bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Electronic Structure of Transition Metal Carbonitrides, Carboxides, and Oxinitrides. I. Theoretical Approach
Authors: Weinberger P. 
Published: July 2007

AbstractIn Part I of the paper the theoretical approach as used for a study of the electronic structure of TiCxN1−x, TiCxO1−x, and TiNxO1−x (Part II) and for the calculation of the “4f”‐binding energies in HfCxN1−x (Part III) is summarized. In particular Part I consists of a collection of formulas comprising the main aspects of the relativistic KKR‐coherent potential approximation (KKR‐CPA) especially with respect to its real space single site scattering (averaged t‐matrix, ATA) or multiplescattering (Cluster CPA) approximations as well as with respect to the angular momentum dependent local density of states and intensities for X‐ray emission.
Exciton Ground State in CdMnTe in a Magnetic Field
Authors: Cieplak M. Z. 
Published: July 2007

AbstractThe influence of the magnetic ions on the splitting of the ls exciton state in CdMnTe crystals in the presence of a magnetic field up to 4T is calculated using second order perturbation theory and including electron—hole exchange interaction. The results are compared with experimental data from the literature.
The Core Structure of an Edge Dislocation in NaCl
Authors: Puls M. P. , So C. B. 
Published: July 2007

AbstractA theoretical study is carried out to determine the core structure of (a/2) < 110 > {110} edge dislocations in NaCl and to investigate whether the dislocations dissociate. The calculations show that they do not. This result is opposite to the predictions of Fontaine and Haasen and the conclusions of Belzner and Granzer. The results are generated with the same point‐ion model (PIM) potential employed by Belzner and Granzer, plus a breathing shell model (BSM) potential due to Corish, Parker, and Jacobs. Core properties such as the stable symmetry type, the strain energy, and the Peierls stress are determined. Both potentials produce an approximately sinusoidally shaped Peierls barrier with a periodicity of one Burgers vector. The PIM and BSM potentials yield Peierls stresses of 80 and 17.3 MPa, respectively. Comparison of these results with low‐temperature flow stress data suggests that the BSM result is consistent with the experimental data whereas the PIM result is not.
Theoretical Investigation of the Current–Voltage Characteristics of Superconducting Niobium–Lead Tunnel Junctions
Authors: Seidel P. , Richter J. 
Published: July 2007

AbstractA proximity‐effect model for the niobium electrode is presented assuming on the barrier side the existence of a thin surface layer which differs from the other part of the niobium electrode. The resulting dependence of the quasiparticle current–voltage characteristic on temperature and electrode thickness shows good agreement with experimental results.
Analytical Description of the Resonance Dechanneling Effect in the Case of Axial‐To‐Planar Channeling Transition
Authors: Lenkeit K. , Wedell R. 
Published: July 2007

AbstractThe theory of resonance dechanneling under axial‐to‐planar transition conditions is further developed. For describing the structure of the atomic planes an analytical potential expression is used in the Thomas‐Fermi‐Molière approximation on the basis of Lindhards string of strings model. As a result of the investigation of the nonlinear equation of ion motion along the planar channel an expression is derived to calculate the tilt angle αmin required for planar channeling to be effective. This angle increases with increasing transversal coordinate in the planar channel. In this way the angular interval αmin < α < αmax is obtained which separates the axial channeling from the “pure” planar one. In a linear approximation of increasing transversal oscillation amplitude the initial amplitude is calculated, for particles which take part in the resonance of given order. The theoretical results are in sufficient agreement with numerical calculations and experimental values.
The Ground State of the Anderson Model. Variational Approach
Authors: Oleé A. M. , Chao K. A. 
Published: July 2007

AbstractThe ground state of the Anderson model is examined by means of the variational trial function which emphasizes interaction between the impurity electron and the electrons on the Fermi surface. Both, the number of electrons and the phase shift of the conduction electrons at the Fermi level are found to be continuous functions of the model parameters. The results reduce to the exact solutions at both the atomic and the strongly interacting system limits. They are compared with the Anderson solution in the Hartree‐Fock approximation, and the meaning of the local moment in both approaches is discussed. The local moment is shown to cause strong decrease of the impurity resistivity under increasing magnetic field at low temperature.
Renormalization Group and Critical Exponents for Classical Heisenberg Ferromagnet with Dipole–Dipole Interaction
Authors: Fakioǧlu S. 
Published: July 2007

AbstractThe renormalization group technique is applied to the three‐dimensional classical Heisenberg spin system with modified dipole–dipole interaction. For this system, the values and dependence of several critical exponents are investigated. These exponents are: α, the specific heat exponent; β and δ, the magnetization exponents; γ, the susceptibility exponent; η, the correlation function exponent; and v, the correlation length exponent. All the critical exponents except β depend upon the potential range σ. When the potential range σ = 3/2, the modified dipole–dipole results agree with mean‐field values of the critical exponents.
Mechanisms of Current Carrier Scattering in ZnxHg1–xSe
Authors: Gavaleshko N. P. , Gorley P. N. , Khomyak V. V. , Shenderovskii V. A. 
Published: July 2007

AbstractThe molar (vs. x), temperature and concentration dependences of mobility U = σR in ZnxHg1–xSe solid solutions with degenerate carrier concentrations are studied over wide ranges of temperature (77 to 300 K), concentration (1 × 1017 to 6 × 1018cm−3), and composition (0 ≦ x ≦ 0.15). The dominating scattering mechanisms and their peculiarities in the system of solid solutions studied, are established by comparison with U(n, x, T) dependence calculated by taking into account carrier scattering by acoustic and longitudinal optical phonons, impurity ions, and piezoelectric potential. A theoretical approximation is developed in the form of a formula describing the experimental results on band gap variation with molar composition and temperature.
Hyperfine Fields at Nonmagnetic Atoms on Various Sites in Ferromagnetic Heusler Alloys
Authors: Grover A. K. , Pillay R. G. , Nagarajan V. , Tandon P. N. 
Published: July 2007

AbstractThe hyperfine fields at Fe and Sn, as determined by Mössbauer effect and NMR, in a new Heusler alloy Ru2FeSn, are reported. By comparison with corresponding data in rhodium based Heusler alloys, it is inferred that a preferential R–Sn (R = Ru or Rh) disorder exists in these alloys. The hyperfine field data on Rh atoms occupying different sites in rhodium Heusler alloys helps to narrow the range of the parameter incorporated to account for the preasymptotic behaviour in the Blandin‐Campbell model of the conduction electron polarization. The calculations indicate for the elements of the s–p series occupying D site in traditional Heusler alloys that, if the change in sign of the hyperfine field occurs at the s2–p2 element (the hyperfine fields at s2–p1 and s2–p3 elements on D site being always observed to be negative and positive, respectively), then for s–p elements on (A, C) site, the change in sign will occur at the s2–p1 element and on B site, it will occur at the s2–p2 element but with the phase reversed i.e., the field at s2–p1 and s2–p3 is positive and negative, respectively. These predictions find strong support from recent experimental data in Heusler alloys.
Lattice Specific Heat of α‐Phase Alloys Based on Copper and Silver
Authors: Tiwari M. D. 
Published: July 2007

AbstractThe low temperature lattice specific heat is studied in detail in the α‐phase f.c.c. solid solutions of the following systems based on Cu or Ag: CuZn, CuGa, CuGe, CuNi, AgGa, AgGe, and AgIn. Except in cases of CuZn and AgIn where a reduction in lattice specific heat is obtained, other systems give an enhancement due to introduction of impurities. A defect model which includes the change in mass at the impurity site and the changes in the impurity–host crystal interactions around the impurity is considered. The effects of lattice expansion or contraction due to the substitution of impurities are also taken into account. For the systems having more than 5 at% of impurities the low‐concentration theory is modified. The calculated results compare well with the experimental data. It is observed in both systems (copper or silver based) that the changed lattice specific heat is quite sensitive to force constant changes. The contribution due to F1u‐symmetry modes dominates over all irreducible representations.
Exciton States in 1,2,4,5‐Tetrachlorobenzene Crystals and Dimers
Authors: Davidovich M. A. 
Published: July 2007

AbstractA calculation of the exciton interactions of the lowest triplet and singlet states in 1,2,4,5‐tetrachlorobenzene crystals and dimers is described. The results, including the effect of vibrations on the electronic interactions, are: (a) The splittings of the triplet and singlet dimer states for the equivalent dimer, located along the shortest crystal axis a, are, respectively, 4 and 16 cm−1; for the inequivalent dimer, located at the inequivalent sites in the unit cell, they are 0.01 and −0.4 cm−1, respectively. (b) The triplet band structure is essentially one‐dimensional. The triplet bandwidth and Davydov splitting are, respectively, 8 and −0.04 cm−1. (c) The crystal singlet Davydov splittings range from 2 cm−1, for k ‖ a−1, to 11 cm–1, for k ‖ c−1. The values obtained for the triplet interactions are one order of magnitude larger than the experimental ones. Possible reasons for this discrepancy are discussed. No experimental values on the singlet interactions are available for comparison.
On Magnon Damping in Antiferromagnets in Zero External Magnetic Fields
Authors: Breus S. A. , Sobolev V. L. 
Published: July 2007

AbstractIt is shown that the dipole–dipole part of the antiferromagnet Hamiltonian makes a small contribution both to the amplitudes of magnon–magnon interactions and to the coefficients of magnon damping. Possible relaxation mechanisms explaining the temperature‐independent part of damping, which is observed in the experiment, are proposed.
Temperature Dependence of the EPR Spectra of Cr3+ and Cr5+ Ions in CaV2O6 and BaV2O6 Crystals
Authors: Grunin V. S. , Patrina I. B. , Zonn Z. N. 
Published: July 2007

AbstractAn investigation is made of EPR spectra of CaV2O6 and BaV2O6 single crystals doped with chromium. It is found that the point symmetry of the paramagnetic Cr3+ and Cr5+ ions depends on temperature. It follows from the symmetry of the Cr5+ spectrum in BaV2O6 and its superhyperfine structure at T = 77 K that the Cr5+ ion is displaced to one of two neighbouring V atoms. The observed change of the impurity ion symmetry cannot be explained both by the off‐centre ion theory and the Jahn‐Teller effect.
Third‐Order Elastic Constants and the Pressure Derivatives of the Second‐Order Elastic Constants of Rare Gas Solids
Authors: Lehri S. , Verma M. P. 
Published: July 2007

AbstractExpressions für the third‐order elastic constants (TOEC) and the first‐order pressure derivatives of the second‐order elastic constants (SOEC) of rare gas solids are derived from a many‐body potential proposed in an earlier paper. The model parameters are evaluated from the three SOEC, the equilibrium condition, and (1) the experimental values of the pressure derivatives of the bulk modulus (dKT/dP) or (2) by approximating the three‐body potential to an exponential function. The values of the TOEC and the pressure derivatives of the SOEC evaluated by the two methods are tabulated.
On the Electronic g‐Faetor in n‐Type Silicon Inversion Layers
Authors: Englert Th. , von Klitzing K. , Nicholas R. J. , Landwehr G. , Dorda G. , Pepper M. 
Published: July 2007

AbstractThe tilted field method is used to measure the coincidence of spin‐split Landau levels of different Landau quantum numbers in (100) n‐type silicon inversion layers. At constant magnetic field perpendicular to the surface the peak values of Shubnikov‐de Haas oscillations are analyzed as a function of the tilt angle ϕ, where ϕ is the angle between the surface normal and the magnetic field. Pronounced maxima of s̀xx for Corbino devices and of s̀xx for Hall devices are found at the coincidence condition. The electronic g‐factor determined from the coincidence is substantially larger than the bulk value contrary to a recent publication, where experimental evidence for g = 2 was claimed. It is also shown that the Hall component does not falsify the results when the angular dependence of the resistivity maxima is investigated at constant total magnetic fields for a fixed Landau quantum number.
Huang Diffuse Scattering from Dislocation Loops
Authors: Larson B. C. , Schmatz W. 
Published: July 2007

AbstractNumerical diffuse scattering calculations are carried out for interstitial dislocation loops on {111} planes in aluminum using numerical displacement fields calculated for an elastically isotropic medium. Calculations are performed along selected directions near the (400), (200), (220), and (222) reciprocal lattice points. The results are found to be in qualitative agreement with the predictions of analytical diffuse scattering models; however, for quantitative results, detailed numerical calculations are found to be necessary.
Use of the Large Unit Cell Approach for Generating Special Points of the Brillouin Zone
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractA method for generating of special points in the Brillouin zone is suggested. This method is based on the “large unit cell” model and seems to be more general compared with those previously proposed. As an example, some sets of special points generated by this method for cubic crystals of class Oh with face‐centred and body‐centred Bravais lattices are given.
Relativistic Electron‐Phonon Interaction. Niobium and Tantalum
Authors: John W. , Nemoshkalenko V. V. , Antonov V. N. , Antonov Vl. N. 
Published: July 2007

AbstractThe theory of Gaspari and Gyorffy of the electron–phonon interaction is generalized to the relativistic case. Starting from the Dirac equation an expression for the Hopfield parameter η is derived in the rigid muffin‐tin approximation. As an example the Hopfield parameter is calculated for Nb and Ta by the relativistic APW method. The numerical results show that relativistic effects are important in Ta. However the direct influence of spin‐orbit interaction on the electron– phonon interaction is neglegible both, in Nb and Ta.
A Model Study of the Kohn Anomaly in the Optical Phonon Branch of a Binary Compound
Authors: Fong C. Y. , Weber W. 
Published: July 2007

AbstractLabbé's tight‐binding method is generalized and applied to a linear chain with two atoms per unit cell to study the Kohn anomaly in the optical phonon branch. The effects of various tight‐binding matrix elements on the anomaly are explored. The enhancement of anomaly can be effectively obtained by increasing the electron–phonon interactions.
Role of Three‐Body Interactions in Cohesive and Thermophysical Properties of Alkaline Earth Oxides
Authors: Singh R. K. , Sanyal S. P. 
Published: July 2007

AbstractThe cohesive and thermophysical properties of alkaline earth oxides are thoroughly investigated by extending Hafemeister and Flygare (HP) and Hafemeister and Zarht (HZ) potentials to include the three‐body interaction effects. The extended HZ potential thus obtained is found to yield a better description of the above properties than those revealed by the extended HF potential presented and many other potentials used by earlier workers.
Dynamic Spin Hamiltonian Formalism and Mössbauer Study of Spin—Lattice Relaxation of Paramagnetic Fe3+ (6S) Ions
Authors: Srivastava K. K. P. , Mishra S. N. 
Published: July 2007

AbstractIn a crystal field potential the 6S state of a paramagnetic 57Fe3+ (3d5, 6S) ion splits into three Kramers spin doublets Sz = ± 5/2, ± 3/2, and ± ½ and each doublet produces its own Mössbauer magnetic hyperfine spectrum at low temperatures as a result of the slow spin relaxation rate. These Mössbauer hyperfine spectra are used to study the temperature dependence of Fe3+ spin lattice relaxation rate falling in the region 106 to 109 s−1. The dynamic spin Hamiltonian formalism is utilised to explicitly calculate the spin—lattice relaxation rate of the three Kramers doublets for one‐phonon and two‐phonon processes in different temperature regions. It is further assumed that the various modes of acoustic phonon propagation are direction independent, the phonon spectrum is of Debye type, and the dynamic crystal field parameters are very similar to the static ones. It is found that for Fe3+ ions the one‐phonon relaxation process is most dominant and the theoretical results are in a very good agreement with the experimental observations. These calculations may be equally applicable to other S‐state paramagnetic ions.
Poisson Approximation to a Functional Approach for the Hubbard Model
Authors: Behn U. 
Published: July 2007

AbstractIn a previous paper the Green function for the Hubbard model is represented by a functional average of the Green function for an electron moving in a local time dependent potential Uvi(t) taking only the values 0 and U. Here this functional average is calculated with an ad hoc assumed Poisson distribution governing the jumps of Uvi(t). In a single‐site approximation the Poisson average can be calculated exactly and leads to a self‐consistent ‚dynamic’︁ scheme interpolating between band and atomic limit. For a half‐filled band in the paramagnetic case at zero temperature for strong Coulomb repulsion U ≈ 2 two subbands are obtained separated by a minimum of the density of states.
Raman Spectroscopic Investigation of Ferroelectric Phase Transitions in Rochelle Salt
Authors: Winterfeldt V. 
Published: July 2007

AbstractRaman scattering spectra of single crystals of Rochelle salt are recorded at 2 K and at several temperatures between 248 and 300 K in the spectral region from 0 to 4000 cm−1. The frequencies of some phonon modes soften or harden in the intermediate ferroelectric phase between the two Curie points which are known to exist in this material. In the paraelectric phases the frequencies remain constant. This behaviour can be explained by applying a simple nonlinear pseudospinphonon coupling theory originally developed for the TGS family and the incommensurate phase transition in thiourea. The anomalous specific heat due to temperature‐dependent optical phonon modes is also discussed.
Creation and Destruction of X Centres in Alkali Halides by X‐Radiation
Authors: Akilbekov A. , Nurakhmetov T. , Elango A. 
Published: July 2007

AbstractThe production (η ) and destruction efficiencies of X−3 centres in NaCl, KCl, KBr, and KI by X‐radiation versus the irradiation temperature (in the range of 80 to 320 K) are investigated by optical absorption and thermoluminescence methods. Both, the increase (80 to 150 K) and decrease (200 to 250 K) of η in KBr and KI at the adsorbed dose of 1019 to 1021 eV cm−3 are shown to be in correlation with the F‐centre creation efficiency (ηF). In chlorides ηF does not decrease with ηX−3 and these crystals are characterized by a high defect creation efficiency at approximately room temperatures. It is supposed that the creation of large halogen aggregates is much more efficient in chlorides than in bromides and iodides.
Four‐Photon Transitions in Semiconductors
Authors: Hassan A. R. , Raouf R. 
Published: July 2007

AbstractFour‐photon interband electronic transitions are theoretically investigated in semiconductors. Expressions for the absorption of four‐photons are calculated using fourth‐order perturbation theory for four different band models. The results show that the five‐band model gives the dominant contribution to the absorption coefficient. A numerical application for the case of ZnS is in agreement with available experimental results.
The Thermopower and the Thermomagnetic Power in Arsenic—Antimony Alloys at Low Temperature
Authors: Gitsu D. V. , Golban I. M. , Makeichik A. I. , Muntyanu F. M. , Onu M. I. 
Published: July 2007

AbstractThe thermopower and the thermomagnetic power at low temperatures (4.5 to 77 K) is investigated in AsxSb1‐x (x ⩽ 0.3) alloys. Peculiarities of the thermopower are observed, which are associated with the dragging of electrons by phonons. In magnetic fields B > 5 T the Shubnikovde Haas type quantum oscillation of the thermomagnetic power is displaid. It is established, that the AsxSb1‐x (x ⩽ 0.2) alloys are semimetals, and the overlapping of the energy extrema of L electrons and H holes increases, when arsenic is added to alloys.
Coherent Potential Approximation of the Relationship between Short‐Range Order and the Position of the Fermi Level on the State Density Curves
Authors: Batirev I. G. , Katsnelson A. A. , Kertész L. , Szász A. 
Published: July 2007

AbstractThe density of electron states of binary alloys of transitional elements with short‐range order is found using the coherent potential approximation. On the base of these calculated values the contribution of the band structure energy to the configurational part of the total energy is determined and the equilibrium value of the short‐range order parameter on the first coordination sphere is evaluated. The order parameters obtained for most the considered systems agree in sign with the experimental data.
EPR on Pb‐Doped ZnS Single Crystals
Authors: Dziesiaty J. , Backs D. 
Published: July 2007

AbstractEPR measurements are made on blue luminescent, Pb‐doped ZnS single crystals after excitation with light of 365 nm wavelength. The results are discussed in terms of a model similar to the ZnS A‐centre model assuming a ZnS vacancy associated with a neutral Pb2+ impurity on next cation site.
Electronic Structure of Fe3Si‐Type Alloys II. Correlation between Ordering Type, Band Structure, and Magnetic Moments
Authors: Blau W. , Himsel A. , Kleinstück K. 
Published: July 2007

AbstractOn the basis of the band structure described in Part I an interpolation scheme is discussed which allows to make a transformation of the band structures of the A2‐, B2‐, and DO3‐type lattices into another ones. For disordered alloys the CPA theory in split‐band approximation reveals a d‐band narrowing without changing the shape. For partially ordered alloys a combined model is proposed which gives a dependence of the magnetic moments on the proportion of pair probabilities in first and second neighbourhoods, in contradiction to former assumptions, which presume a dependence on the first sphere alone.
ENDOR Investigation of Atomic Hydrogen at Anion Sites in KCl
Authors: Heder G. , Niklas J. R. , Spaeth J. M. 
Published: July 2007

AbstractBy means of ESR and ENDOR the g‐values, the hyperfine (hf), and superhyperfine (shf) interactions of four shells of neighbours of atomic hydrogen and deuterium at anion sites in KCl are determined. The shf interactions are strongly temperature‐dependent and show large isotope effects. Both observations are due to vibrations of hydrogen. From the temperature dependence of the ENDOR data the frequency of the hydrogen vibrations could be determined.