bluuebunny/crossref_metadata_2025_split huggingface dataset:
Untersuchungen an abgeschrecktem und elektronenbestrahltem Wolfram
Authors: Kunz W. 
Published: July 2007

AbstractHochreines, zonengeschmolzencs Wolfram wurde in superfliissigem Helium abgeschreckt. Rei der Bestimmung der Leerstellen‐Bildungsenergie E aus Messungen des elektrischen Restwiderstands ist der Dickeneffekt berüeksichtigt. Isochronc und isotherme Anlß‐kurven ergeben komplexes Verhalten, was auf die Bildung von Leerstellenkomplexen hin‐deutet. Ergänzende isochrone Erholungskurven nach Elektronenbestrahlung bei 4,5 °K zeigen im wesentlichen drei Stufen. In Proben, die vor der Bestrahlung abgcschreckt wur‐den, verstärkt sich die Erholung im Tieftemperaturbereich. Dies stiitzt die Auffassung, daß beim Abschrecken tatsächlich Leerstellen und nicht Verunreinigungen eingefroren werden.
Relativistic generalization of the Saxon‐Hutner theorem
Authors: Subramanian R. , Bhagwat K. V. 
Published: July 2007

AbstractIt is shown how a delta potential can be replaced by appropriate boundary conditions for the wave function for the one‐dimensional Dirac equation. This technique is used to derive en explicit expression for the transfer matrix in the case of a linear chain of such potentials. Luttinger's proof of the Saxon‐Hutner theorem on band gaps is extended to the relativistic case by introducing necessary modifications.
On the temperature dependence of the DC conductivity in disordered materials
Authors: Croitoru N. , Popescu C. , Telnic M. , Vescan L. 
Published: July 2007

AbstractThe general expression of the conductivity σ(F) = f μ(E, T, F) f0,(E, T, F) g(E) dE is discussed, in which μ(E, T, F) is a generalized mobility which may depend on energy, field, and temperature. It is shown that constant activation energies result for sharply limited energy or mobility gaps and that a continuously temperature dependent activation energy may appear for a tailed‐type product μ(E) g(E). Expressions of the type σ ∼ exp (— B T−1/n) may be obtaincd even if the temperature dependence of the mobility is negligible.
The dependence of the energy gap on the composition in the mixed crystals CdνHg1νSe
Authors: Slodowy P. A. , Giriat W. 
Published: July 2007

AbstractThe dependence of the energy gap on the composition of CdνHg1‐νSe solid solutions has been determined from the measurements of the fundamental absorption edge. It has been found that, within the experimental error, E0 = E0(ν) exhibits a linear dependence. The coefficient of the temperature dependence on the energy gap with composition has been determined. dE0/dT1 has been found to be positive for ν < 0.4, and negative for x > 0.4.
Classical theory of nonlinear oscillators interacting with a medium
Authors: Dykman M. I. , Krivoglaz M. A. 
Published: July 2007

AbstractThe correlation function Qx(t) of the normal coordinates of singled out nonlinear vibrations interacting with the vibrations of the continuous spectrum of a medium (e.g. of local or quasi‐local vibrations in crystals) as well as its spectral representation Qx(ω) were investigated. The calculations have been carried out for the case of high temperatures when the classical approach is applicable. The use of asymptotic methods of nonlinear mechanics and some results of the theory of random processes allowed to consider the case of an arbitrary ratio between the constants characterizing the non‐linearity of singled out oscillators and their energy of interaction with the medium (but with the assumption that both these constants are small). In this general case asymptotic explicit expressions were derived for Qx(t) and Qx(ω). Using the Fokker‐Planck equation for this problem we have also derived the difference equations which determine Qx(ω).
Calculation of density of states for crystalline and amorphous III‐V semiconductors
Authors: Kramer B. , Maschke K. , Thomas P. 
Published: July 2007

AbstractThe densities of states of crystalline and amorphous Gap, GaAs, GaSb, InP, InAs, and InSb have been calculated using the pseudopotential method and the complex band structure (CBS‐)method. The short range order of the amorphous structures has been taken into account by an approximative correlation function.
Faraday rotation and the effective g‐values of excitons in cuprous halides
Authors: Suga S. , Koda T. , Mitani T. 
Published: July 2007

AbstractFaraday rotation spectra have been measured in the exciton absorption region on evaporated films of cuprous halides including CuCI, CuBr, CuI, and CuBr‐CuCl mixed crystals. From an analysis of the observed spectra, the exciton effective g‐ values are estimated and compared with a theory which takes account of the Zeeman, exchange, and spin‐orbit energies for the IS exciton states. Effects of the hybridization of the Cu 3d and halogen p orbitals in the valence bands in cuprous halides are quantitatively investigated.
Theory of singlet–triplet splitting of M‐ and Ft‐centres in ionic crystals
Authors: Berezin A. A. 
Published: July 2007

AbstractThe modified method of Gorkov‐Pitaevskii and Herring‐Flicker is used for the calculation of the value of singlet–triplet splitting in the system of two interacting F‐centres. The energy of singlet–triplet splitting (Δ) is expressed by a five‐dimensional integral in the configuration space of two optical electrons which for the case of 1s hydrogen‐like wave functions of F‐centres can be computed in explicit form. The numerical results are given for the M‐centre in alkali halides and the Ft‐centre (two electrons trapped by a linear trivacancy) in alkaline earth oxides (MgO and CaO). For these centres the calculated values of Δ are in good agreement with the experimental ones. It is shown that the theoretical values of Δ obey the Mollwo‐Ivery relation of the form Δ ∼ d−n (d lattice constant), where n ≈ 2.3 for the M‐centre and n ≈ 0.5 to 0.9 for the Ft‐centre.
Pressure and temperature dependence of the energy Gap in CdxHg1−xTe
Authors: Stankiewicz J. , Giriat W. 
Published: July 2007

AbstractThe investigation of the Hall coefficient in CdxHg1−xTe under hydrostatic pressure over the temperature range 77 to 300 K is reported. It is shown that within the experimental error, the energy gap is linear with x in the range 0 < x < 0.2. The pressure coefficient (dE0/dp)T and temperature coefficient (dE0/dT)p have been determined. The temperature coefficient of E0 has been found to be positive and to decrease with x. From the behaviour of RH = f(p) it has been established that the cross over Γ6, Γ8 is continuous.
On investigation of the structure of energy bands using quasielastic knock‐out of an electron by an electron (e, 2e)
Authors: Levin V. G. , Neudachin V. G. , Smirnov Yu. F. 
Published: July 2007

AbstractThe question of obtaining information on the band structure of solids using quasielastic knock‐out of an electron by an electron from a very thin crystalline film is discussed. It has been found that Van Hove singularities practically have no effect on the quasielastic knock‐out cross section. Form factors for the bands Γ1 Δ1 X1, Γ12 Δ1 X, Γ1 Δ1 L1, Γ λ1 L in a Cu single crystal have been calculated. The shape of the form factors is very sensitive to the type of electron binding in a crystal and to the hybridization of states in a single‐particle electron wave function. Form factors for a single crystal and a polycrystal of Al are also discussed.
ENDOR investigations on the superhyperfine interaction of Fe3+ in SnO2
Authors: Rhein W. , Rosinski Ch. 
Published: July 2007

AbstractENDOR measurements on Fe3+ at substitutional lattice sites of SnO2 show a well resolved superhyperfine interaction with the ten nearest Sn ligands and confirm a substitution of Sn4+ by Fe3+. The isotropic and anisotropic parts of the interaction are obtained. The spin Hamiltonian parameters of ESR are redetermined at 4.2 °K.
The temperature variation of magnetization of bulk amorphous Ni85P15: An amorphous ferrimagnet?
Authors: Simpson A. W. , Brambley D. R. 
Published: July 2007

AbstractThe variation of saturation magnetization with temperature of an Ni85P15 alloy has been measured with the sample firstly in the as‐deposited amorphous state and secondly in a crystalline metastable single phase condition. The Curie temperature of the amorphous sample was roughly three quarters that of the crystalline form, and the saturation magnetization at absolute zero of the amorphous sample roughly one third that of the ordered form. The corresponding states curve of the amorphous alloy was appreciably below that of its crystalline state which, in turn, was lower than that normally observed in ferromagnetic materials. The results are interpreted in terms of a large distribution in exchange interaction between neighbouring nickel atoms such that a significant proportion of the exchange coefficients are negative; an assumption supported by other radial distribution data. The moments of those atoms whose interactions are predominantly negative will tend to lie antiparallel to those of the bulk of the material thereby accounting for the low saturation moment at absolute zero of the amorphous sample. The name amorphous ferrimagnetism is suggested for such a phenomenon.
The precise evaluation of derivatives of the anisotropic elastic Green's functions
Authors: Barnett D. M. 
Published: July 2007

AbstractUsing Fourier transforms a simple scheme for numerically obtaining derivatives of the tensor Green's functions of elasticity with great precision is derived. The technique developed circumvents the need for solving an auxiliary eigenvalue problem and a related sextic algebraic equation common to previous treatments of this problem. Numerical results for the dilatation associated with a “dilatation center” in copper are given. The speed and accuracy of the present technique indicates that a previous suggestion by Lothe is indeed quite practical — namely, that internal stress problems (dislocations, point defects, inclusions, thermal stresses) in anisotropic media may be treated using tabulated data for the Green's functions and their derivatives.
Black–white contrast figures from small dislocation loops. I. Analytical first order perturbation solution
Authors: Wilkens M. , Rühle M. 
Published: July 2007

AbstractThe paper deals with a theoretical study of the black‐white contrast figures on electron micrographs produced by small dislocation loops under dynamical two‐beam conditions. The loops possess arbitrary orientations of their loop plane normals and Burgers vectors. The theory is based upon an analytical first order perturbation solution of the diffraction contrast differential equations of the Bloch wave type. An equation for the calculation of equal‐intensity contour diagrams is derived which can be applied easily without extended numerical computations.
On the theory of the infrared vibrational spectrum of a solid with structural disorder
Authors: Böttger H. 
Published: July 2007

AbstractA formalism is presented for the calculation of the infrared vibrational spectrum of a solid with structural disorder. A perturbation theory that takes an averaged field model as the unperturbed system is used to discuss one‐phonon selection rules. In zeroth order there is a q = 0 selection rule. In higher orders all vibrations are allowed to take part in the absorption.
Infrared reflectivity studies of p‐type Pb1 − xSnxTe
Authors: Korn D. M. , Braunstein R. 
Published: July 2007

AbstractNear normal incidence reflectivity spectra of p‐type Pb1 − xSnxTe have been obtained. The electric susceptibility effective mass m★, dielectric constant ε∞ and relaxation lifetime τ were determined by a computer least squares best fit of the data to a single band Drude free carrier model. A possible anomalous behavior of m★ has been observed.
Calcul de la conduetivité thermique du réseau par la formule de Kubo
Authors: Conan A. 
Published: July 2007

AbstractA l'aide de la formule de Kubo et dans le cadre de l'approximation de Hartree‐Fock, nous calculons, à partir d'un modièle hamiltonien simple, la conductivité thermique du réseau. Le temps de relaxation est calculé à l'aide de la méthode de la moyenne harmonique et conduit à une expression de la conductivité thermique à basse température en bon accord avec celle obtenue par la méthode variationnelle.
Zur Quantentheorie der Ionenkristalle. Eine Analyse der Lowdinschen Näherung
Authors: Bauer R. 
Published: July 2007

AbstractEs wird der Näherungscharakter der Löwdinschen Methode zur Losung der Hartree‐Fock‐Gleichungen für Ionenkristalle untersucht. Die Dichtematrix der Löwdinschen Nlherung (LN) geht über ein eingeschränktes Variationsverfahren aus dem Grundzustand der freien Ionen hervor. Der Einfluß des winkelabhängigen Anteils des kubischen Gitterpoten‐tials und der Austauschwechselwirkung der Nachbarn auf die Dichtematrix ist in der LN vernachlässigt. Die Auswirknngen der Löwdinschen Näherung auf die Beschreibung der Ionenbindung werden kurz diskutiert.
Photoconductivity associated with free excitons in GaAs
Authors: Richard C. , Dugue M. 
Published: July 2007

AbstractA peak of photoconductivity associated with free excitons has been observed in GaAs. This peak has been investigated as a function of the free electron density, the temperature, and the excitation intensity. A model which takes into account the dissociation of free excitons on ionized acceptors is presented to explain the presence of this peak.
Green's function theory of the polaron energy‐momentum relation
Authors: von Baltz R. 
Published: July 2007

AbstractThe energy E(p) of a polaron is studied as a function of temperature and momentum p with particular attention focused on the region where the excitation energy E(p) – E(0) closely approaches the energy of a longitudinal optical phonon. It is shown that in this region a quasi‐particle description is not adequate, e.g., the horizontal tangent in E(p) does not give rise to a singularity in the density of electronic states. The shape of the spectral weight function indicates that even for small coupling strength there is an internal excited state of the polaron.
The phase transition in solid orthohydrogen
Authors: Moraal H. 
Published: July 2007

AbstractA mean‐field theory for the phase transition in solid orthohydrogen is presented. For this particular form of the field it can be shown that the order‐disorder transition has to be accompanied by a change of crystal lattice. The transition temperatures found for o‐H2 and p‐D2 are 3.44 and 4.19 K, respectively, which values have to be compared with the experimental values of 2.91 and 3.99 K, respectively.
Density of states in the one‐dimensional Hubbard model
Authors: Elk K. 
Published: July 2007

AbstractFor the one‐dimensional Hubbard model with nearest‐neighbour interaction a functional equation is derived, which gives an exact solution for the density of states Dδ(ω). This functional equation is numerically solved for different values of the electron density nδ and the interaction strength U. From the resulting behaviour of the density of states, band splitting and an effective band narrowing is obtained. In the limit U → ∞ the band splits into several separate peaks.
Surface states in ionic crystals: Calculations for CsBr
Authors: Bertoni C. M. , Calandra C. 
Published: July 2007

AbstractThe Green's function approach has been applied to surface electron states together with a realistic model of bulk band structure of ionic crystals for the calculation of surface energy band structure of the (110) face of simple cubic CsBr. The results, which supply the first accurate test of the method, are in agreement both with the main trend of the experimental data for ionic crystals and with previous theoretical evaluations. Two main bands appear lying almost entirely inside the bulk band gap, the upper band has a metal‐like behaviour and the lower one is insulator‐like. This picture is confirmed also by the sketch of the electron density of states. It turns out from the calculation that the Green's function method is especially suitable for the description of electron states of not‐reconstructed surfaces.
Messungen der komplexen Dielektrizititszahl von Bariumtitanat‐Einkristallen bei Mikrowellenfrequenzen
Authors: Kaatze U. 
Published: July 2007

AbstractEs wird über Messungen der komplexen Dielektrizitätszahl von Bariumtitanat‐Einkristallen im Frequenzbereich zwischen 0,5 und 25 GHz berichtet. Sie wurden im para‐elektrischen Bereich nahe oberhalb der Curie‐Temperatur und im ferroelektrischen Bereich in der Umgebung der Kristallumwandlungstemperatur 5 °C durchgefiihrt. Aus dem Fre‐quenzgang der dielektrischen Verluste im paraelektrischen Bereich wird auf Polarisations‐fluktuationen und auf die Dämpfung der ferroelektrischen Gitterschwingung geschlossen. Im ferroelektrischen Bereich scheint ein Dispersionsverhalten mit Resonanzcharakter vor‐zuliegen in tfbereinstimmung mit Modellen von Kittel und Devonshire.
The effect on the spin resonance of conduction electroils in magnesium of a surface layer of oxide or nitride
Authors: Bowring C. S. , Cousins J. E. 
Published: July 2007

AbstractMeasurements are reported of the conduction electron spin resonance linewidths of magnesium, contaminated with surface layers of Mg3N2 and MgO, as a function of temperature and at a frequency of 9.27 GHz. The samples all had dimensions which were large in comparison with the skin depth and a temperature range of 200 to 600 °K was covered. The results are interpreted in terms of a temperature‐dependent intrinsic relaxation mechanism, a temperature‐dependent surface relaxation mechanism, and a temperature‐independent impurity relaxation mechanism.
The vibrational spectrum and dielectric behaviour of sodium chlorate
Authors: Dawson P. 
Published: July 2007

AbstractThe optical phonons of NaClO3 have been studied over a wide temperature range by Raman spectroscopy. It has been shown that the observed dielectric behaviour of this crystal may be accounted for solely in terms of the contributions from the polar phonons and that it is not necessary to postulate the existence of other dielectric mechanisms in the region between the microwave and far infra‐red regions. No evidence has emerged to support the suggestion that sodium chlorate is a fcrroelectric.
Stress study of the Jahn‐Teller effect in the 4T2, state of Cr3+ in α‐Al2O3
Authors: Duval E. , Louat R. , Lacroix R. 
Published: July 2007

AbstractThe vibronic wavefunctions of the 4T2, relaxed excited state of Cr3+ in α‐Al2O3 are determined when there are a Jahn‐Teller coupling with the Eg‐mode and a trigonal potential which cannot be treated as a perturbation with respect to the electron‐vibration interaction. The interaction Hamiltonian with a uniaxial stress, parallel or perpendicular to the C3,‐axis, is obtained. The experimental results are interpreted by the existence of a Jahn‐Teller effect with the Eg‐mode. Choosing 200 cm−1 for the vibrational quantum energy, the Jahn‐Teller energy is calculated from the experimental data.
Monte Carlo simulation on the behavior of energetic ions in polyatomic targets
Authors: Ishitani T. , Shimizu R. , Murata K. 
Published: July 2007

AbstractThe behavior of energetic ions in polyatomic targets is simulated by the Monte Carlo technique, which is based on a single scattering model taking account of nuclear and electronic stopping. The results follow the experiments fairly well as to range and energy distribution of transmitted ions through thin films. The present simulation is, in principle, applicable to any combination of ion beam and target.
Interprétation des structures magnétiques des composés TCo3 (T = Pr, Nd, Tb, Ho, Er)
Authors: Yakinthos J. , Rossat‐Mignod J. 
Published: July 2007

AbstractL'étude par diffraction neutronique des composés TCo3 montre que la direction des moments est fonction de l'ion terre‐rare considéré. Comme prevu par l'analyse des modes magnétiques on obtient des structures colinéaires, soit dans le plan de base (Nd, Tb, Ho), soit selon l'axe c (Pr, Er). La direction de ces moments est imposée par l'anisotropie du sous‐réseau TI, elle est par consequent une propriété intrinsèque de l'ion terre‐rare envisage et est déterminée seulement par le signe du coefficient a dans I'Hamiltonien de champ cristallin Hc = α V [3 Jz2 – (J + 1)].
Polarized luminescence of In++ and In++V centres in KCl:In crystals
Authors: Lukantsever N. , Osminin V. , Zazubovich S. 
Published: July 2007

AbstractPolarized luminescence is observed for In++ (hvmI = 2.12 eV) and In++v (hvmI = 1.75eV) centres in X‐irradiated KCl:In. Spectral and polarization characteristics of the luminescence are investigated. The symmetry of excited In++ centres is established to be tetragonal. The energy level diagram and the possible models of the In++ centres in the ground and excited electronic states are considered. It is assumed that In++ and In++v centres in the excited state may be represented as In+Cl and In+vCl quasimolecules, respectively.
Optical Anisotropy of Anthracene Single Crystals for Photon Energies from 4.5 to 11.5 eV
Authors: Koch E. E. , Otto A. 
Published: July 2007

AbstractReflection spectra between 4.5 and 11.5 eV were measured for near normal incidence (7.5°) with s‐polarized light from the (001) and (010) plane of anthracene single crystals at room temperature. The strong molecular 1B2u transition causes a strong anisotropic reflection band from the (010) face. By a Kramers‐Kronig analysis ε2 spectra have been obtained for the most important polarization directions. The Davydov splitting for the prominent excitation at approximately 4.5 eV, taken for polarization directions where no longitudinal contributions to the interaction lattice sums are present, is smaller than 0.05 eV. There is evidence, that a transition starting at 7.05 eV is polarized perpendicular to the molecular plane.
Infrared Active Two‐Phonon Processes in Some Alkali Iodides
Authors: Srivastavas S. P. , Bist H. D. 
Published: July 2007

AbstractThe infrared transmission spectra of NaI and KI have been recorded on a Beckman IR‐11 spectrophotometer using nujol mull technique at room temperature. Besides the fundamental absorption bands at the centre of the Brillouin zone, other lattice bands involving the interaction of infrared radiation with more than one phonon in the range 33 to 300 cm−1 have been observed. These multi‐phonon combinational bands (sum or difference) are explained in terms of the four characteristic phonons at or near the zone boundary and are consistent with the selection rules.
On the Theory of Optical Absorption Spectra of Disordered Semiconductors
Authors: Burtsev E. V. 
Published: July 2007

AbstractThe low frequency tails of the intrinsic and impurity optical absorption coefficients of nondegenerate semiconductors are calculated by the Green's functions method. The tails are due to the random force fields present in the samples. The fields are supposed to be generally anisotropic, Gaussian, and slowly varying in space. The intrinsic absorption tail has a Gaussian shape and a classical origin if the random fields acting upon electrons and holes are different. If the field is independent of the band index the absorption tail has a purely quantum origin; its shape depends somewhat upon the type of the field anisotropy and is close to exponential. As an example a special problem is considered in which the random field is provided by an intense acoustic noise flux propagating through the sample (both the deformation and the piezoelectrical interactions are considered). The results obtained are applied to interpret some experiments in which a modulation of an intrinsic absorption edge of piezocrystals by acoustoelectric domains was studied.