold particles in the matrix of the zeolite.
Influence of a vVacancy on Luminescence of Pb+ Centres in Alkali Halides
Authors: Nagli L. E. , Dyachenko S. V.
Published: July 2007

Luminescence of Pb+ centres in X‐irradiated Pb2+ doped KCl, KBr, and KI crystals is first observed at 1.29, 1.21, and 1.14 eV, respectively. It is excited in the bands of KCl:Pb2+ at 4.93, 4.45, 3.70, 2.03 eV, of KBr:Pb2+ at 5.20, 4.55, 4.20, 3.20, and at 5.10, 4.30, 3.91, 3.52, 3.02, eV for KI:Pb2+. The effect is studied of the presence of the cation vacancy on both, the excitation and emission spectra of the Pb+ centre. Temperature, kinetic, and polarization characteristics of Pb+ and Pb+vc−‐centres in KCl:Pb2+ are investigated.
Picosecond Transient Optical Nonlinearities in CdS and CdSSe
Authors: Egorov V. D. , Flögel P. , Nguyen Hoang Xuan , Kaschke M.
Published: July 2007

Nonlinear absorption of CdS and CdS0.7Se0.3 crystals is studied around room temperature using an excite‐and‐probe technique in the ps time region and taking Fabry‐Perot interferences into account. Large nonlinear changes of the optical coefficients are obtained. The experimental spectra are in reasonable agreement with the theoretical ones assuming a heating of the excited carriers. The nonlinearities relax within about 1 ns.
A New Empirical Two‐Body Interaction Potential Fitted to Second‐ and Third‐Order Elastic Moduli
Authors: de Graff M. , Delaey L.
Published: July 2007

A new empirical model for an interatomic pair potential is derived, allowing for a full fit of second‐and third‐order elastic moduli. First the general equations, valid for any crystal class, are derived. These equations are then applied to the body centered cubic and the face centered cubic structures; the potential derivatives are then expressed as linear combinations of the elastic moduli. Introducing a number of free parameters (e.g. potential depth, core slope,…) the potential can be constructed as a set of fourth order piecewise continuous splines. Some examples are also given to illustrate the effect of changes in the fitting parameters. Finally the applicability of the new model is briefly discussed.
Thermodynamics of Defect Formation and Defect Interaction in Compound Semiconductors
Authors: Bulyarskii S. V. , Oleinikov V. P.
Published: July 2007

Based on the Gibbs cannonical distribution, a number of physical quantities is related to crystal growing conditions such as various point defect densities (intrinsic, vacancies, antistructural, complex of some point defects), high‐temperature density of free carriers, homogeneity region width, and impurity distribution factor. It is discussed how to calculate the Gibbs partial potential from experimental data. The results can be now used for solving a variety of problems of point defects in semiconductors including effects of complex formation.
Phonon–Phonon Interaction in Gadolinium–Gallium Garnet Crystals
Authors: Kleszczewski Z. , Bodzenta J.
Published: July 2007

Propagation velocity and temperature dependence of the sound wave attentuation coefficient in gadolinium–gallium garnet crystals are measured. The measurements are carried out in the frequency range 0.4 to 2.0 GHz and temperature range 77 to 293 K. On the basis of the measurements Debye temperature, specific heat of crystal as a function of temperature, and the temperature dependence of thermal phonon lifetime are determined. For calculation it is assumed that the examined material is isotropic.
Non‐Linear Light Absorption Spectroscopy in Sb–S–I Crystals and Glasses
Authors: Lisitsa M. P. , Turyanitsa I. D. , Fekeshgazi I. V.
Published: July 2007

The spectral dependence of the two‐photon induced linear light absorption in Sb–S–I crystals and glasses are studied. An allowed–forbidden character of the two‐photon transitions and the spectral pecularities due to two‐step transitions through real energetic levels are found.
Thermoluminescence and Fluorescence Studies on RbBr:Gd2+
Authors: Sastry S. B. S. , Muralidharan G.
Published: July 2007

TL glow of γ‐irradiated crystals shows a single peak at 380 K. On F‐light bleaching a new peak attributable to Z1‐centres appears around 355 K. The presence of OH− reduces the TL glow. The characteristic emission of the impurity is observed at 3.65 eV. The irradiated crystals show the presence of the “O2−–vacancy” complex. The TL process is due to the thermal release of F‐electrons.
Analysis of Crystal Binding and Thermoelastic Properties of Cuprous Halides, Silver Halides, and Thallous Halides
Authors: Chaturvedi S. D. , Dixit R. C. , Sangachin A. A. S.
Published: July 2007

Crystals of cuprous halides, silver halides, and thallous halides are found to show significantly different behaviour from that of alkali halides. This difference is mainly due to the presence of outermost d‐electrons present in Cu+, Ag+, and Tl+ ions. In the present paper an analytical potential form is used for the overlap repulsive energy derived by Harrison from quantum mechanical considerations. The parameters in this potential form have direct correlation with the valence state energies for outermost d‐electrons. The potential model is applied to calculate the cohesive energies, pressure derivatives of bulk modulus, Grüneisen parameter and its volume dependence using different existing theories.
Image Potentials and Image Forces in the Polaron Theory
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M.
Published: July 2007

A polaronic approach for the problem of image force potential is developed. Within this approach dispersion of the dielectric constant and electron recoil effects are taken into account. For the semiconductor‐vacuum interface at small values of electron effective mass and high values of semiconductor dielectric constant the electron recoil is found to cause a greater reduction of the potential than the dispersion of dielectric constant, and to play the main role in cutting off the singularities of the image force potential. Analytic formulae for the image force potential energy are obtained accounting for the electron recoil effects and ignoring the dispersion. The coordinate dependences of this potential in vacuum and in medium are analyzed.
Excitonic Processes and Thermoluminescence in NaCl Crystals Doped with Mg or Mn
Authors: Egranov A. V. , Nepomnyachikh A. I.
Published: July 2007

Processes of defect creation by VUV‐excitation are studied by the thermoluminescence method. NaCl crystals doped with Mg or Mn are irradiated at 80 K by monochromatic VUV‐light in the region of 7 to 8 eV. Excitation spectra of the glow peaks at 195 K (NaCl‐Mg) and 220 K (NaCl‐Mn) have maxima at 7.5 and 7.4 eV, respectively. It is concluded that the TL excitation spectra correspond to the formation of an exciton near the divalent metal (Mg2+ or Mn2+) of the impurityvacancy complex. The decay of these excitons leads to formation α‐Iz pairs at 80 K.
On a Theory of the Electronic Spectrum and Magnetic Properties of High‐Tc Superconductors
Authors: Gaididei Yu. B. , Loktev V. M.
Published: July 2007

An attempt is made to derive consistently the Hamiltonian of electron excitations of high‐Tc superconductors (HTSC) proceeding from their ionic and crystal structure. The carriers are shown to be able to move both, over the copper and oxygen subsystems. The spectrum of free (excess) carriers is found. It is established that the Jahn‐Teller (two‐level) character of Cu2+ results in a specific pairing mechanism being the most effective in rhombically distorted lattices. The analogy between HTSC and Kondo lattices (or in some sense heavy‐fermion systems) is traced and the possible reason of suppressing magnetism and breaking the magnetic order in HTSC is discussed.
Er2O2SO4 — An Ising System with Six Magnetic Phases
Authors: Mayr A. , Paul W. , Kahle H. G.
Published: July 2007

At low temperatures, Er2O2SO4 orders as an Ising antiferromagnet with moments along the crystallographic c‐axis. Measurements of the magnetisation in zero magnetic field show two anomalies at T N1 = 1.58 K and TN2 = 1.54 K, indicating two different ordered phases. In external fields applied along the easy axis, three ferrimagnetic phases with fractions 1/4, 1/3, and 1/2 of the saturation magnetisation are traversed before the saturated paramagnetic state is reached. The spin structures of the different phases are discussed on the basis of topological considerations developed by Kanamori.
A Global Cut‐and‐Project Method to Construct Generalized Fibonacci Lattices and Quasilattices
Authors: You J. Q. , Hu T. B.
Published: July 2007

A global cut‐and‐project method is developed. By this technique, the construction is discussed of aperiodic lattices including both, generalized Fibonacci lattices and octagonal, decagonal, and dodecagonal quasilattices. Diffraction patterns with 8‐, 10‐, and 12‐fold symmetries are simulated, which agree well with the experimental results. A modulation is introduced to explain the two alternating sets of periodic layers along the 10‐fold axis in the diffraction pattern of decagonal quasicrystal.
Relations between Structure, Bonding, and Nature of Point Defects in Layered Crystals of Tetradymite Structure
Authors: Horák J. , Starý Z. , Klikorka J.
Published: July 2007

A quantum chemical calculation of bonding parameters in Sb2Te3, Bi2Te3, Bi2−xInxTe3, and Bi2Te3−xSx single crystals is carried out. The electric conductivity σ ⟂ c and Hall constant RH(B ∥︁ c) of the crystals in the Bi2Tes−xSx system are measured. These results present a basis for the discussion of the different role of impurities in anion and cation sublattices with respect to the bonding parameters and the concentration of anti‐site defects in the Bi2Te3−xSx system is calculated and compared with the formation energy of the same defects in the Bi2−xInxTe3 system.
Etude de l'évolution avec la température des modes actifs en diffusion Raman du ZnF2
Authors: Giordano J. , Sauvajol J. L.
Published: July 2007

Les évolutions de fréquences et des largeurs des modes actifs en diffusion Raman du fluorure de zinc ont été mesurées entre 4,2 et 300 K. Les contributions au glissement en fréquence liées à la dilatation volumique et à l'anharmonicité ont été évaluées pour chaque mode Raman. II a été misen évidence un amollissement du mode B1g avec la température. L'utilisation d'un modèle à ions rigides permet de relier l'évolution en température des constantes élastique du ZnF2 aux évolutions des fréquences Raman. Tous les résultats obtenus en utilisant différentes techniques expérimentales (Raman, IR, mesures de constantes élastiques) permettent d'envisager la tendance à la mise en place d'un ordre ferroélectrique à basse température. Nos résultats sont discutés et comparés avec ceux obtenus dans le cas de certains fluorures et oxydes métalliques de měme structure que ZnF2.
Positronium at Metal Surfaces
Authors: Shrivastava S. B. , Gupta V. K. , Bhadoriya K. S.
Published: July 2007

Based upon rate equation approach and considering the positron trapping in image potential a semiquantitative model is proposed to obtain the fraction of positronium formation at metal surfaces. Ps fractions are calculated for the surfaces of Cu(100), Ag(100), and Ag(111) and are compared with the experimental results. The results in Cu(100) and Ag(100) are in good agreement with the experiments, however, in case of Ag(111) these are underestimated at low temperatures.
Calculated Fermi Surface Characteristics of the Noble Metals
Authors: Graefenstein J. , Mertig I. , Mrosan E. , Antonov V. N. , Antonov Vl. N.
Published: July 2007

Some Fermi surface characteristics are calculated like the optical mass, the cyclotron masses, and the Fermi velocities of the noble metals. The underlying selfconsistent energy bands are obtained by means of a nonrelativistic KKR method for Cu and Ag and by means of a relativistic LMTO method for Au. The estimated optical masses agree satisfactorily with data from optical experiments. Taking into account the electron–phonon renormalization of the experimental data, the calculated cyclotron masses and anisotropic Fermi velocities agree well with de Haas‐van Alphen and magnetic field induced surface state resonance results. From the comparison of the theoretically and experimentally derived Fermi velocities the anisotropy of the electron‐phonon enhancement factor λ(k) is determined for Cu and Au.
About the F Center in Cesium Halides
Authors: Ruiz‐Mejía C.
Published: July 2007

The energy levels for the F center in cesium halides are determined. The point ion method and the ion size correction are applied. Vacancy‐centered trial wave functions of three types are used. The structure of NaCl and the CsCl are considered in the calculations. It is concluded that some investigations probably used the NaCl structure in their calculations for cesium halides. For wave functions of the Gourary‐Adrian type it is found that the Bartram et al. method can not be applied for values of the empirical parameter α ≧ 0.53. Others papers are discussed.
Deviations from Matthiessen's Rule in Ag;Au Alloys
Authors: Tiwari M. D. , Thummes G. , Kukermann V.
Published: July 2007

An experimental and theoretical study is made of electrical transport in dilute Ag‐based alloys with the view to understand the observed deviations from Matthiessen's rule. Various concentrations of gold are doped in silver. The measurements are extended to higher temperatures. A scattering‐time solution to the Boltzmann transport equation is employed. The anisotropy in the scattering is fully accounted for since it is known to be an important mechanism for deviations from Matthiessen's rule. Also included are the dynamical nature of the impurity, the interference between the impurity and the perfect‐crystal scattering, and the effects of mass‐change and force‐constant‐changes. Further, the role of the Debye‐Waller factor is discussed.
Thermal Expansion, Heat of Fusion, and Electron Density of Monovalent Metals
Authors: Mimkes J.
Published: July 2007

The enthalpy of monovalent metals is calculated as a function of electron density according to the model of nearly free electrons. The coefficient of thermal expansion of solid and liquid monovalent metals is given by heat capacity and Fermi energy, αP(T) = 2.5 × CP(T)/ϵF(T). The heat of fusion is determined by Fermi energy and relative change in volume at the melting point, Lm = 0.4ϵF(Tm) × (VL − VS)/VL. The agreement with experimental data is quite satisfactory for all alkali and noble metals.
Finite Motion of Microparticles in Tunnel‐Effect Multiquantum Well Structures
Authors: Volkov R. A. , Chuiko A. F.
Published: July 2007

A perturbation theory is developed for calculating eigenenergies (EE) and wave functions (WF) of a microparticle localized in a multiquantum well (MQW) semiconductor structure. Elastic tunnellings of one charge carrier and many charge carriers between quantum wells (QW) of arbitrary smooth shape are investigated. It is concluded that non‐decaying periodic currents can arise in the above structure. Analytical expressions are obtained for such currents and for times of tunnelling across the barriers of a set of QWs. Many‐particle tunnellings in a sawtooth double‐QW structure are considered.
Effect of a Tilted Magnetic Field on the Size‐Quantized Levels of Quantum Wells in Ultrathin Films of Narrow‐Gap Semiconductors
Authors: Bose M. K. , Majumdar C. , Maity A. B. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of a tilted magnetic field on the size‐quantized levels of quantum wells in ultrathin films of narrow‐gap semiconductors, taking n‐type InSb as an example. It is found that, in general, the energy eigenvalue of the lowest magneto‐size‐quantized level increases with increasing magnetic field and decreases both, with increasing film thickness and with increasing orientation of the magnetic field, for given values of the other parameters. Besides, it is observed that the difference of the energy eigenvalues of the lowest two magnetic sub‐levels of the lowest electric sub‐band reaches a maximum at a given magnetic field, showing a decrease with its orientation, while it increases with the film thickness.
Electronic Structure of Pd1−xNix Alloys Investigated by Positron Annihilation
Authors: Dębowska E. , Rudzińska‐Girulska J.
Published: July 2007

The entire concentration range of α‐phase Pd1−xNix alloys is studied by angular correlation and positron lifetime methods. The electron number per one alloy atom is analyzed and the progressive delocalization of d‐like electrons with increasing Ni concentration is postulated. Attention is also paid to the problem of annihilation rate in alloys. The changes in the character of annihilation parameter dependences on x are seemed to be connected with para‐ to ferromagnetic transition.
Dynamics in the System of Dipolar Impurity Centers in Crystals
Authors: Bersuker G. I.
Published: July 2007

A model is proposed for the description of the dynamics in the system of dipolar impurities in crystals. The impurities are assumed to reorient by the Arrhenius temperature dependence in the case when the activation energy is much larger than the temperature of reorientation freezing (the temperature of the phase transition in the impurity subsystem). The reorientation is caused by the transitions between the localized (in the minima of the adiabatic potential) and excited delocalized states of the impurity induced by one‐phonon processes (the multiphonon ones are ineffective at the low temperatures under consideration). The freezing of the reorientation at each center takes place at temperatures, at which the energy gap between the effectively populated localized state and the delocalized one becomes larger than the maximum frequency of the crystalline phonons. The rise of the impurity concentration increases the phonon‐exchange interaction between the near‐neighbor centers during their reorientation, resulting in the increase of the energy of the delocalized state, and hence in the increase of the freezing temperature of the dipole dynamics. In the framework of this approach the system of Li+:KTaO3, is considered as an example.
Theory of Superconductors with Strong Coupling in the Bogolyubov Method
Authors: Lozovsky V. Z. , Nazarenko A. B. , Khudik B. I.
Published: July 2007

The Bogolyubov U–V transformation method is generalized to the diagonalization of an electron–phonon Hamiltonian in the superconducting medium. The self‐consistent equations are written. The structure of the quasi‐particle spectrum is found. The criterium of superconductivity is discussed.
Magnetic Freeze‐Out and Magnetic‐Field‐Induced Semiconductor–Semimetal Transition in Bi1−xSbx Alloys under High Hydrostatic Pressure
Authors: Kraak W. , Troppenz U. , Herrmann R. , Chudinov S. M. , Kulbachinskii V. A.
Published: July 2007

The galvanomagnetic properties of extremely pure single‐crystal Bi1−xSbx alloys (x ≈ 0.07 to 0.08) are investigated under hydrostatic pressure with static magnetic fields in the range 0 to 6 T. A striking anomalous behaviour of the longitudinal magnetoresistance (B ∥ C3) is observed in pure crystals (n < 1014 cm−3) which occurs as the magnetic field is increased above a certain critical value. At low magnetic fields and at high magnetic fields the electrical resistivity increases with increasing temperature in a metallic manner in contrast to the thermally activated behaviour observed at intermediate fields. A strong enhancement of the observed anomalies under hydrostatic pressure is found. An analysis of the results shows that the anomalous properties are associated with charge carrier freeze‐out effect in the intermediate field regime and a magnetic‐field‐induced semiconductor–semimetal transition in high magnetic fields. A simple schematic diagram of the band‐edge and impurity–level configuration of Bi1−xSbx alloys is proposed to describe the found experimental data.
Electronic Structure of the GeZnSe, GeGaAs, and GeAlAs(110) Interfaces and Superlattices
Authors: Kumar A. , Singh I.
Published: July 2007

The semi‐empirical tight binding method with sp3 s* basis is used for the electronic structure of GeZnSe, GeGaAs, and GeAlAs (110) superlattices. As the work of Vogl et al. shows, the inclusion of an excited s state s* in the basis set describes the lower part of the conduction band very well. Interface band structure, layer density of states, and charge transfer at the interfaces are given. Various interface states are differentiated between bound interface states and resonance states.
Nonequilibrium Thermalized Stage of Noble Metals
Authors: Heiner E.
Published: July 2007

Starting from first principles of quantum statistics a system of differential equations is derived by use of a time dependent projector technique. It describes the evolution of electron‐ and phonon temperatures in noble metal layers in the macroscopic thermalized (hydrodynamic) stage. Within numerical model calculations for gold results are obtained for the relaxation time which are in satisfying agreement with experimental measurements.
Magnetoresistance Behavior in Orthorhombic Crystals
Authors: Haritonidis J. H. , Kyriakos D. S.
Published: July 2007

The action of a magnetic field on any crystalline material is to induce an anisotropy in the electric resistivity even in the case of isotropic materials. In anisotropic crystals the natural anisotropy and the one imposed by the field act competitively. Thus the magnetoresistance behavior is peculiar because of the continuous change of the principal resistivity directions. A study of this behavior in orthorhombic crystals is made, based on the weak‐field phenomenological theory.
Orientational Vibrations of Two‐Dimensional Dipole Lattice on Support
Authors: Goichuk I. A. , Kukhtin V. V. , Petrov E. G.
Published: July 2007

The ground and metastable energy states are defined for a dipole system on a rectangular lattice. The latter appears when the ratio of lattice parameters becomes equal to 1.043. The spectrum of dipole vibrations is calculated with (and without) taking into account the mechanical coupling of dipoles with support for the 2D model of a lipid monolayer.
A Model for Lattice Dynamics of Lanthanides
Authors: Kushwaha S. S. , Dikshit M. P. , Srivastava S. K.
Published: July 2007

A simple model is proposed for studying the lattice dynamics of h.c.p. rare earth metals. The interaction between core‐core and (f, d)shells–(f, d)shells via conduction electrons is considered through a screened‐Coulomb potential. The direct Coulomb interaction between cores and (f, d)shell electrons is essentially short‐range and is, therefore, described through a non‐central type interaction extending upto the third neighbours.
Collective Excitations in Liquid Cesium Using a Theory of Phonons in Amorphous Solids
Authors: Rani M. , Pratap A. , Saxena N. S.
Published: July 2007

A theory of phonons in amorphous solids as developed by Takeno and Goda using a self‐consistent method, is applied for the numerical calculations of the collective excitations in the longitudinal and the transverse modes in liquid cesium at its melting temperature. The pair potential used for these calculations is the model potential obtained from Ashcroft's pseudopotential with Singwi's dielectric screening procedure for liquid cesium. An independent estimation of these collective excitations is done using the Hubbard and Beeby approach. Besides, an effort is also made to calculate the phonon lifetimes in the large wave vector transfer region where the collective excitations are observable. Results of the phonon dispersion obtained from these two methods are compared and good agreement is observed.
Anharmonic Properties of IV–VI Compound Semiconductors
Authors: Singh R. K. , Gupta D. C. , Sanyal S. P.
Published: July 2007

The anharmonic properties of IV–VI compound semiconductors are analysed by means of a theoretical model in which the charge transfer effects, arising from the deformation of electron shells leading to three‐body interactions, are included explicitly in the crystal potential energy. The agreement between the experimental and the theoretical results on anharmonic elastic properties is reasonably good in almost all the cases under consideration. The charge transfer effects show appreciable influence on the third‐order elastic constants and the pressure derivatives of the second‐order elastic constants of IV–VI semiconductors.
Dynamical Properties of the Molecular Crystals with Electrostatic Interaction Taken into Account. Low Pressure Ice Phases (Ih and Ic)
Authors: Belosludov V. R. , Lavrentiev M. Yu. , Syskin S. A.
Published: July 2007

Within the atom‐atom potential approximation including electrostatic interaction of charges localized on atoms, the dynamics of the molecular crystals is considered. Formulae determining some elements of the dynamical matrix are corrected and the dynamical properties of Ih and Ic ice phases are calculated. It is shown that taking into account the long‐range Coulomb interaction has an essential influence on vibrational frequencies and gives a possibility to describe the experimental data more precisely.
Monte‐Carlo Simulation of Exoelectron Energy Spectra
Authors: Lanteri H. , Rostaing P. , Bindi R.
Published: July 2007

A theoretical model is presented to calculate the energy distribution of exoelectrons. It is based on a Monte‐Carlo simulation method, under the assumption that electron motion is enhanced by the electric field created by surface charge. The computations are carried out in the case of MgO. The variation of the internal field with local modification of the surface charge, i.e. patch field effects, is considered. During the transport process, the electron–phonon interactions as well as the energetic and angular effects of the internal field are taken into account. The influence of the different parameters and particularly the temperature effects are shown.
The Identification of Urbach, Acceptor Impurity, and Phonon‐Assisted Components of the Optical Absorption Band Tail of n‐Type InSb
Authors: Allan G. R. , Mackenzie H. A. , Hunter J. J. , Wherrett B. S.
Published: July 2007

New measurements are presented of the interband absorption edge, in the range 0.01 to 100 cm−1, for uncompensated n‐type InSb obtained using a photo‐Hall technique. A spectral Urbach edge is observed in the range of sample temperature (20 to 77 K) and it is shown that the form of the experimental results derives from a broadening due to the interaction of acceptor impurity states. A phonon‐assisted component is also identified at sample temperatures above 40 K.
Modelling the Role of Electronically Excited States in Laser‐Assisted Phenomena
Authors: Wautelet M. , Gehain E. D. , Quenon P.
Published: July 2007

From available relations between thermodynamical and microscopic parameters, the role of electronically excited sites on bond breaking and atomic migration is studied. It is demonstrated that, in covalent materials, electronic excitation leads to a decrease of the activation energy for bond breaking and migration, and of the entropy for migration, and to an increase of the entropy for bond breaking. It is also predicted that, under some circumstances, laser excitation might give rise to a decrease of reaction rate above a critical temperature, independent on the photon flux. The shift of the equilibrium position between competing processes is discussed, in the presence of selective excitation. The previous arguments are compared with available experimental data. Hints for future experiments are given.
A Note on the Icosahedral Morphology of Ultrafine Metal Particles
Authors: Nara S.
Published: July 2007

A possible interpretation is proposed for the growth morphology of icosahedral ultra fine particles (UFP) of silver, the structure of which are identified as multi‐twin‐particles (MTP) consisting of twenty tetrahedrons having cubic structure accompanied by unavoidable strains or dislocations. It is shown that the stable structure of embryo has the icosahedral symmetry and the twenty triangular facets of icosahedron have the same intra‐planar symmetry with the (111) plane of the cubic close‐packed structure and they provide each a seed for the (111) epitaxial growth of the cubic crystal. It leads consequently to the occurence of the MTP‐icosahedron, near the grain boundaries of which, however, unavoidable lattice strain remains.
Calculation of Electron Velocity in Crystal ab Initio. Role of Relativistic Effects
Authors: Shilkova N. A. , Shirokovskii V. P.
Published: July 2007

The exact formula for the calculation of the electron velocity in the relativistic case is obtained by using the Hellman‐Feynman theorem and the perturbation theory for the matrices. The computation is performed along the symmetrical lines of 1/48th of the b.c.c. Brillouin zone for six energy bands of vanadium. A comparison with the appropriate nonrelativistic velocity values is made.
Self‐Consistent Calculations in the Theory of Mix‐Valence
Authors: Prabhu R. B. , Tangsali R. B.
Published: July 2007

Self‐consistent perturbation theory is employed for the calculation of physical quantities in mixed valence systems. A single impurity U → ∞ Anderson model is considered with and without crystalline field splitting. The main feature of this method is that excitonic and other correlations are included self‐consistently in the theory. In the case of crystalline or magnetic fields coupled non‐linear integral equations are obtained for conduction electron scattering amplitudes. These are solved iteratively by retaining the second order terms in the mixing term in the f‐electron Green function. Thus temperature dependent level shift and width for the f electron are obtained. Calculated are nf, the f level occupancy, the resistivity and thermopower both as functions of temperature, and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline E _{\rm f} $\end{document} the f level position relative to the Fermi level.
A Theory of Higher‐Order Correlations. II. Generalization to the Ising Model with Arbitrary Spin and to the Blume‐Capel Model
Authors: Šamaj L.
Published: July 2007

The method of Part I is extended to the Ising model with arbitrary spin S and to the Blume‐Capel model with uniaxial anisotropy Δ. The generalization from the case of spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document} is straightforward and the formalism does not require some extra complications. The values of the transition temperature for the spin 1 and spin ∞ Ising ferromagnets are to within ≈ 0.6% and ≈ 0.4% of series results, respectively. The results for the Blume‐Capel model are also in a remarkable agreement with high‐temperature series including the region, where MFA fails totally.