bluuebunny/crossref_metadata_2025 huggingface dataset:
Acceptor States in Zero‐Gap Semiconductors in Magnetic Field. Theory for Short‐Range Defect potential
Authors: Gortel Z. W. , Szymański J. , Świerkowski L.
Published: July 2007

The high magnetic field behaviour of resonance acceptor states in zero‐gap semiconductors produced by short‐range defect potential is studied in the actual structure of an inverted Γ8‐band. Results of numerical calculations for different zero‐field acceptor level energies are presented and optical selection rules for transitions between acceptor states and Γ6 and Γ8 Landau levels are given.
Spectre de photoémission de l'alliage ternaire Ga1−xAlxSb
Authors: Ance C. , Amamou A.
Published: July 2007

Les mesures de photoémission UPS et XPS effectuées sur Ga1−xAlxSb montrent une modification des spectres de la bande de valence, en fonction de x, reliée directement aux structures de la bande de valence. L'évolution des énergies de liaison de Ga et Sb ne s'interprète pas directement par un transfert de charges, car la différence entre les énergies des niveaux internes de Ga et Sb reste inchangée quel que soit x. Ce résultat qui est en désaccord avec l'augmentation de l'ionicité, semble s'expliquer par une délocalisation de la charge transferrée vers l'anion.
Evaluation of the Fourth‐Order Elastic Constants of NaCl‐Structure Alkali Halide Crystals
Authors: Shanker J. , Singh J. P. , Gupta V. P.
Published: July 2007

All the fourth‐order elastic constants are calculated for 16 alkali halide crystals with NaCl structure using Lundqvist's three‐body potential energy expression. In addition to long‐range Coulomb interactions the short‐range overlap repulsive interactions are considered between first‐and second‐nearest neighbours as well as the van der Waals dipole–dipole and dipole–quadrupole interactions. Values of the fourth‐order elastic constants calculated in the present study are used to deduce the first pressure derivatives of the third‐order elastic constants and second pressure derivatives of the second‐order elastic constants for the crystals under investigation. The results are discussed and compared with available experimental data.
Thermoluminescence of Ag+‐Doped CsBr Crystals
Authors: Chowdari B. V. R. , Selvasekarapandian S.
Published: July 2007

Thermoluminescence and thermoluminescence emission of pure and Ag+ doped CsBr crystals are studied and the results are correlated with optical absorption studies. Two glow peaks at 356 and 393 K are observed in pure CsBr crystals. These two peaks are attributed to the first two stages of F centres. Four glow peaks at 348, 356, 366, and 393 K are observed in Ag+ doped CsBr crystals. While the glow peaks at 356 and 393K could be attributed to thermal decay of F centres as in pure CsBr, the 348 and 366 K peaks may be attributed to Ag° and Ag2+, respectively. Pure CsBr crystals give three thermoluminescence emission bands at 425, 450, and 475 nm. The origin of these three bands is discussed.
Energy Structure of the Alkaline‐Earth Fluorides
Authors: Starostin N. V. , Shepilov M. P. , Alekseev A. B.
Published: July 2007

The density of valence states for fluorite‐type crystals is calculated on the basis of tight‐binding (TB) and OPW methods. More precisely energy values of valence bands determined by the TB method at high‐symmetry points Γ, X, L are reported. A comparison is made with other theoretical estimates and experimental data.
Transition Temperature of Superconducting Alloys with Random Transfer Integrals
Authors: Kolley E. , Kolley W. , Beckmann A.
Published: July 2007

A formalism is developed to describe nonmagnetic weak‐coupling superconducting alloys in the presence of random transfer integrals of the additive type. The off‐diagonal disorder in the lattice space is treated within an extended version of the coherent potential approximation (ODCPA). Vertex corrections are performed by means of Ward‐type relations. The concentration dependence of the superconducting transition temperature Tc is determined. Numerical results are discussed in view of the sensitivity of Tc to different bandwidths of the components. A comparison with experimental Tc(x) data on TaxV1−x and TixV1−x is given.
Theory of the Free‐Carrier Absorption in Zincblende Narrow‐Gap Semiconductors
Authors: Sierańaski K. , Szatkowski J.
Published: July 2007

Free‐carrier absorption due to chemical disorder as well as to introduced intentionally periodic fluctuations of composition, is calculated in mixed semiconductors with the zincblende structure and dispersion relation that is typical for III–V and II–VI compounds. It is found that for low electron concentration, absorption coefficients due to chemical disorder and to ionized impurities are of the same order. Intentionally introduced periodic fluctuations of molar composition give an additional contribution to the absorption. This contribution for narrow period of the fluctuation (≈ 100 Å) has the form of a well defined peak.
Electron Structure and the Nature of Co3Ti Phase Formation
Authors: Tukhfatullin A. A. , Panin V. E. , Simakov V. I. , Demidenko V. S. , Kalyanov A. P.
Published: July 2007

A theoretical study of the electronic structure of the Co3Ti alloy is carried out in ordered and disordered states. The division of the ordered alloy energy spectrum into two band groups separated by an energy region of low state density is established. The genetic connection of the low and upper group of bands with atoms of different components and the character of wave functions in these bands are analyzed. On the basis of the calculation of the band energy the character of limited solubility of Ti in Co and the nature of the Co3Ti phase formation are analyzed for different alloy concentrations.
Padé Approximations for the Thermodynamic Functions of Weakly Interacting Coulombic Quantum Systems
Authors: Ebeling W. , Richert W. , Kraeft W. D. , Stolzmann W.
Published: July 2007

A weakly interacting system of electrons (e) and ions (i) is considered. Based on analytical formulae in the limiting regions of both weak and strong degeneration of the e4‐contribution and a few computer calculated points in the intermediate region n Λ3 ≈ 1 (n electron density, Λ thermal wavelength, Λ2 = 2πβh2/me, β = (kBT)−1, me electron mass) Padé‐approximations for the thermodynamic functions are constructed which are valid in the entire temperature–density plane. The temperature dependence of the exchange and correlation contribution to the chemical potential is taken into account here for the first time. In the framework of an unsymmetrical electron–hole model of germanium, a phase transition occurs with a critical point at Tc = 8 K and nc = 1.0 × 1017 cm−3.
Two‐Phonon Absorption Spectra in ϵ‐GaSe
Authors: Riede V. , Neumann H. , Lévy F. , Sobotta H.
Published: July 2007

Polarization‐dependent optical transmission spectra of ϵ‐GaSe are measured at room temperature in the wave number range from 180 to 600 cm−1. The absorption peaks observed can be interpreted in terms of two‐phonon combination modes including Γ, A, and M point phonons. The M point phonon frequencies derived from the two‐phonon absorption spectra are in good accordance with data previously published.
Volume Dependence of the Bulk Modulus in Alkali Metals
Authors: López J. M. , Alonso J. A.
Published: July 2007

The bulk modulus of alkali metals (calculated by the density functional method) is decomposed into a part due to the electronic gas, assumed homogeneous, and another part arising from the inhomogeneity of the electron density. The relative contributions of the two terms is studied as a function of volume and as a function of the ionic radius. The theoretical results for the bulk modulus and its variation with volume show very good agreement with the experiments.
Diagrammatic Perturbation Theory for a Spin–Phonon System
Authors: Barker G. C. , Tucker J. W.
Published: July 2007

In a diagrammatic expansion of the phonon Green function for a coupled spin–phonon system an essential quantity that enters the calculation is the polarisation matrix associated with the generalised spin susceptibility. Averages of time‐ordered products of spin operators that occur have been conveniently expressed in terms of semi‐invariants and are evaluated using a diagrammatic technique. Hitherto, only the zeroth‐ and second‐order contributions to the polarisation matrix are derived for a system of paramagnetic ions coupled to the phonons of the host lattice through an interaction that is linear in the strain. Near a spin resonance frequency, higherorder terms in the polarisation matrix become important. The complete expression for the fourthorder contribution to the polarisation matrix is reported. The result is valid for all temperatures and the concentration dependence of the paramagnetic ions is accounted for.
Internal Strains and Raman‐Active Optical Phonons
Authors: Anastassakis E. , Cardona M.
Published: July 2007

The connection between internal strains and Raman‐active optical phonons in crystals is discussed. In crystals with more than one atom per unit cell, there is usually a number of atomic position parameters which cannot be uniquely defined by crystal symmetry arguments. Within the present scheme, it is shown that those parameters correspond to the number of fully symmetric (Γ1, A1) optical phonons at q = 0. Besides lowering the symmetry of the crystal, an external stress can introduce new atomic position parameters (internal strains). The criteria are given for determining the type of internal strain which may be produced by an external stress. The internal strain is looked upon as a “frozen” Raman‐active phonon, both belonging to the same irreducible representation of the crystal point group. It is shown that the well‐known matrices of the Raman tensor can be used directly to determine the selection rules for the stress‐induced internal strains in all crystals, regardless of symmetry. Related unit cell crystal parameters can be determined with X‐ray diffraction techniques.
Energy of Magnetic Anisotropy and Reduction Symmetry of Crystals
Authors: Volkov V. M. , Kustov E. F. , Makietov T. K. , Steczko G.
Published: July 2007

Using the properties of reduction symmetry of the crsytals, the expressions for the energy of magnetic anisotropy (MA) for almost all symmetry groups are given. The newly introduced constants of the MA are calculated for some magnetic materials and the relationships between these constants and the constants generally used are given. The rules of behaviour of the new constants of MA in some crystals are analysed.
On the Kinetics of Phosphorescence and High‐Temperature Glow Peak in CaF2:Pr Single Crystals
Authors: Sinha R. K. , Mukherjee M. L.
Published: July 2007

Phosphorescence decay at room temperature (RT) and thermoluminescence (TL) are studied in CaF2:Pr single crystals following X‐irradiation at RT. With the increase of the doping concentration the TL increases initially, reaches a maximum, and then decreases slowly as the concentration is further increased. The order of kinetics is estimated for the phosphorescence at RT and the TL peak at 530 K. Corresponding values of trap depth (E) and frequency factor (S) are calculated by various methods. The trap depth for the phosphorescence decay and the TL glow peak is found to be 1.04 and 1.68 eV, respectively. The frequency factors estimated by several methods compare well and the average value of 1014 s−1 tallies with the result reported earlier.
Simple Non‐Local Calculation of Jellium Metal Surface Properties
Authors: Kiejna A.
Published: July 2007

The gradient expansion for the kinetic, exchange, and correlation energy contributions to the surface energy and work function of jellium metals is investigated. For the gradient correction of the exchange‐correlation the coefficient given by Geldart and Rasolt and the first gradient coefficient of Gupta and Singwi are used. The surface energy is determined from the variational principle for the energy, using parametrized trial functions for the electron density. The calculated surface energies are in agreement with some other nonlocal calculations. The work functions are calculated both, from the classical expression of Lang and Kohn and from less density‐profile‐sensitive expression. The calculated values of the work functions are in excellent agreement with the results of Lang and Kohn.
The Application of Kramers‐Kronig Relations to the Analysis of the Resonance Lines of Metallic Samples in ESR Spectroscopy
Authors: Jarosz J.
Published: July 2007

The application of Kramers‐Kronig (K‐K) relations is employed to the analysis of the shape of asymmetrical resonance lines observed for metallic samples, using ESR spectrometers. Intermetallic Gd1−xHoxAl2 compounds with x equal to 0, 0.01, 0.02, 0.03, and 0.04 are investigated, taking advantage of this method. For x equal to 0 and 0.02 samples are investigated, with particle sizes changing from 5 × 10−6 to 2.5 × 10−3 m. Agreement is found between the obtained results and those predicted by Dyson and Bloembergen. Using the pure absorption line separated from the observed resonance line, the g factor and the linewidth DH are calculated. Good agreement is achieved with the g and DH values calculated according to the method described by Peter et al.
Study of Anharmonic Properties of Alkaline Earth Oxides
Authors: Sanyal S. P. , Singh R. K.
Published: July 2007

The third order elastic constants, pressure derivatives of second order elastic constants, Anderson‐Grüneisen parameters, and second Grüneisen constants are calculated for alkaline earth oxides with the help of a new interionic potential. The potential consists of Hafemeister and Zarht (HZ) type short‐range overlap repulsion, effective up to second neighbours, van der Waals (vDW), and three‐body interaction (TBI) effects. The vDWI coefficients are calculated from the Slater‐Kirkwood variational method. The results obtained are in good agreement with experimental data.
Influence of the Interatomic Potential and the Elastic Scattering Cross‐Section Approximation on the Spatial Distribution of Implanted Ions
Authors: Burenkov A. F. , Komarov F. F. , Temkin M. M.
Published: July 2007

The elastic scattering cross‐sections are calculated both in the framework of Lindhard wide‐angle extrapolation method and on the basis of an exact solution of the classical equation of motion of a particle in a central‐force potential. Using a direct method for the numerical solution of integro‐differential equations governing the ion implantation spatial distribution parameters, the projected ranges, projected and lateral stragglings, and skewnesses are calculated in a wide interval of reduced energies. It is shown that for incident energies ε < 0.1 all these parameters are affected by the choice of both the interatomic potential and elastic scattering cross‐section approximation.
Thermoremanent Magnetization in Bi2O3 · Fe2O3 System
Authors: Banerjee B. , Sharma J. , Lahiry S.
Published: July 2007

All samples of Bi2O3 · Fe2O3 or BiFeO3, prepared by different methods, exhibit when recooled from 700 K in presence of a residual magnetic field (≈ 20 Oe) an unusual increase in susceptibility or magnetization near their Néel temperatures (≈ 540 to 600 K), and this behaviour is characterized as thermoremanent magnetization (TRM). Salient characteristics of TRM as documented by Néel are observed. Different possible mechanisms on the origin of TRM in these samples including the formation of fine lamellae of α‐Fe2O3 in Bi2O3 · Fe2O3 are discussed.
Lattice Dynamics of KCN and NaCN in the Anti‐Ferroelectric Phase
Authors: Anderson A. , Gash P. , Lüty F.
Published: July 2007

A simple force constant model is described which allows the zone‐center normal mode frequencies of potassium cyanide and sodium cyanide in their ordered anti‐ferroelectric phase to be calculated. The degree of translational—librational coupling is deduced from the eigenvectors, and relative Raman and infrared intensities are estimated. Results are compared with available experimental data, and good agreement is obtained for KCN. The simple model is, however, unable to fully explain the observed Raman intensity distribution in NaCN, and possible additional contributing mechanisms are briefly discussed.
Cooperative Jahn‐Teller Effect and Spin—Orbit Coupling In d‐Systems
Authors: Mironov V. S. , Ionova G. V. , Lubimov V. S. , Groznov I. N. , Ionov S. P.
Published: July 2007

The mutual influence of the Jahn‐Teller effect and spin—orbit coupling on the ground state of octahedral d‐complexes is studied. Jahn‐Teller ordering is found in island systems with KOsF6‐type structure.
Thermodynamic and Transport Properties of Crystals in Anharmonic Approximation
Authors: Malinowska‐Adamska C.
Published: July 2007

The thermodynamic and transport properties of the three‐dimensional body‐centred cubic lattice are investigated on the basis of the dynamical theory of anharmonic crystals. It is shown that the anharmonic effects of lattice vibrations are not negligible in calculations concerning the high‐temperature region. A comparison with experimental data is given for potassium theoretically described by various potential functions.
Van der Waals Theory of the Phase Transition in Quasi‐Two‐Dimensional Electron Gas in Magnetic Semiconductors
Authors: Baru V. G. , Grekov E. V.
Published: July 2007

A “liquid—gas” phase transition is investigated in a quasi‐two‐dimensional (quasi‐2D) electron gas in magnetic semiconductors. The quasi‐2D gas is produced by an external electric field in a metal—insulator—semiconductor system. The transition is due to s—f exchange interaction, which gives rise to a strong electron—electron attraction and, under certain conditions, makes the electron gas compression at the surface energetically favorable. The quantitative consideration is based on the analysis of the free energy functional obtained in the effective field approximation. Van der Waals isotherms and the phase diagram of the transition are plotted. The dimensions of electron liquid drops occuring for a given number of quasi‐2D electrons are estimated. Experiments for the detection of the phase transition are suggested.
Thermoluminescence of Heavy Metal Ion Doped Cesium Halides X‐Irradiated at Low Temperature
Authors: Chowdari B. V. R. , Selvasekarapandian S.
Published: July 2007

TL studies of CsBr, CsBr:Ag+, CsBr:Cu+, CsCl:Ag+, and CsCl:Cu+ crystals X‐irradiated at liquid nitrogen temperature are made. Both, undoped and impurity‐doped CsBr crystals exhibit two main glow peaks at 116 and 159 K. CsBr:Ag+ crystal exhibits three additional glow peaks (weak) at 133, 176, and 192 K. The main glow peaks in these crystals are attributed to the double migration of thermally activated Vk centers followed by a radiative recombination with trapped electrons. The formation and decay of these centers is supported by optical absorption studies. The formation of Ag0 and Cu0 and the enhancement of Vk centers is also discussed. Similar studies are made on CsCl:Ag+ and CsCl:Cu+ crystals. Two main glow peaks observed at 204 and 246 K in these crystals are attributed to Vk center as in the case of CsBr crystals. The glow peaks are analysed and the TL parameters are evaluated.
Range of Magnetic Interactions in Some Anhydrous Sulphates of the 3d Transition Metals
Authors: Wegener W. , Hautecler S. , Will G.
Published: July 2007

Several three‐parameter analyses are performed on β‐FeSO4, α‐FeSO4, α‐NiSO4, and α‐MnSOsb4 by selecting the exchange interactions among the set (J1, J2, J3, J4). These compounds disclose different spin configurations. As input data the experimental values for TN,χ(TN) are used and the second moments of the energy distributions of neutrons scattered by polycrystalline samples in their paramagnetic state. It is possible to determine the significant parameters. It is concluded that, in this series of compounds, the interactions extend up to the fourth neighbours, although the relative importance of the various parameters depends strongly on the ordering type.
EPR Study of a Triple Fine Structure in a 1d Alternating System: Cs2(TCNQ)3
Authors: Blanc J. P. , Dugay M. , Robert H. , Thibaud C.
Published: July 2007

The cesium salt of tetracyanoquinodimethan Cs2(TCNQ)3 exhibits a EPR spectrum showing a fine structure consisting of two doublets of equal magnitude. A theoretical interpretation is given using the alternating Heisenberg model characterized by two exchange integrals J and γJ with γJ ≦≦ hωe ≪ J. The distance d between the lines of the triplets and the linewidth ΔωI are theoretically determined for two behaviours of the four spin correlation function Ψ(t). Measurements of the angular dependence of d and the temperature and angular dependence of ΔωI, at 9600 and 35 000 MHz, imply that Ψ(t) = exp (—ωEt). Various theoretical parameters can also be calculated. Using the values obtained the theoretical and experimental angular dependence of the linewidth are compared at room temperature. The deviation from axial symmetry is also evaluated.
Site Effects on N and O Luminescence in Electron‐Irradiated Neon Films
Authors: Sayer R. J. , Prince R. H. , Duley W. W.
Published: July 2007

The visible luminescence spectrum of solid neon containing small amounts of N2 or O2 is investigated at 7.8 K using low‐energy electrons. Double‐doping experiments employing N2 and × (where × is either O2, CO or Ar) are also carried out. Particular attention is given to the interpretation of the α(N2D—4S) transition of matrix‐trapped N atoms, and to a lesser extent the β(O1S—1D) transition of matrix‐isolated O atoms. The spectral intensity distribution within these transitions is photoelectrically recorded and for the long lived α transition, afterglow spectra are also presented. The structure of the α transition is shown to depend upon both the ratio of the N2 and × concentrations as well as the total [N2 + X] concentration, for total guest concentrations in the range from 0.01% to 0.1%. The components which comprise this emission arise from N atoms trapped in two characteristic sites denoted “substitutional”‐ and “impurity”‐affected. This same interpretation also applies in large part to the β transition of trapped O atoms.
APW Research of Europium Monochalcogenides. I. Band Structures and Electron—Electron Interaction in Ferromagnetic Semiconductors
Authors: Farberovich O. V. , Vlasov S. V.
Published: July 2007

The augmented plane wave method (APW) is used for a theoretical study of the electron properties of europium monochalcogenides. Spin‐polarized energy band calculations of the ferromagnetic EuO, EuS, and EuSe explain qualitatively the exchange interactions therein. Based on the APW data in the frame of perturbation theory the Coulomb electron—electron interaction at the 4f shell of europium is taken into account for EuO and EuS. The band structures and the multiplet terms of the f6d and 3d94f8 excited states gives a new interpretation of a known experimental spectra for these compounds.
On the Electrical Conductivity and the Density of States for the Narrow‐Band Periodic Anderson Model in the Symmetric Case
Authors: Matlak M. , Zieliński J.
Published: July 2007

Starting from the exact atomic limit solution of the periodic Anderson model the electrical conductivity is calculated using the Kubo formula. Excluding very low temperatures the results remain in reasonable qualitative agreement with the behaviour observed experimentally for some intermediate valence compounds. The temperature dependent density of states function is also calculated and compared with the previous results.
Investigation of the Molecular Motions in Cd(NH3)6Cl2 by NMR Spectroscopy
Authors: Piśewski N. , Ferris L. T. H.
Published: July 2007

NMR results are reported for intramolecular motion in Cd(NH3)6Cl2. Below the 180 K phase transition, the motion of the NH3 groups is well described by the Hilt‐Hubbard theory with an activation energy of 9.63 kJ/mol. The inter‐proton distance in NH3 determined from relaxational measurements is 0.161 nm. Several K below and above the transition point, two phases with different spin‐lattice relaxation times coexist.
Theory of Optical Nonlinearities in InSb
Authors: Koch S. W. , Schmitt‐Rink S. , Haug H.
Published: July 2007

The gain and absorption of an electron‐hole plasma in pure InSb is calculated by including the effects due to the band‐gap renormalization and the band‐filling and by taking into account deviations from the parabolic band form. The intensity‐dependent changes of the index of refraction are obtained with the aid of the Kramers‐Kronig relation. The results explain the large optical nonlinearities which are observed recently in InSb by Miller, Smith et al.
A Calculation of Vacancy Formation Energies in Strontium Oxide
Authors: Richardson D. D.
Published: July 2007

A calculation of cation and anion vacancy formation energies in SrO is given after assessing three pair potentials, available in the literature, for their suitability. The calculation is done by a Born model including anharmonic potential effects and allows explicit relaxation of host ions about the defect. The vacancy formation energies are used to estimate a Schottky energy for SrO and this is compared with other available data on SrO and also several similarities of the present result with those of MgO found elsewhere are noted.
Influence of Crystal Field on the Magnetic Circular Birefringence
Authors: Malakhovskii A. V.
Published: July 2007

Magnetic circular birefringence (MCB) is decomposed into diamagnetic and paramagnetic terms for arbitrary values of the fields on the atom and the influence of crystal field on these terms in considered. It is shown that a crystal field is the necessary condition for an existence of the temperature‐independent term in the paramagnetic part of MCB and the properties of this term are considered taking into account the mixing of states inside and between atomic terms. MCB for the transition 3d1 → 4p1 in the cubic octahedral crystal field is found taking into consideration the mixing of states inside the atomic terms. Field and temperature dependences of paramagnetic MCB are calculated for this case.
Phonon Assisted Interband Optical Transitions in Semiconductors Sustaining a Coulomb Random Field
Authors: Iskra V. D.
Published: July 2007

The interband optical absorption coefficient is calculated by the semi‐classical method in the case of a Coulomb random field taking account of the many‐phonon effects. The Urbach rule is reobtained with a slope of the exponential edge which generally depends upon that heat generation parameter, the random field parameter, and the temperature. The temperature dependence of the reverse slope is close to the linear one if the temperature is not low. A satisfactory interpretation of the temperature dependence of the absorption edge in chalcogenide glasses As2Se3 and As2S3 is reached.
Growth of Semiconducting CdF2:Ho3+ Crystals and Study of Their Optical and Transport Properties
Authors: Pouradier J. F. , Grimouille G.
Published: July 2007

A method for growing CdF2:Ln3+ crystals (Ln lanthanide) is presented which results in semiconducting samples without any subsequent annealing. It is found that the main preparation parameters act on the optical and transport properties through a common parameter Eσ. The infra‐red absorption of the samples as well as their conductivity are then analysed in the frame of a model with impurity‐banding and hopping conductivity, resulting in informations on the impurity density of states.
On Quantum Theory of the Force Constant Matrix of Polyatomic Systems
Authors: Marushko I. A.
Published: July 2007

A method is developed within the limits of the Hartree‐Fock‐Roothaan approach for calculating the force constants of a polyatomic system. The problem of differentiating the matrix P̂ with respect to atom coordinates is solved (P̂ = ĈĈ*, where Ĉ is a column vector, the components of which are the coefficients of the electron wave function expansion over the basic set). The convergence of the iterative procedure in computing the derivative ∂P̂/∂R is shown to be determined by the same parameters as the convergence of this procedure in solving the Hartree‐Fock‐Roothaan equations. Explicit account of the translational symmetry of the crystal makes it possible to escape the differentiation of the matrix and to represent the force matrix of any order in the form of an explicit function of the derivatives of the matrix elements of the Hamiltonian, the unit operator, and the matrix P̂, determined in the course of the calculations of the electronic energy structure of the system. The method proposed is applicable to any kind of calculations of the energy structure which results in the solution of the secular equation.
Dielectric Properties of the Fast‐Ion Conductor Na3Sc2P3O12
Authors: Delbecq C. J. , Marshall S. A. , Susman S.
Published: July 2007

Dielectric properties of granular crystallites of the fast‐ion conductor Na3Sc2P3O12 are measured in the frequency range 0.05 to 26 MHz and the temperature range − 70 to + 125 °C. Plots of the loss tangent, at fixed frequency, vs. temperature show a very sharp change in tan δ accompanying a structural phase change at about 63 °C. These plots show two loss maxima in the low temperature phase which indicate the occurrence of two relaxation processes with activation energies of 0.49 and 0.77 eV. These relaxation processes are probably distinct from the process of fast‐ion conduction which occurs at temperatures above the phase change at 63 °C. The existence of the structural phase change is substantiated by heat capacity measurements.
Photogalvanic effect in piezoelectrics: Quantitative theory for interband transitions in gallium arsenide
Authors: Belinicher V. I. , Novikov V. N.
Published: July 2007

A quantitative theory of the photogalvanic effect for interband transitions in gallium arsenide is proposed. The photocurrent is expressed through the known crystal constants, and it possesses a characteristic oscillatory dependence on polarization and frequency of light.
A theoretical study of Raman scattering and infrared absorption spectra of Ga1−xInxP mixed crystals
Authors: Kleinert P. , Jahne E.
Published: July 2007

Using a Green's function technique a lattice dynamical study is carried out on the local density of states and the phonon‐optical properties for low concentrations of In atoms in Ga1−xInxP. The impurity‐induced Raman scattering and infrared absorption spectra are calculated for two cases: the nearest‐neighboui force constants A and B change equally or differently. One obtains reasonable correspondence of the calculated spectra to the recently observed features in the Raman spectra lying in the TA phonon region as well as to the already known structures in the Raman and infrared reflection spectra lying in the optical phonon region by assuming ΔA/A ≈︁ −0.6 and ΔB/B ≈︁ 0.
Shell models for B.C.C. transition metals
Authors: Khanna R. N. , Rathore R. P. S.
Published: July 2007

Four modified and simplified versions of the shell model due to Fielek are developed to describe the dispersion relations in tantalum and niobium. The models (model 1, 2, 3) thus developed adequately account for the cohesion, Cauchy's discrepancy, and anisotropy exhibited by the metals. It is found that the interactions coupling the nearby d‐shells are effectively angular for tantalum and central pairwise for niobium.
Stability of the peierls state due to impurities
Authors: Bulka B. R.
Published: July 2007

Stability conditions of the Peierls state in a one‐dimensional system with impurities is investigated. Calculations are performed in a single‐impurity approximation and two cases are considered: an impurity built in the chain and the system with solitons. In the first case the total energy of the system as a function of the atomic potential and the concentration of impurities is presented. In the case of solitons also the total energy is calculated and it is shown that for a few per cent con‐ centration of solitons the distorted phase is unstable. For polyacetylene the critical concentration of solitons is estimated to yc ≈︁ 5%.
Behavior of defects introduced by a nanosecond intense electron pulse at high temperatures in alkali halides
Authors: Toriumi K. , Itoh N.
Published: July 2007

Measurements have been made on decay curves of the F centers (vacancies) created with a nanosecond electron pulse in non‐treated and plastically deformed KBr or NaCl in a temperature range between 400 and 700 K. It is found that decay curves are decomposed into four decay stages: three bimolecular stages (referred to as stages I, II and III in order of increasing decay time) and a monomolecular stage (referred to as stage IV), which occurs at the last. The reaction rate constants for stages I and II are found to be not influenced by plastic deformation but those for the stages III and IV are strongly influenced. The pre‐exponential factors of the reaction rate constants for the stages I and II in KBr and for the stage I in NaCl are explained in terms of the recombination of the pairs of the isolated di‐H centers (di‐interstitials) and the F centers but those for the stage III in KBr and the stages II and III in NaCl are of the pairs of the trapped‐interstitials and the F centers. The stage IV is ascribed to the recombination of the F centers with the mobile interstitials released from the interstitial clusters, or the recombination of the mobile F centers with the interstitial clusters. The effect of the Na‐impurity on the decay curves for KBr is also studied.
Temperature dependence of the Righi‐Leduc coefficients for Na and K metals
Authors: Zhernov A. P.
Published: July 2007

For the first time the values of the Righi‐Leduc coefficient ARL for Na and K are determined within the framework of a microscopic pseudopotential model at low temperatures. It is shown, when neglecting the nonequilibrium state of the phonon subsystem that in order to find ARL for these alkali metals, it is sufficient to consider a set of one‐dimensional integral equations instead of the standard kinetic equation. An explanation is given of the experimentally revealed significant difference in the low‐temperature dependence of the Hall and Righi‐Leduc coefficients for Na and K.
Magnetic spin phenomena in the chlorophyll “a” photoconductivity
Authors: Frankevich E. L. , Tribel M. M. , Sokolik I. A. , Kolesnikova L. I. , Stolovitseii Yu. M.
Published: July 2007

Modulation of the chlorophyll “a” (Chl) photoconductivity by an external magnetic field due to variations of the rate of non‐equilibrium spin processes under the action of a magnetic field is observed. These processes are charge carrier generation and charge detrapping by Chl triplet. Application of a magnetic field causes two types of variations of the photoconductivity of Chl films in vacuum: (i) instantaneous (τ < 1 s ) increase of the photoconductivity and (ii) slow decrease with time constant τ = 10 to 100s. The influence of temperature and intensity of the exciting light on the magnetic field effects is investigated. A scheme of energy transformation processes in Chl involving electron‐excited and ionized states is presented. The presence of oxygen leads to an increase of the photoconductivity of Chl, as compared with the vacuum values, and to a change in the dependence of photoconductivity on magnetic field. These changes are shown to occur due to the appearance of new acceptor centres arising from unstable products of Chl photooxidation.
Direct absorption inside the electron‐hole liquid in Ge: Warping effects and final state interactions
Authors: Zimmermann R. , Rösler M. , Asnin V. M.
Published: July 2007

Earlier absorption experiments in highly excited Ge are successfully explained and quantitatively fitted by a theory including Moss‐Burstein shift in warped hole bands, self‐energy effects, and multiple electron‐hole scattering via screened Coulomb potential. The corresponding Bethe‐Salpeter equation is solved numerically in momentum space. At frequencies above Moss‐Burstein influence, calculated absorption spectra are close to the exciton continuum independent of excited carrier concentration in agreement with experiment, which disqualifies a one‐particle description of direct absorption in the electron‐hole liquid of Ge.
Absorption coefficients in the dynamical theory of electron diffraction for the non‐symmetrical Laue case
Authors: Sheinin S. S. , Kim H. S.
Published: July 2007

In previous investigations of diffraction contrast in the non‐symmetrical Laue case, the standard expressions for Bloch wave absorption coefficients, which are based on the assumption of symmetrical Laue diffraction conditions, are used. An expression for absorption coefficients which is specifically applicable to the non‐symmetrical Laue case is derived. For strong beam diffraction conditions it is shown that small errors result from the use of symmetrical Laue absorption coefficients in the non‐symmetrical Laue case. For weak beam diffraction conditions, on the other hand, considerable error can result. These errors increase with increasing crystal thickness and for increasing departure from symmetrical Laue diffraction conditions.
Calculations of Deformation‐Potential Constants in InSb
Authors: Gorczyca I.
Published: July 2007

The deformation‐potential constants for nonpolar optical‐phonon scattering and for acoustical‐phonon scattering in InSb are calculated. Wave functions obtained in the previous papers by orthogonalized plane wave (OPW) method and empirical pseudopotential method (EPM) are used to perform present calculations. The results are compared with those obtained from other theoretical methods and experimental data.
The Electronic Theory of the Alloy Systems Composed of Alkali Metal Elements. II. Phase Diagrams
Authors: Soma T. , Matsuo H. , Funaki M.
Published: July 2007

The phase diagrams of the Cs‐K, Cs‐Rb, Rb‐K, Cs‐Na, Rb‐Na, and K‐Na systems are investigated using the pseudo alloy atom model and the local Heine‐Abarenkov model potential. For the Cs‐K, Cs‐Rb and Rb‐K systems, the curves obtained near the melting point show reasonable agreement with experimental data, and the calculated results predict the presence of a mixture of two phases at low temperatures. Then, the Cs‐Na, Rb‐Na, and K‐Na systems show complete immiscibility.
Comparison of the s Band Structure of Face Centred Cubic and Hexagonal Close Packed Solids: II. Energy Correspondence
Authors: Betteridge G. P.
Published: July 2007

It is shown that an exact, one‐to‐one correspondence between the s band energies of the face centred cubic (3C) and hexagonal close packed (2H) structures exists throughout the common zone, when nearest neighbour interactions only are considered. The form of this correspondence throughout the zone, its physical basis, and the effects of more distant neighbour interactions, are discussed.
Non‐Local Calculations of the Dispersion of Electromagnetic Waves in Bismut: Dispersion Relation for the Voigt Configuration: q ∥ n ∥ C1, q ⟂ B
Authors: Saermark K. , Lebech J. , Braune W. , Kubicki N.
Published: July 2007

The dispersion and damping of Alfvén waves propagating through bismuth samples are calculated for the two Voigt configurations: B ∥ C2, q ∥ C1, E ∥ C3 and B ∥ C3, q ∥ C1, E ∥ C2 by means of a non‐local formalism developed earlier. A comparison with experimentally observed results is performed for a number of frequencies of the incoming microwaves.
Collective Motions in a Metal‐Doped Molten Salt
Authors: Kobayashi M. , Yokota J.
Published: July 2007

Gekoppelte Plasmon‐LO‐Phonon‐Moden und Polaritonen in einem metalldotierten geschmolzenen Salz werden als Kollektivbewegung mittels einer hydrodynamischen Beschreibung untersucht.
Lifetime of Photogenerated Carriers in TCNQ Single Crystals
Authors: Eley D. D. , Kinnear S. , Willis M. R.
Published: July 2007

Measurement of photocurrents using the variable frequency chopped light technique shows that the reported photocurrents are due to photogeneration of carriers rather than a bolometric effect. The carrier lifetime, which is 10 to 40 ms at room temperature is independent of wavelength, but dependent on temperature according to the equation τ = τo eE/kT with E = 0.255 eV.
The Coulomb Shift of the Charge Transfer Band in Donor‐ Acceptor Compounds
Authors: Mikhailov I. D. , Novikov S. V. , Vannieov A. V.
Published: July 2007

The mechanism of the shift of the charge transfer band ina three‐component donor‐acceptor system due to collective long‐range Coulomb interaction is considered. Correlations determining the critical value of the concentration of a third component, at which a dramatic leap of the charge transfer band to the long‐wave region occurs, are obtained.
Cluster Approximation and Perturbation Theory for Band Models with Coulomb Interaction
Authors: Lorenz B.
Published: July 2007

Band models with intrasite (Hubbard) and intersite Coulomb interactions are treated in a cluster approximation taking into account the interactions and the transfer within clusters of sites rigorously. Between different clusters the interaction is decoupled in a mean field approximation and the transfer term is treated as a perturbation. The ground‐state energy of the one‐dimensional Hubbard model is calculated up to fourth order in the perturbation and is compared with other approximations and the exact result. In the one‐dimensional spinless fermion model the perturbation is treated without further approximations by solving Dyson's equation for the one‐particle Green's function. The order‐disorder transition in this model is discussed.
Semiempirical Pseudopotential Calculations for the Electronic Structure of Zincblende Semiconductors
Authors: Singh I. , Srivastava G. P.
Published: July 2007

A semi‐empirical pseudopotential calculation is made for the electronic structure of zincblende semiconductors InP, GaAs, and CdTe. Using the local approximation, it is started with an ionic model potential, and screening it through the Heine‐Abarenkov dielectric function the pseudo‐potential is obtained. Various parameters in this pseudopotential are chosen so as to obtain good fit for important interband transition energies with experimental results. Band structures and electronic densities of states are presented and compared with earlier local ‐ and nonlocal‐pseudopotential calculations as well as with the available experimental results.
Thomas‐Fermi Approximation for the Valence Electron Densities in Cubic Semiconductors and Insulators
Authors: Baldereschi A. , Maschke K. , Milchev A. , Pickenhain R. , Unger K.
Published: July 2007

The validity of the Thomas‐Fermi approximation for the calculation of valence charge densities in cubic semiconductors and insulators is investigated. Starting from local soft‐core pseudopotentials the valence charge densities are calculated via full band structure calculations and by using the Thomas‐Fermi approach. The results obtained by the two different methods agree surprisingly well. It is found that the validity of the Thomas‐Fermi approximation decreases with increasing ionicity and covalency of the considered compounds.
Light Absorption in Semiconductors with Superlattice in Quantizing Magnetic Field
Authors: Chaikovskii I. A. , Shmelev G. M. , Enaki N. A.
Published: July 2007

The interand optical transition in semiconductors with superlattice (SL) in the presence of a quantized magnetic field are considered. Investigations are performed for two cases: H ∥ to the axis of SL, and H ⟂ to the axis of SL. In the first case the magnetic field affects the electron motion In the direction of the SL‐axis and the energy spectrum is determined in the effective‐mass approximation from the solution of Schrödinger equation which reduces to the Mathieu equation in the second case the energy spectrum is sufficiently anisotropic and has minibond character in the direction of the SL‐axis, but in the planes of layers an oscillatory structure. The selection rules for interband transitions are obtained for both cases. For H ∥ z the absorption coefficient has the form of a saw‐tooth curve; with increasing H the slope of the curve decreases, but the distance between peaks increases.
Theory of Multidomain States in the Ordered Phase of Crystals
Authors: Hudák O.
Published: July 2007

The existence of multidomain states in crystals within the Landau theory of continuous phase transitions is studied and is shown to be dependent on the number of independent directions of space modulation and on the presence of terms linear in derivatives of order parameters in thermodynamic potentials of crystals.
Refined Model of Exchange Inversion in Spontaneous Metamagnetism
Authors: Tuszyński J. A. , Cofta H.
Published: July 2007

The magnetic ions of an anharmonic crystal are assumed to interact through the Heisnberg exchange. In the temperature dependence of the exchange constants contributions from the lattice oscillations are included in addition to the usual exchange‐strictive term. The role of exchange‐striction in the metamagnetic transition is reexamined and a new eriterion for metamagnetism is formulated. An explanation for the lattice contraction of the Mn3GaC compound at the matamagnetic temperature is given and a paradox associated with previous theories is removed.
Localization of 3d‐Like Electrons in Cr‐Fe and V‐Fe Alloys
Authors: Szuszkiewicz M. , Rozenfeld B. , Chojcan J.
Published: July 2007

Localization of 3d‐like electrons at the atomic cores of the components of the b.c.c. alloys Cr1−xFex and V1−xFex is determined on the ground of positron annihilation and Mössbauer effect data and by taking into account certain assumptions concerning the interpretation of these results. For V1−xFex the electron transfer from Fe to V occurs in the whole concentration interval. In the case of Cr1−xFex the transfer from Fe to Cr takes place only for x < 0.65, whereas for x > 0.80 the opposite transfer (from Cr to Fe) occurs.
On the Polarization Dependence of Photoemission from Metals
Authors: Brodskii A. M. , Daikhin L. I. , Urbakh M. I.
Published: July 2007

The dependences of one‐and two‐photon photoemission currents from metal on angle of incidence and polarization of light are considered. They are found to be affected by the electric field intensity near the metal boundary. Unlike previous expressions for photocurrent, the formula derived includes an interference term between the amplitudes of probability of transition under the action of fields normal and parallel to the boundary. Experimental data on photoemission and electroreflectance of lead and indium are analyzed. Such a combined analysis may reveal certain essential electronic characteristics of the boundary, in particular, change in the phase of reflection of electrons on Fermi surface from the metal surface when its state changes. The effect of microroughness of the metal boundary on frequency and polarization dependences of photoemission is given special attention. The most significant effects arise in a frequency range where surface plasmons are created. The theory is consistent with experiments on photoemission from silver.
Soft X‐Ray Emission Spectra of Aluminium and Dysprosium from DyCo2–DyAl2 Intermetallic Compounds
Authors: Slebarski A. , Auleytner J.
Published: July 2007

It is shown that from the changes of the position and intensity of the L spectra of cobalt and aluminium and the NIV, V spectra of dysprosium in DyCo2‐DyAl2 alloys the following conclusions result: (1) cobalt is an acceptor of 3d electrons in the investigated compounds in agreement with the results of magnetic measurements, (2) the presence of the cobalt atoms does not change the character of the aluminium‐dysprosium bond, (3) on the high energy side of the Dy NIV, V spectrum the positive shift towards higher energy of the observed maxima which are connected with 4f → 4d transitions suggests a different band structure of DyAl2 in comparison to pure Dy.
Polarization‐ and Temperature‐Dependent Two‐Phonon Absorption Spectra in InSe
Authors: Riede V. , Neumann H. , Lévy F. , Sobotta H.
Published: July 2007

Polarization‐ and temperature‐dependent transmittance and reflectance spectra of InSe are measured in the wavenumber range from 200 to 500 cm−1. The absorption peaks observed are interpreted in terms of two‐phonon combination modes due to Γ point phonons considering the β‐, ϵ‐ and γ‐polytypes. It is concluded that the InSe crystals are of the γ‐polytype. Mode Grüneisen parameters are estimated for the intralayer modes.