bluuebunny/crossref_metadata_2025_split huggingface dataset:
Band Structure Calculation of the Momentum Density in F.C.C. Manganese
Authors: Shrivastava S. B. , Ojha V. K. 
Published: July 2007

AbstractA band structure calculation of the photon‐pair momentum density distributions (TPMD) and electron momentum density for Compton scattering (EMD) in f.c.c. Mn is made employing Hubbard's approximate scheme. The results of the present calculations for TPMD and EMD in Mn along [100], [110], and [111] directions are analysed in terms of their respective band structures. A comparison of the TPMD results with the EMD shows that the high‐momentum component is much higher in the case of EMD. The results of ACPAR and CP are also presented.
Optical Properties of Amorphous GeS in the Spectral Region of 18 to 38 eV
Authors: Pajasová L. , Pajas P. , Makarov O. A. , Zakharov V. M. 
Published: July 2007

AbstractSynchrotron radiation is used in the measurements of the reflectance spectra of amorphous germanium monosulphide for several angles of incidence in the far ultraviolet region of 18 to 38 eV. The data are evaluated using a modification of the reflectance vs. angle of incidence method for extracting the information on n, the index of refraction, and k, the extinction coefficient. The values of the normal incidence reflectivity and the phase of reflection as obtained from n and k are matched to other experimental data of the spectral region from 0 to 18 eV. Finally, the optical properties of the material are evaluated in the whole spectral region from 0 to 38 eV. The resulting spectra of real and imaginary components of permittivity ϵ ‐ ϵ1 + iϵ2, as well as the derived quantities of −Im(1/ϵ), −Im(1/(ϵ + 1)), ϵ2ω2 and Neff, the effective number of electrons per atom engaged in optical transitions, are discussed and compared with available theoretical estimates.
Dielectric Function and Conductivity of p‐Type Semiconductors
Authors: Monecke J. 
Published: July 2007

AbstractThe frequency‐dependent dielectric function and the de conductivity of multiple‐band solids including interband transitions and finite life times are calculated in a relaxation‐time approximation for the example of p‐type semiconductors. It is shown that interband contributions to the dielectric function do not result in interband contributions to the dc conductivity.
Influence of Planar Defects and Disorder on the Energy Spectrum of Molecular Crystals
Authors: Primatarowa M. T. 
Published: July 2007

AbstractUsing the Green function approach the exciton spectrum of a molecular crystal containing planar defects is investigated. The system is presented in the nearest‐neighbour Heitler‐London approximation. The condition for the appearance of localized and quasilocalized states is obtained and the exciton energy is determined in a linear approximation in the defect concentration. Expressions are given for the density of states in some particular cases. Further, the energy spectrum of a disordered molecular crystal of a layer type is considered and the effect of the randomness of the interaction between the layers on the density of states is discussed.
Two‐Particle Solitary Waves
Authors: Mirjaniń D. Lj. , Marinkoviń M. M. , Kneževiń G. , Tošiń B. S. 
Published: July 2007

AbstractA method to analyse two‐particle solitary waves is proposed. The effects of exciton—exciton interaction are omitted. The probability amplitude as well as the energies of bisolitons are found. The probability amplitude represents a modulated plane wave whose spatial part is expressed over the centre‐of‐mass coordinate. It is shown that bisolitons are bound states of two excitations.
The Discrete Variational Xα‐Method Interpretation of the C KVV and Ti L2,3M2,3V Auger Spectra of TiC
Authors: Gutsev G. L. , Shulga Yu. M. , Borodko Yu. G. 
Published: July 2007

AbstractThe C KVV and Ti L2,3M2,3V Auger spectra are obtained for near stoichiometric TiC. Their interpretation is based on the results of the DVM‐Xα calculations of the Auger transition energies in a cluster approach and the evaluation of each transition intensity in the one‐centre approximation. The crystal structure is accounted for in the embedding cluster model. Theoretical values of the Auger energies and probabilities of transitions allow to describe qualitatively all the peculiarities of the TiC experimental spectra.
The Electron—Hole Plasma at Finite Temperatures. Calculation of Exchange‐Correlation Energies and Padeé Approximants
Authors: Rösler M. , Zimmermann R. , Richert W. 
Published: July 2007

AbstractThe thermodynamics of an electron—hole plasma is investigated with special emphasis on the temperature dependence of exchange (x) and correlation (c). The basic quantity of the RPA approach used, is the free energy as a function of density and temperature. In a wide density range a remarkable compensation is found of the temperature dependence between x and c which is exemplified for the chemical potential. Numerical results are presented with parameters modelling Ge and GaAs. For the phase diagram minor changes result compared with the usual approach taking xc at zero temperature. For practical purposes Padé approximants are constructed.
Crystal Electric Field Splitting in TbNi5 and ErNi5 Studied by Inelastic Neutron Scattering
Authors: Goremychkin E. A. , Mühle E. , Ivanitskii P. G. , Krotenko V. T. , Pasechnik M. V. , Slisenko V. V. , Vasilkevich A. A. , Lippold B. , Chistyakov O. D. , Savitskii E. M. 
Published: July 2007

AbstractCrystal field effects in polycrystalline samples of TbNi5 and ErNi5 are studied on the basis of inelastic neutron scattering experiments. Using the crystal field parameters derived from the neutron scattering the magnetic contribution of the specific heat capacity, the components of the static susceptibility, as well as the components of the magnetization are calculated, and compared with the corresponding experimental results for single crystals. The quadrupolar contribution of the crystal electric field B is related to the electric field gradients measured by TDPAC.
Calculation of Polarized K and L X‐Ray Emission Spectra and of Partial Densities of States of the H.C.P. Metals Be, Mg, and Zn
Authors: Rennert P. , Schelle H. , Gläser U.‐H. 
Published: July 2007

AbstractIntensities for polarized X‐ray emission spectra are given by the elements of the density matrix expanded with respect to lattice harmonics. These intensities and densities of states for special values of the angular momentum and special representations of the point group are presented for Be, Mg, and Zn starting from a pseudopotential calculation. The energy dependence and the anisotropy of the radial integration is investigated. It is shown that the anisotropic spectra can be described excellently by located densities of states. Non‐diagonal elements of the density matrix give the main contribution to the anisotropy of the LII, III‐spectrum of magnesium. The spectra are broadened and compared with experimental K‐spectra. A good agreement is achieved, some discrepancy remains concerning the size of the anisotropy.
A Study of Relativistic Interface States
Authors: Roy C. L. , Roy G. 
Published: July 2007

AbstractA relativistic study is made of the interface states in a solid which is reduced to a one‐dimensional system. The electronic states of such a model are governed by a two‐component Dirac equation. The interface connects two semi‐infinite solids represented by two semi‐infinite chains of δ‐function potential wells with a certain strength for either solid. In solving the Dirac equation for this model one is led to the energy—momentum relation of the system, that is to the band structure associated with non‐localised states and to isolated energy eigenvalues referring to interface states with certain complex momentum wave vectors. To eliminate isolated energy eigenvalues associated with states which increase exponentially towards the bulk on either side of the interface, existence conditions are derived which guarantee that only eigenvalues referring to interface states are selected. The influence of relativistic effects on the spectrum of interface states is demonstrated by choosing various sets of values for the parameters characterising the two solids. For the same purpose these interface state energies are recalculated for an approximately relativistic case using an approach by Steslicka and Davison, and for the strictly non‐relativistic case.
CoherentPotential Approximation for the Lattice Vibrations of Mixed III–V Crystals
Authors: Kleinert P. 
Published: July 2007

AbstractThe coherentpotential approximation (CPA) is applied to the lattice dynamics of some III–V mixed crystals. The calculations are based on an eleven‐parameter rigid‐ion model (RIM 11). Explicit results are reported for the one‐mode system In1−cGacP and the two mixed‐mode crystals In1−cGacSb and GaSb1−cGacAsc. Both, the reflectivity spectra and the composition dependence of vibrations at the Γ and X points are compared with existing experimental data. Force‐constant changes are considered by the virtual‐crystal approximation (VCA). The CPA theory is uniquely successful for III‐V mixed‐mode systems, which appear to switch from one‐mode to two‐mode behaviour.
Small Polaron Mobility in α‐LixO5
Authors: Sanchez C. , Henry M. , Morineau R. , Leroy M. C. 
Published: July 2007

AbstractESR and de conductivity measurements are performed on a α‐LixO5(x = 0.001) single crystal in the temperature range 4 to 293 K. They suggest that at low temperature, the unpaired electron remains localized in the field of lithium ion and is equally delocalized over four vanadium sites leading to the formation of a bound polaron characterized by a 29 hyperfine lines ESR spectrum. As the temperature is raised bound polarons are freed from the electrostatic field and the electrical properties of the sample above 250 K mainly arise from the hopping of free polarons between the vanadium sites. A comparison with previous measurements on non‐stoichiometric V2O5 shows that the activation energy corresponding to the hopping process of free polarons does not depend on the nature of the paramagnetic defect, but it appears that the energy needed to extract the bound polaron from the Coulomb field of the defect decreases when the overall radius of the defect increases.
Magnesium Colour Centres in NaF
Authors: Egranov A. V. , Nepomnyachikh A. I. 
Published: July 2007

AbstractThe absorption, emission, excitation spectra, and polarized luminescence of magnesium centres in sodium fluoride are studied. Three types of magnesium centres are observed. The first one, which is produced by X‐irradiation at 300 K and absorbs at 3.32 eV, is attributed to the Mgcentre. The two other centres have the electronic structure of the Mg0 atom perturbed by lattice defects. Optical excitation of the Mg0 type centres leads to two emission bands, which are attributed to the 3P1 → → 1S0 and 1P1 → 1S0 transitions. However, the structure of both of these centres are not still completly established.
Electrophysical Properties of Disordered Systems Based on Crystalline Germanium Compensated by Fast Neutron Irradiation
Authors: Konopleva B. F. , Evseev V. A. , Borisov B. A. , Nazarkin I. V. , Chekanov V. A. 
Published: July 2007

AbstractThe conduction of reactor fast neutron‐compensated n‐Ge (ND ≈ 1015 to 1019 cm−3) is studied. The formation of the disordered regions (DR's) is shown to generate an electrostatic potential which modulates the energy bands and affects strongly most of the electronic properties of a semiconductor. The DR‐compensated germanium is shown to possess most of the properties of the amorphous semiconductors. The Ohmic conductivity at low temperature (77 to 4.2 K) and the conductivity at moderate and strong electric fields at 77 K reveal a hopping nature.
Phonon Frequencies in GaAs
Authors: Patel C. , Parker T. J. , Jamshidi H. , Sherman W. F. 
Published: July 2007

AbstractThe eleven‐parameter rigid‐ion model is used to describe the lattice dynamics of GaAs. The model gives a satisfactory description of reported neutron scattering data throughout most of the Brillouin zone, and critical point phonon frequencies calculated with the model are shown to provide a satisfactory basis for the assignment of nearly all features in the reported two‐phonon infrared spectrum and second‐order Raman spectrum of GaAs.
The Coexistence of Unstable, Metastable, and Separated Frenkel Pair Defects in Solids. I. Basic Characteristics
Authors: Dzhumanov S. , Khabibullaev P. K. 
Published: July 2007

AbstractThe existence of unstable, metastable, and separated states of Frenkel pair defects as well as their coexistence in solids are theoretically studied. Existence region, lifetime, and equilibrium concentration of defects in these states are determined and a phase diagram of defect states for KBr is also drawn. The unstability (spontaneous annihilation) zone radius of charged and neutral pair defects are estimated. It is shown that this zone radius is very large for charged (particularly, for multiple charged) pair defects, while for neutral pairs it is about the interatomic distance. Unstable pair lifetime is estimated as ≈ 10−12 s, while metastable pair life strongly depends on crystal temperature and decreases rapidly with rising temperature. The results obtained are in good agreement with available experimental data.
Application of the Band Representations of Space Groups in the Theory of Electronic States of Crystalline Solids. II. Band Representations for Some Space Groups
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractThe simple band representations of the space groups O, T, and D are tabulated. The results of the band structure calculations for some crystals with the symmetry of these space groups are analysed from the point of view of the band representation theory. The possible applications of band representations in the electronic state theory of local defects in solids are discussed.
Electroreflectance and Thermoreflectance Spectra of SnSe Crystals
Authors: Valiukonis G. , Gashimzade F. M. , Guseinova D. A. , Krivaitė G. , Mamedov M. M. , Šileika A. 
Published: July 2007

AbstractThe electroreflectance and thermoreflectance spectra of SnSe crystals are investigated in polarized light with E ∥ a and E ∥ b. The direct energy gaps are 1.05 and 1.24 eV for light polarizations E ∥ b and E ∥ a, respectively. The polarization anisotropy of modulation spectra of SnSe is strong near the gap and becomes weak at higher energies. The structures of investigated spectra in the vicinity of the forbidden energy gap are interpreted by direct optical transitions on the high symmetry line Λ‐Γ‐V in the calculated energy band structure.
Optical Anisotropy of Transition Metal Dichalcogenides. A Photoelectrochemical Determination
Authors: Kautek W. , Decker F. , Gerischer H. 
Published: July 2007

AbstractPhotoelectrochemical quantum efficiency measurements with polarized light incident at either (1010) or (0001) faces of VIb‐VIa compound semiconductors can be a successful probing technique for the absorption anisotropy. A condition is that the diffusion length of minority carriers towards the crystal faces being in contact with electrolyte is smaller than the reciprocal absorption coefficient, and the real parts of the refractive indices are known. It is found that the observed absorptivity ratios x/az of MoS2, MoSe2, and WSe2 attain unity near the indirect absorption edge, but gradually become considerably greater than unity for wavelengths approaching the direct transition.
Semi‐Empirical Tight Binding Calculations for the Energy Bands of the Diamond and Zincblende Type Semiconductors
Authors: Sahu S. N. , Borenstein J. T. , Singh V. A. , Corbett J. W. 
Published: July 2007

AbstractA semi‐empirical molecular orbital theory is applied to study the band structures of the elemental (group IV) and III‐V compound semiconductors. The various parameterizational procedures of the elemental semiconductors are carefully studied and some of the results applied to the III‐V compounds to establish good sets of parameters for them. It is found that the orbital exponents are a set of very sensitive and important parameters in determining the correct shape of the bands in all the semiconductors.
Optical Properties of GeS
Authors: Lukeš F. , Schmidt E. , Humlíček J. , Dub P. 
Published: July 2007

AbstractReflectance and thermoreflectance are measured of single‐crystal GeS in the energy range of 1.2 to 5.2 eV in polarized light with orientations E ∥ a and E ∥ b. Kramers‐Kronig analysis is applied to all curves. Thus ε;1, ε2, Δε1, and Δε2 are obtained which are used together with the band structure of GeS calculated by Grandke and Ley and with the derived selection rules as a basis for the assignment of the characteristic energies to direct interband transitions at some symmetry points and along symmetry lines in the Brillouin zone. Some ellipsometric measurements are performed at 632.8 nm.
Calculation of the Resistivity of Liquid and Amorphous Au1−xSix Using Ziman Theory
Authors: Knuyt G. , Keupers A. 
Published: July 2007

AbstractThe Ziman theory is used in calculating the electrical resistivity σ and its temperature coefficient α for liquid and amorphous Au1−xSix. For the liquid the experimental σ(x) is rather well reproduced using Ashcroft pseudopotentials, while α(x) is better reproduced by the temperature variation of the mean structure factor than by the pure Ziman result. For amorphous Au1−xSix a model is proposed to calculate the various atomic structure factors from the experimental total X‐ray interference function. The resulting σ(x) and α(x) agree reasonably with experiment for x ≦ 0.3; in the other cases the Ziman theory fails, probably through the formation of localized states. It is concluded further that it can be a questionable assumption to take α equal to the variation of the structure factor at twice the Fermi wave number.
Thermoelectric Power in Inhomogeneous Metallic Polymers
Authors: Kuivalainen P. , Isotalo H. , Stubb H. 
Published: July 2007

AbstractThermoelectric power (TEP) in well conducting doped polymers is studied within a simple model in which the existence of metallic strands separated by thin potential barriers is assumed. It is shown that if the barriers dominate the dc electrical conductivity σdc(T) leading to a variable range hopping (VRH) conduction, they also give rise to a sub‐linear behaviour of TEP vs. temperature. The model predicts an enhanced TEP at high temperatures. It also indicates that due to the barriers the evaluation of Mott's parameters for VRH from the measured σdc(T) typically leads to incorrect values for, e.g., the density of states. The calculated TEP vs. temperature is compared with experimental data on heavily doped polyacetylene and polypyrrole.
Debye‐Waller Factor for Small Concentration of Mössbauer Impurities in Metallic Solids
Authors: Roy S. K. , Bhattacharya D. L. 
Published: July 2007

AbstractA simple theoretical analysis is presented of Mössbauer f‐values for 57Fe impurity in a general harmonic solid using double‐time Green function technique. An estimation of Mössbauer f‐values are made taking mass disordering and force constant changes into account and treating the mass and force constant changes within separable kernel approximations. The effective host‐impurity force constant ratios used in the present work span a range 0.40 < φ′φ < 1.30. Good agreement between the results obtained from the calculations and those reported earlier is found, indicating the validity of the approximations made during the evaluation of recoilless fractions. The temperature dependences of the mean‐square displacement are also obtained for three different cases.
Tracer Diffusion and Chemical Diffusion of Hydrogen in TaHx
Authors: Potzel U. , Völkl J. , Wipf H. , Magerl A. 
Published: July 2007

AbstractThe chemical diffusion coefficientDcand the tracer diffusion coefficientDtof H in α‐ and α≈‐phase TaHxare measured in complementary Gorsky‐effect (Dc) and neutron spectroscopic (Dt) experiments. WhereasDcandDtdiffer only slightly forx≈ 0.28,DcexceedsDtby a factor of ≈ 20 forx≈ 0.61. The difference betweenDcandDtis chiefly determined by the value of the thermodynamic factor which is additionally obtained in the Gorsky‐effect experiments. The large difference found for the higher concentration shows that neutron spectroscopic and NMR results forDtprovide only limited information on bulk hydriding kinetics in H storage compounds.
Photochemical Conversion of MA Centres and Identification of M Centres in CaF2:Na
Authors: Rauch R. 
Published: July 2007

AbstractThe photochemical destruction of MA centres in CaF2:Na leads at low temperature to the formation of a new centre with absorption bands at 325 and 445 nm and a fluorescence at 635 nm. The experimental results (dichroism after polarized bleaching, time and thermal behaviour) suggest the identification of the new centre as M centre. The great shift of the absorption bands relative to the MA or M+ centres is explained by the H model fitting method developed by Aegerter and Lüty.
Complete Analytical Solution for the Zero Bandwidth s—f Model
Authors: Nolting W. , Matlak M. 
Published: July 2007

AbstractThe s—f model, which describes an interacting system of localized magnetic moments and itinerant conduction electrons (magnetic 4f‐, 5f‐systems), is exactly solved in the zero bandwidth limit without further restrictions. The s—f exchange leads to a splitting of the S‐“band”; into four quasiparticle sub “bands”, the spectral weights of which are strongly temperature (T)‐ and carrier concentration (n)‐dependent. For special parameter constellations certain spectral weights disappear, so that corresponding excitations are forbidden. Besides the spectral weights some relevant correlation functions as the average spin‐dependent occupation number 〈nσ〉, the density correlation 〈nσn—σ〉 The “mixed” correlation Δ↑(↓) = 〈S(±)c〉 ± 〈S1n↑(↓)〉, and especially the spin‐polarization P = (〈n↑〉 – 〈n↓〉)/(〈n↑〉 + 〈n↓〉) can be formulated as very simple functions of T, n, and spin value S. It is found a qualitatively quite different behaviour of these functions for ferromagnetic s—f coupling (4f‐systems) and antiferromagnetic s—f coupling (5f‐systems).
Study at 0 K and Various Magnetic Fields of the Triangular Magnetic Configurations
Authors: Plumier R. 
Published: July 2007

AbstractAt 0 K in a magnetic field the behaviour is studied of a triangular configuration built of two species of magnetic ions of spin lengths S1, S2 acted on by unequal molecular fields. The magnetic interactions considered are the interaction J between first nearest neighbours (nn) as well as the interactions J1 and J2 between first nn of the same species. In such generalized Yafet‐Kittel configurations, three types of behaviours are observed, the most disclosing features being shown while taking S1, S2, J1, J2 as parameters and h, J as variables. A comparison is made between the stability of the triangular versus the biconical configurations. Whereas second order transition lines are observed in the (h, J) diagrams corresponding to the biconical configuration, first order transition lines as well as a triple point are expected in the case of triangular arrays.
Sequence of Ferrimagnetic Phases in Er2O2SO4
Authors: Kasten A. , Hoffmann J. 
Published: July 2007

AbstractBelow TN = 1.5 K Er2O2SO4 is an Ising antiferromagnet. In contrast to other RE2O2SO4 (RE = = Dy, Ho, Tb, Gd) the ordering is along the crystallographic c‐axis. In external magnetic fields applied along c the antiferromagnetic phase is left via intermediate ferrimagnetic structures with multiples of 1/8 of the saturation magnetisation and enters finally the paramagnetic saturated state. The main features of the experimental phase diagram are reproduced by mean field calculations.