bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Estimation of Force Constant Change of Mössbauer 119Sn Impurity Nuclei in Palladium Host
Authors: Puri R. K. , Gupta L. R. 
Published: July 2007

AbstractPrecision measurements are made of the second order Doppler shift and absorption areas of the Mössbauer line of 119Sn, present as a dilute impurity in palladium lattice, over a range from liquid helium temperature to about 750 °K. The weighted mean temperatures have been determined from the moments ω(−2), ω(−l), ω(+l), and ω(+2) of the phonon frequency distribution in the palladium lattice as seen by the Mössbauer 119Sn impurity atoms. Assuming a Debye spectrum, ratios of the impurity‐host to host‐host spring force constants have been estimated from the characteristic temperatures on the basis of Mannheim's model of nearest neighbour central forces. The Sn‐Pd force constant has been found weaker than the equivalent Pd‐Pd force constant indicating the presence of resonance band modes without any evidence of localised impurity modes.
Multiple s‐Scattering in an Ideal Random Medium. II. Incoherent Transport and the Density of States
Authors: Lenk R. , Füger M. 
Published: July 2007

AbstractFor a disordered system of point‐like scatterers the density of states is calculated in two ways: firstly as usual with the Green's function method and then based on a general relation between the density of states and the normal “particle” density. This density is determined in two steps: firstly its coherent part as the absolutely squared coherent field and secondly its incoherent part as the solution of a classical transport problem. Velocity and mean free path of the incoherent radiation are identical with the corresponding quantities of the coherent field. This opens the way to get information on the transport behaviour of the disordered material if only the properties of the coherent field are known.
Born Model Calculations of the Properties of the Alkali Azides. II. Azide Librational Frequencies and Elastic Moduli
Authors: Welch D. O. , Danemar Å. , Royce B. S. H. 
Published: July 2007

AbstractSecond derivatives of the lattice potential energy, derived on the basis of a Born model of cohesion that has been modified to account for ionic asphericity, have been examined by calculating zero wavenumber azide librational mode frequencies and two elastic moduli for the tetragonal alkali azides. Comparison of the results with experimental data favors a dispherical representation of the closed‐shell repulsive character of azide ions over ellipsoidal representations.
Tensor Components of the Linear Magnetoconductivity of Warm Electrons in Many‐Valley Semiconductors
Authors: Asche M. , Sarbei O. G. 
Published: July 2007

AbstractThe tensor components for the linear magnetoconductivity and the square law deviations of the conductivity from Ohm's law are calculated assuming the existence of one relaxation time only. The results are discussed for the case of τ depending on energy only.
Interband Faraday Rotation and Ellipticity in Silicon Measured by Polarization Modulation
Authors: Metzdorf J. , Kessler F. R. 
Published: July 2007

AbstractInterband Faraday rotation has been measured in Si up to the first reversal in sign at 3.33 eV photon energy corresponding to the beginning of direct transitions at the zone centre. The direct gap is found to be (3.33 ± 0.02) eV at 300 K. The samples, very thin, self‐supporting films (d ≧ 0.1 μm), were obtained from epitaxial Si wafers. Faraday ellipticity as well as rotation has been measured to an accuracy of ≦ 10−5 using polarization modulation, which corresponds to a hundred percent magnetic field modulation. Faraday ellipticity, measured below 2.3 eV, is only associated with indirect transitions. But the Faraday rotation due to these indirect transitions calculated from ellipticity according to the Kramers‐Kronig relationship is at the maximum 2% of the total rotation. The influence of the direct and indirect transitions is discussed.
Processes Due to Optical Excitation of Impurities with One s‐EIectron (Ag0, Cu0, TP+, In2+, Ga2+) in KCI Crystals
Authors: Osminin V. , Zazubovich S. 
Published: July 2007

AbstractAt optical excitation of the electronic (A0) and hole (A2+) centres with 2S1/2 ground state (2S1/2 centres) in KCI crystals, polarized intra‐centreluminescence and destruction of the centres are observed due to the delocalization of electrons or holes. Localization of holes in the crystal, or interaction of electrons or holes with various crystal defects results in the formation of new centres (e.g. A0, Vk, Vk−T10 and Vk−T1+ pairs, H, A2+v−c). Luminescence is found to occur at the formation of new centres. Spectral, polarization, temperature, and concentration dependences are investigated for the phenomena observed.
On the Theory of Bloch Electrons in a Homogeneous Electric Field
Authors: Fiddicke J. , Enderlein R. 
Published: July 2007

AbstractA general expression for the solution of the time dependent Schrödinger equation of a Bloch electron in a homogeneous electric field is derived. For a special choice of the initial conditions Wannier's solution is obtained. An iterative solution procedure for the Wannier equation is given. A general formula of the density of states is discussed and applied tothe case of strong electric fields and weak periodic potentials.
Numerical Calculation of the Drift Diffusion Current for Elastically Interacting Point Defects
Authors: Pbofant M. , Wollenberger H. 
Published: July 2007

AbstractFor long range interactions the probability of defect encounter is determined by the drift diffusion current of one defect to the other. This current is calculated numerically for iso‐tropic point defects in an anisotropio elastic continuum. The diffusion current is found to be a fixed fraction of that caused by a spherical potential for which the current can bewritten by a simple analytical expression.
Optical Absorption of VI2
Authors: Van erk W. , Haas C. 
Published: July 2007

AbstractThe absorption spectra of single crystals of VI2 in the region6000 to 26000 cm−1 are reported. The spectra show a large number of narrow absorption lines which disappear above the magnetic orderingtemperature TN = 15 K. The absorption bands are assigned to electronic transitions of the d electrons of vanadium. From the spectra the ligand field splitting 10Dq = 7870 cm−1 and the Racah parameters B = 540 cm−1 and C = 2322 cm−1 are calculated. The results are compared with data for VC12 and VBr2.
Zubarev Green's Function of the s‐f Model for Magnetic Semiconductors and Its Relation to the CPA Solution
Authors: Rangette A. 
Published: July 2007

AbstractThe s‐f model for magnetic 'semiconductors is solved approximately with Zubarev's formalism without any decoupling. The solution is shown to correspond to the CPA solution for the self‐energy. Diagrams are introduced and a complete analysis of the problem is given. It is shown that the CPA solution is obtained by neglecting all diagrams which contain crossing interaction lines.
Atomic Configuration of 1/2 <111> {110} Edge Dislocations in Pure V, W, Mo, and Fe and in Fe Containing C Interstitials
Authors: De hosson J. Th. M. , Sleeswyk A. W. 
Published: July 2007

AbstractThe atomic configuration around a perfect edge dislocation with ‐1/2‐ <111> Burgers vector lying on a {110} slip plane is calculated using the Wilson and Johnson potentials for V, W, Mo, and Fe. The boundary conditions are given by anisotropic elasticity theory. A narrow dislocation without any stacking fault results but in all these metals somedisplacement occurs in the core parallel to the dislocation line. Johnson's iron‐carbon potential is used to calculate the positions with maximum energy gain for carbon atoms near these dislocations. The strongestbinding energy of the carbon atom of ‐0.70 eV is found for the di‐latational sink close to the dislocation line.
Perturbative Valence Charge Density of Trigonal Se and Te
Authors: Bertoni C. M. , Bisi O. , Calandra C. , Nizzoli F. 
Published: July 2007

AbstractThe electron valence charge density in Se and Te is calculated using perturbation theory to second order in an average form factor which accounts for the lion‐locality of the pseudo‐potential. The convergence of the perturbative expansion is tested and discussed, and a comparison is made with previous calculations derived from band structures. The importance of the second order term is related to the covalence of the chemical bond, lattice dynamics, and bonding charge models.
Magnetic Behaviour of the Dihydrate Formates M(HCOO)2 2 H20 of the Transition Metals M  Mn, Fe, Co, Ni
Authors: Burlet Paulette , Burlet P. , Rossat‐mraxod J. , De combarieu A. , Bedin E. 
Published: July 2007

AbstractMagnetic structures of the dihydrate formates of the transition metals (Mn, Fe, Co, Ni) are reported which are determined by means of neutron diffraction experiments. The magnetic moment directions are interpreted in terms of crystal field anisotropy. In order to determine the influence of anisotropy on the magnetic ordering some mixed compounds of manganese and iron formates are examined. For all these salts the metallic A ions (000, 01‐21‐2) linked together by formic groups show, below TN, a canted antiferromagnetic ordering. The metallic B ions (‐1‐2‐ 0, −1‐2− 0 ‐1‐2‐) not linked together show an ordered moment atlow temperature with respect to TN. In the manganeseand nickel formates the observed directions of the magnetic moments are notrelated to the axis of the oxygen octahedron and are due to a competition between the dipolar anisotropy and a weak single ion anisotropy. In the cobalt and iron counterparts the crystal field effects are strongly dominant and responsible for the observed moment arrangement. In iron formate the Fe2+ ions behave like a pure Ising model. The magnetic behaviour of the Mn formate is strongly affected by iron impurities. For iron concentrations higher than 0.1 the properties of the solid solutions are those of the pure iron salt since in the range of iron concentration 0 < x< 0.1 the solid solutions show a complex behaviour which can be interpreted by a variation of exchange and anisotropy energies.
Crystal Field Splitting in Octahedral and Tetrahedral Symmetry for Fe3+ Ions in Y3Fe5012
Authors: Vien Tran Khanh , Dormann J. L. , Le gall H. 
Published: July 2007

AbstractThe crystal field splitting of the energy levels of Fe3+ ions in octahedral and tetrahedral sites of Y3Fe5O12 have been computed between 10000 and 32000 cm−1. The calculation is performed using, first, the cubic field approximation, then the effect of a trigonal distortion, and finally the spin‐orbit interaction in the two magnetic sites. It is shown that the contributionof thetrigonal distortion to the absorption spectrum can be neglected. Thespin‐orbit coupling does not disturb the value of the calculated level energies but induces a coupling between some multiplets. With the use of the spin‐orbit coupling a very good fit between the computed and theexperimental spectra is obtained leading to an assignment of the observed absorption lines which is slightly different from that obtained without the spin‐orbit coupling effects.
Normal Inclusions in Type II Superconductors
Authors: Timms W. E. , Walmsley D. G. 
Published: July 2007

AbstractA modified local model of an isolated fluxline has been used to calculate the energy of a system of fluxlines and a magnetically reversible cylindrical normal inclusion. Strict attention to quantisation of fluxoid leads to forces which are comparable to those derived from simple considerations of condensation energy; they can extend to distances much greater than the coherence length. It is found that an analytical treatment of the same problem by Mkrtchyan and Shmidt, when generalised, can give the energy of the system to better than 10% in most circumstances.
Total Energy of Simple, Transition, and Rare Earth Metals and the Ionic Radii
Authors: Solt G. , Kollár J. 
Published: July 2007

AbstractA simple model is presented that gives an overall, semi‐quantitative description of the binding energy, equilibrium atomic radius, and bulkmodulus for simple, rare earth and IIIB‐VIB transition metals as well, by making use only of the valency (column number in the Periodic Table) and the value of the ionic (Pauling) radius. The two radius parameters of the modified empty‐core potential are linearly connected in the model, and both are correlated with the experimental ionic radius. The model, besides giving reasonable results for most of the simple metals, reproduces fairly well the cohesive parameters of the rare earth elements and the results are rather satisfactory also for transition metals up to the middle of each series.
The Theory of Sensitized Fluorescence in Solids
Authors: Golubov S. I. , Konobeev Yu. V. 
Published: July 2007

AbstractThe widely used Förster‐Galanin‐Dexter's (FGD) procedure of representation of the electronic excitation energy‐transfer rate between donor and acceptor impurity molecules, imbedded in small concentration in molecular crystals, is discussed by the overlap, integral of their light emission and absorption spectra. It is shown that this representation is only an approximative one, therefore a correction factor to the optical spectra overlap integral is given. This correction factor depends on the distance between donor and acceptor molecules and has a longer range in the case of the interaction of the donor and acceptor electronic excitations with acoustic phonons as compared to the interaction with optical phonons. The validity conditions of the representation mentioned above are discussed in detail.
Rate‐equation approach to stage II damage curves of metals in terms of the two‐interstitial model
Authors: Frank W. 
Published: July 2007

AbstractA theoretical expression describing the increase of the electrical resistivity of metals as a result of irradiations at temperatures in the recovery stage II is derived within the frame‐work of the two‐interstitial model of radiation damage. The derivation is based on the use of rate equations taking into account the following processes: simultaneous production of mobile crowdions or immobile dumbbell interstitials, and of an equal number of immobile vacancies; trapping or athermal conversion of both off‐line and on‐line crowdions at impurities, dumbbells, trapped crowdions or nearby vacancies; annihilation of crowdions at vacancies. It is shown that, as a matter of principle, the information which may be obtained from stage II damage curves cannot suffice to exclude the two‐interstitial model. On the other hand, under favourable circumstances stage II damage curves may enable us to demonstrate the validity of the two‐interstitial model unambiguously and thus to rule out the one‐interstitial model.
The path integral formalism as a new description for the diffraction of high‐energy electrons in crystals
Authors: van Dyck D. 
Published: July 2007

AbstractIt is shown that the Feynman path integral formalism provides an elegant way of describing the elastic scattering of electrons in crystals. Transformation of the formulae into momentum space permits the use of the Fourier transform of the periodic crystal potential so that the evaluation of the path integral results in a multiple sum. In the case of high‐energy electron diffraction, the introduction of the boundary conditions can be performed in a “forward scattering approximation”. It can be shown that the result obtained is equivalent with the solution of the system of Howie and Whelan, derived from the Schrödinger equation under a similar approximation. Applying a parabolic approximation to the multiple sum leads to the multi‐slice formulae of Cowley and Moodie. The kinematic and phase grating expressions can also be obtained using appropriate approximations.
Superconducting properties of lanthanum selenide
Authors: Sosnowski J. 
Published: July 2007

AbstractSuperconductivity phenomena in lanthanum selenide crystals with different electron concentration are observed. The parameters describing the superconducting state, in particular the critical temperature Tc and the lower critical field Hcl, are determined from measurements of the resistivity transition, the magnetic susceptibility and the Meissner effect on samples with various electron concentrations. From the experimental results the Ginzburg‐Landau parameter χ, the penetration depth λd, coherence length ξd, the Gorkov impurity parameter ϱ, etc. are deduced. The dependence of the critical temperature Tc on electron concentration is calculated on the basis of McMillan's theory and compared with experiment.
Use of representative points of the Brillouin zone for the self‐consistent calculations of solids in the large unit cell approach
Authors: Evarestov R. A. 
Published: July 2007

AbstractFor the self‐consistent (SC) calculation of solids an approach is suggested combining the “large unit cell” method with the theory of representative (special) pointsin the Brillouin zone. In the framework of the approach suggested the SC calculation of a solid can be realized by the self‐consistent methods developed for molecules. As an example cubic LiH, MgO, and KCl crystals are considered having face‐centered Bravais lattice. The SCCC (self‐consistent charge configuration) procedure used in molecular calculations is modified to be applicable for solids. Basing on the results obtained the character of the chemical bonding in the crystals considered is discussed.
Theory of free‐carrier absorption in n‐PbSe
Authors: Szymáski J. 
Published: July 2007

AbstractFree‐carrier absorption is calculated for n‐type PbSe using the model of a nonparabolic, nonspherical, and multivalley conduction band. New scattering mechanisms of the electron in PbSe‐like structure (two‐band deformation potential for optical phonons and twooptical‐phonon deformation potential) are considered in order to explain the recent experimental data on n‐PbSe.
Theory of interference between electronic and phonon Raman Scattering
Authors: Bechstedt F. , Peuker K. 
Published: July 2007

AbstractA theoretical treatment is given of continuous electronic and discrete one‐phonon Raman scattering for the case that the two scattering processes give rise to nearly the same Raman shifts. By using a Green's function formalism the final state interaction due to the interband electron–phonon coupling is described and it is found that the resulting line shape is similar to that of Fano's theory. A discussion is given of the frequency and the concentration dependence of the characteristic parameters.
Non‐Parabolic E(k) Relation of the Lowest Conduction Band in Bi2 Te3
Authors: Köhler H. 
Published: July 2007

AbstractElectronic maw parameters of the lowest conduction band in Bi2Te3 are determined from Shubnikov‐de Haas investigations in stationary magnetic fields up to B = 10.5 T induction. The electron concentrations ranged from about 2 × 1017 to 2 × 1019 cm−3. In contradiction to earlier reported results the cyclotron masses of the six‐valley ellipsoidal energy surfaces depend on the Fermi energy at various doping levels of the samples, though the ellipsoidal shape of the Fermi surfaces (with invariable ratio of the main axis) remains unchanged. The extrapolated band edge cyclotron mass for B parallel to the trigonal axis is 0.06m0 ± 5%, the density of states mass for one single valley at the conduction band edge amounts to 0.082m0 ± 10%, which corresponds to an integral density of states mass of 0.27m0 ± 10% at the band edge.
Electron and Phonon Spectra of Calcium
Authors: Taut M. , Eschrig H. 
Published: July 2007

AbstractA calculation of energy bands, electron density of states, and Fermi surface as well as phonon spectra, phonon density of states, Debye temperature, and elastic constants of calcium is presented and comparison is made with experiments. Shaw's model potential is used, however the parameter A1(ε′F) is fitted to an appropriate de Haas‐van Alphen‐frequency.
Optical Studies of Free and Bound Excitonic States in GaSb Evidence for Deep A+‐Complexes
Authors: Rühle W. , Jakowetz W. , Wölk C. , Linnebach R. , Pilkuhn M. 
Published: July 2007

AbstractThe energies of the free exciton and of four excitons bound to neutral acceptors (A°, X) are determined by either reflection, absorption, or emission with high purity p‐type GaSb. The data give evidence that bound excitons may be described alternatively as an electron bound by a donor‐like A+‐centre. For one particular deep A+‐centre, transitions from neutral donor states to that A+‐centre are observed besides the bound exciton decay. p‐GaSb is especially favourable for observing deep A+‐centres, because of the position of the Fermilevel. Conditions under which they may be observable for other III–V compounds are discussed.
The Effects of Surface Layers on Spin‐Wave Spectra in YIG Films
Authors: Ramer O. G. , Wilts C. H. 
Published: July 2007

AbstractExperimental spin‐wave spectra for thin magnetic (YIG) films have been matched by computations in which the surface boundary conditions were provided by thin surface layers with magnetic properties different from the bulk. In the case of annealed films, a diffusion layer between the film and its non‐magnetic substrate (GGG) is assumed to result from the thermal annealing. Thislayer is shown to produce a surface anisotropy field similar to the tensorial field postulated by Yu, Turk, and Wigen. This model accurately predicts the experimental spin‐wave spectra for all angular orientations of the applied field and qualitatively predicts the temperature dependence of the critical angle, the angle at which only the uniform mode is excited. Expressions for the resonance field and the critical angle are derived. The properties of the surface layers are discussed and the model is compared with experimental data from annealed and unannealed YIG films.
Multiphoton Absorption by Free Charge Carriers in Semiconductors
Authors: Pokatilov E. P. , Fomin V. M. 
Published: July 2007

AbstractThe absorption coefficient for intensive electromagnetic radiation is calculated for different scattering mechanisms in semiconductors: ionized impurities, polar and nonpolar optical interaction, deformation and piezoelectric interaction with acoustic phonons — at any temperature using the path‐integral method. The dependence on the intensity of partial multiphoton absorption coefficients as well as that of the total coefficient is investigated. In the cases of low and high temperatures the dependence of the absorption nonlinearity form on the scattering mechanism is studied. The possibility isrevealed to identify the dominant scattering mechanism on the base of experimental data on the nonlinearity of absorption.
Effective Electron‐Hole Interaction in Molecular Crystals (I)
Authors: Petelenz P. 
Published: July 2007

AbstractAn effective electron‐hole interaction is investigated which arises due to the one‐particle exciton dissociation matrix elements of the Hamiltonian. Fröhlich‐type unitary transformation is adopted and the transformed Hamiltonian is discussed. The exciton energy is renormalized. The sign and absolute value of the effective electron‐hole interaction is revealed to depend on the energy difference between the neutral exciton and charge transfer states. The influence of the vibronic coupling is also investigated.
Polytypism and Lattice Vibrations of PbI2
Authors: Grisel A. , Schmid Ph. 
Published: July 2007

AbstractRaman scattering and infrared reflectivity results are reported for the 2H and 4H polytypes of PbI2. The two polytypes can be clearly distinguished by their vibrational properties. The infrared reflectivity shows a broad reststrahlen band, pointing to the significantly ionic character of this compound.