bluuebunny/crossref_metadata_2025_split huggingface dataset:
F‐Centre Theory in Multivalley Cubic Crystals
Authors: Khazan L. S. , Pekar S. I. , Sheka V. I. 
Published: July 2007

AbstractThe interaction between an electron bound to a Coulomb potential and the LO lattice vibrations in a cubic multivalley ionic crystal is considered for not too weak coupling. The vibrational degrees of freedom in the partition function of the system are eliminated by Feynman's ordered‐operator technique. The complicated operator thus obtained depends only on the electron variables and is approximated by a suitable operator containing some available parameters. The latter provides to calculate the partition function of the F‐centre by means of a variational principle at arbitrary temperatures and thus to obtain the ground state energy of the F‐centre as a function of coupling parameters and of the anisotropy of electron band masses.
The Interaction of an Optical Polaron with Zero Vibrations of the Lattice in High Electric Fields
Authors: Shmelev G. M. , Sibirskii V. A. 
Published: July 2007

AbstractThe mobility of polarons interacting with zero acoustic vibrations of the lattice in high electric fields is evaluated. The polaron is described by the Feynmann‐Kadanoff model. The distribution function of such carriers is obtained as a solution of the Boltzmann equation, which is found to be never normalized. The effect of the escape of polarons in high electric fields leads, in principle, to the appearance of regions with negative differential conductivity in the voltage–current curve.
The Magnetic Properties and Indirect Exchange in Gd(Ni, Cu)2
Authors: Poldy C. A. , Kirchmayr H. R. 
Published: July 2007

AbstractThe magnetic properties of compounds in the Gd(Ni, Cu)2 pseudobinary system are described and the variation of the ordering temperatures with composition is accounted for in terms of the Rudermann‐Kittel‐Kasuya‐Yosida theory. In excellent agreement with experiment the model predicts a transition from the antiferromagnetic state of GdCu2 to the ferromagnetic one upon replacing 13% of Cu by Ni, where it is assumed that the 3d‐states of Ni are filled. Support for this assumption is obtained by considering the Curie temperature variation of the Ni‐rich end of this system in conjunction with the Gd(Co, Ni)2 system.
Energy Level Structure of Biexcitons and Related Optical Transitions
Authors: Bassani F. , Forney J. J. , Quattropani A. 
Published: July 2007

AbstractThe states of the biexciton molecule are related to the band structure of the crystal and effects due to spin–orbit interaction and to electron–hole exchange are taken into account. The cases of CuCl and CdS are explicitly studied and the possible bound states are given. Optical luminescence decay processes and two‐photon excitation processes are discussed and related selection rules are given. In the case of CdS all decay processes are shown to produce polarized photons. Experimental results are analyzed and are compared with theoretical calculations of the biexciton ground state energy.
Trigonal Warping of the Valence Band Fermi Surfaces of Tellurium
Authors: Köhler H. 
Published: July 2007

AbstractTrigonal warping of the valence band Fermi surfaces of tellurium, which was observed earlier by Shubnikov‐de Haas measurements for B ⊥ c (c trigonal axis), was investigated in detail from the oscillatory part of the magnetoresistance using arrangements for the magnetic induction B not normal to the trigonal axis of the crystals. Keeping the angle υ = ∡ (B, c) at 70° while rotating the samples around their c‐axis, a higher degree of reliability was achieved, where only fields up to 10 Tesla (100 kG) magnetic induction were necessary, and the observation of the effect was possible at hole concentrations of less than 1 × 1018 cm−3. Besides, a decision between the main influence of inversion or mirror symmetry of the trigonal warping on Shubnikov‐de Haas effect could be made for the first time. Numerical calculations were performed to fit the results using current ε(k) models of the valence band of tellurium.
Electric‐Field‐Induced Optical Activity and Circular Dichroism of Cr‐Doped KAl(SO4)2 · 12H2O
Authors: Weber H. J. , Haussühl S. 
Published: July 2007

AbstractThe effects of electrical fields on the optical activity and circular dichroism in chromium doped KAl(SO4)2 · 12 H2O crystals have been measured. Both effects are described by a third rank axial tensor, and therefore depend linearly on the electric field strength. The measured values agree with Vegard's rule. In the vicinity of the absorption band at 567 nm, both effects can be interpreted on the basis of a simple dispersion model.
Frequency‐Dependent Relaxation Time of Electrons in PbSe from Infrared Measurements
Authors: Mycielski A. , Aziza A. , Mycielski J. , Balkanski M. 
Published: July 2007

AbstractInfrared magneto‐reflectivity data for n‐PbSe are analysed and interpreted using a frequency‐dependent momentum relaxation time of free electrons. A peculiar variation of the relaxation time with frequency suggests a dissipation mechanism consisting in short‐wavelength plasmon generation.
Precipitates in Annealed and Quenched NaCl: Cd++ Crystals
Authors: Spengler W. , Kaiser R. 
Published: July 2007

AbstractRaman scattering, X‐ray, microprobe, and electron microscopy experiments show that precipitates of the crystallographic phase 6NaCl · CdCl2 are present in NaCl crystals doped with CdCl2 in the concentration range from 0.008 to 2.2 mol%. The size of the precipitates increases with increasing Cd concentration. If the NaCl: Cd crystals are quenched in a few seconds from 550 to 20 °C the main Raman peak is shifted to higher frequencies. This shift of the Raman peak is interpreted as being caused by the smaller size of the precipitates in quenched crystals.
Piezoemission Study of Free‐Exciton Exchange Interaction in CdS
Authors: Goede O. , Winter D. , Hasse E. 
Published: July 2007

AbstractThe free‐exciton exchange interaction in CdS is investigated by piezoemission measurements with static uniaxial stress σ ⊥ c and photon wave vector Kph ∥ c. The exchange‐induced splitting of the A(T5)‐exciton emission band and the stress dependence of the optical transition probabilities for the two components with polarizations E ⊥ σand E ∥ σ are measured at 77 and 27 K. The results are quantitatively discussed in the framework of the quasi‐cubic model for wurtzite‐type II–VI semiconductors and the exciton exchange parameter is determined in agreement with the zero‐field data of free exoitons in CdS. It is shown that the exchange parameter obtained by Langeretal. [l] from piezoreflection measurements is too large by about a factor of two because no corrections were made for the stress‐induced change of the transition probabilities increasing the experimentally observed splitting of the reflection minima.
Kinetics of Stress Relaxation in Normal and Superconducting States
Authors: Dotsenko V. I. , Landau A. I. , Pustovalov V. V. 
Published: July 2007

AbstractAn investigation is described of the kinetics of stress relaxation and postrelaxational effects in normal (N) and superconducting (S) states of polycrystalline 99.9995% pure lead at 4.2 °K. The work‐hardening coeificient θ(r) during stress relaxation has been found to be much larger than that θ(r) during dynamic deformation. It has also been revealed that θ(r)depends on the state of the sample (N or S state) where θ>θ.
The Pseudopotential Method and the Problem of Ordering in Alloys. II. Multi‐Ion Interaction
Authors: Krasko G. L. , Makhnovetskii A. B. 
Published: July 2007

AbstractThe problem of multi‐ion interaction in ordered alloys is considered. Khachaturyan's theory of ordering is modified to take into account this interaction. A pseudopotential approach is developed and a procedure suggested to calculate the “main” terms of third and fourth order perturbation theory including the effects of the Fermi‐surface distortion. Expressions are found for the thermodynamic characteristics of alloys in terms of pseudo‐potentials of ion‐components.
Observation of Magnetostriction in Cu Ferrite Single Crystals
Authors: Arai K. I. , Tsuya N. 
Published: July 2007

AbstractThe magnetostriction constants λ100 and λ111 of Cu ferrite single crystals quenched from 820, 900, and 950 °C were measured by a capacitance method in a temperature range from liquid N2 to room temperatures. For the crystal quenched from 900 °C, the magnetostriction constants λ100 and λ111 at room temperature are −87.3 × 10−6 and 9.8 × 10−6, respectively. The absolute value of the constant λ100 has a maximum (about 200 × 106) near 155 K, and the maximum value decreases with the increase of the quenching temperature, while the value of the constant λ111 decreases monotonically with the increase of the temperature.
Optical Phonons in ZnGeP2 and CdGeP2
Authors: Bettini M. , Miller A. 
Published: July 2007

AbstractThe phonon spectra of ZnGeP2 and CdGeP2, determined by Raman scattering on single crystals at room and liquid nitrogen temperature, are presented. The close coincidence of the zone center phonon energies of ZnGeP2 with the corresponding τ, X, and W modes of its isoelectronic analogue, GaP, bears out the expected similarity of lattice vibrations in ternary chalcopyrite compounds and binary zincblende materials. Differences between ZnGeP, and CdGeP2 can be attributed to mass and force constant differences when Zn is substituted by the heavier Cd atom.
The Dynamics of Molecular Crystals under Pressure
Authors: Pawley G. S. , Mika K. 
Published: July 2007

AbstractA general procedure for the calculation of the lattice modes in molecular crystals under pressure is given. Only a few modifications are necessary to the general lattice dynamical computer program. Calculations have been performed and the results are presented for naphthalene, anthracene, and orthorhombic sulphur. Although the basic program uses a sum over atom‐atom interactions to derive intermolecular interactions, this is not a necessary assumption in the procedure for the application of pressure. For naphthalene and anthracene the calculated increase in phonon frequency per kilobar of pressure is roughly 0.045 and 0.12 THz for modes with frequency 2 and 6 THz, respectively. Not all modes behave in this manner, and so the calculated pressure variation could prove very useful in mode assignment. The effect of uniaxial pressure on orthorhombic sulphur was also investigated, showing a markedly different frequency variation for some modes but not for others. Thus uniaxial pressure, if experimentally possible, could prove further the success of mode assignment. At 23 kbar uniaxial pressure the orthorhombic structure of sulphur became unstable, resulting in a monoclinic form in the space group C2/c. It is of interest that the simple model for intermolecular interaction can predict a soft mode phase transition, though whether this occurs in practice remains to be seen.
Impurity Effect on the Metal–Semiconductor Transition of NiS
Authors: Ohtani T. , Kosuge K. , Kachi S. 
Published: July 2007

AbstractImpurity effects on the metal‐semiconductor transition of hexagonal N P have been investigated by magnetic susceptibility, electrical resistivity, and thermoelectric power measurements. The transition temperature Tt is raised by addition of Ti, V, and Fe, and lowered by the addition of Co and Cu. Cr ions do not seem to be dissolved in NiS lattice. The sample containing 2.0% Cr shows, however, a negative Seebeck coefficients below Tt, which implies electron conduction, in contrast with pure NiS. Conduction electrons in this phase seem to be produced from sulfur vacancies. The transition mechanism is explained by the electronic phase diagram based on the Mott‐Hubbard model.
The fluorescence properties of crystalline anthracenes and their dependence on the crystal structures
Authors: Cohen M. D. , Ludmer Z. , Yakhot V. 
Published: July 2007

AbstractThe fluorescence properties of a number of crystalline anthracenes are described. It is found that in excimer‐emitting crystals the energy of the emission is shifted by change in temperature much more strongly in infinite‐stack structures than in structures based on pair‐wise packing. A theoretical treatment is given of the general problem of the excimer emission from a crystal, and is applied to the anthracenes. This theory shows that the sensitivity to temperature for high temperatures is determined by the ratio of the frequencies of intra‐pair vibrations in ground and excited states of the particular material. An interpretation of the difference in this ratio for stack and pair structures is given, and some predictions based on this interpretation are given and tested. It is confirmed that structures in which molecular overlap is small give rise to monomer emission.
Elastic interaction of point defects in isotropic and anisotropic cubic media
Authors: Schaefer H. E. , Kronmüller H. 
Published: July 2007

AbstractUsing the Green's tensor function as the solution of the elastic equations for isotropic and anisotropic cubic media the elastic interaction energy is calculated for pairs of defects which have isotropic, tetragonal, or orthorhombic symmetry. Special attention is given to the interaction of a one‐dimensionally migrating interstitial, in crowdion configuration, with other defects. The differences of the interaction in elastically isotropic and anisotropic materials, the influence of defect anisotropy on the interaction potential, and the relation of these calculations to experimental results are discussed.
Binding energies and wave functions of wannier excitons in uniaxial crystals — a modified perturbation approach. I. theory
Authors: Gerlach B. , Pollmann J. 
Published: July 2007

AbstractThe effective mass Hamiltonian for excitons in uniaxial crystals is discussed by means of a modified perturbation approach. This approximation scheme gives upper limits for the exact energies; the validity of the approach is tested by deriving lower limits for the exact energies. The spacing of the two limits is shown to be satisfactorily small in a wide range of the anisotropy parameter. This parameter free approach leads to energies, which show good agreement with the results of involved variational calculations. In addition analytical expressions are obtained for the wave functions, which are easy to handle and can be used in more complex situations e.g. to include the description of external field influences.
Optical absorption spectrum of CoIII in LaCoO3
Authors: Marx R. , Happ H. 
Published: July 2007

AbstractThe optical spectrum of Co111 in LaCoO3 has been investigated between 6500 and 34000 cm−1. The observed crystal field splittings are explained by a crystal potential of cubic and axial symmetry. The cubic and axial ligand field parameters and the Raccah parameters describing the electron interaction are determined and their consequences with respect to the magnetic properties of LaCoO3 are discussed. A critical summary of the existing theories concerning the absorption spectra of 3d electrons of transition metals in cubic and axial fields will be given.
An analysis of models for the ionic conductivity of silver chloride
Authors: Coerish J. , Jacobs P. W. M. 
Published: July 2007

AbstractThe high‐temperature conductivity of pure AgCl has been re‐examined with a view to establishing more precisely the mobility parameters for non‐collinear interstitialcy motion of Ag+ interstitials. The possible roles of direct interstitial jumps, Schottky defects, and temperature dependent activation energies has been assessed. Fomulae are given for the activity coefficients of interstitials and vacancies evaluated to O(x2) in an approximation that uses a sphericalized Brillouin zone and inlcudes only the cycle sum contributions. These activity coefficients are compared with those evaluated from the Debye‐Hückel formula and their effect on the defect parameters obtained from conductivity data is assessed.
Band structure of solid o‐H2 with the molecular tight‐binding and OPW method
Authors: Parravicini G. Pastori , Villa I. , Vittori M. 
Published: July 2007

AbstractThe band structure of f.c.c. solid hydrogen is computed using the molecular tight‐binding method for the valence band and the molecular OPW method for the conduction bands. The direct energy gap is found to be 15.1 eV and corresponds to the allowed transition L → L. The pressure dependence of relevant states is obtained and it is shown that the energy gap decreases with pressure. Some features of the far vacuum ultraviolet excitation spectrum are qualitatively interpreted.
An investigation of the structure of Cu‐H centers in ZnO by EPR
Authors: Zwingel D. 
Published: July 2007

AbstractIn ZnO single crystals, doped both with hydrogen and copper, three new EPR spectra are reported which are assigned to different CuH complexes. It is found that an OH group is formed next to a substitutionally incorporated Cu2+ ion (or pairs thereof). The paramagnetic properties of these centers are markedly different from the known isolated ZnO :Cu‐center and may be described rather well by simple crystal field theory of a 3d9 ion.
The dynamical conductivity of electrons in semiconductors assuming scattering by dislocations
Authors: Gerlach E. , Rautenberg M. 
Published: July 2007

AbstractUsing a method, which is based on the equivalence of energy loss and Joule heat, the dynamical conductivity of semiconductors is calculated. Scattering by dislocations is assumed, which are described by a simple monopole and dipole line model. The theory is applied to Te for frequencies 107 to 1014 Hz (10−7 to 1 eV) and for temperatures T = 10, 20, and 30 K.
Antiferromagnetic resonance in NIO:Co2+ and NIO:Fe2+
Authors: Ph. Lau C. R. Becker , Geick R. , Wagner V. 
Published: July 2007

AbstractThe antiferromagnetic resonance (AFMR) in NiO doped with either Fe2+ or Co2+ was studied at liquid helium temperatures in the far infrared. A strong frequency shift of the AFMR line was observed in Co2+‐doped crystals. In the case of the Fe2+‐doped crystals, this shift was much smaller. In addition, a second absorption line was found at larger Co2+ concentrations (5% to 7%), the nature of which has not yet definitely been established. A simple model calculation which primarily employs the single ion anisotropies of the Co2+ and Fe2+ ions was performed for a qualitative interpretation of the experimental results.
Cyclotron resonance of electrons in semimetallic bismuth‐antimony alloys
Authors: Herrmann R. , Brbune W. , Kuka G. 
Published: July 2007

AbstractThe cyclotron resonance of electrons in semimetallic BiSb alloys is investigated within a range of 0 to 4 at % antimony at 35 GHz in three crystallographic planes. A nonlinear dependence of the cyclotron masses on the antimony concentration (x at %) is found. The analysis of spectra indicates limiting‐point resonances being associated with the cyclotron wave propagation.
A theory of DC‐hopping conductivity in a disordered one‐dimensional system accounting for electrical fields of arbitrary strength
Authors: Bottger H. , Bryksin V. V. 
Published: July 2007

AbstractThe current‐voltage characteristics are investigated for the dc‐hopping processes in disordered one‐dimensional systems with nearest‐neighbour hopping only. It is shown that in such systems strong local fields can give rise to a nonlinear current‐voltage dependence at much lower external fields than in a corresponding ordered system. Qualitatively similar results may also be expected for three‐dimensional systems.
Lattice dynamics of rare‐gas solids by Kihara's potential: I. Phonon spectra
Authors: Agrawal T. N. , Gupta R. K. , Gupta G. L. 
Published: July 2007

AbstractThe applicability of Kihara's potential function to rare‐gas solids has been investigated by studying their lattice dynamics. The intermolecular potential parameters are determined from the experimental sublimation energy and lattice spacing extrapolated to 0 °K, taking into account the zero point energy. These parameters are used to compute the theoretical phonon spectra for the solidified rare gases neon, argon, krypton, and xenon. The theoretical results are found to compare well with available experimental data.
The electronic structure and phase diagrams of binary alloys with complex lattices: I. The application of static concentration waves and pseudopotential methods for calculating the phase diagrams
Authors: Zhorovkov M. F. , Fuks D. L. , Panin V. E. 
Published: July 2007

AbstractIt is shown that the structures of the ordered phases in binary alloys with complex Ising lattice (made up by the α‐Bravais lattices displaced with respect to each other) can be determined theoretically by means of the static concentration wave (s.c.w.) method and pseudopotential theory. The expression which gives the relationship between the phenomenological parameters of the s.c.w. method and the energy‐wavenumber characteristicof thepseudopotential theory is obtained. The superstructures which may be stable with respect to the formation of an antiphase boundary structure is obtained for the hexagonal close‐packed lattice.
Tight‐binding calculations of the valence bands of diamond and zincblende crystals
Authors: Chadi D. J. , Cohen M. L. 
Published: July 2007

AbstractUsing the tight‐binding method, the valence band structures and densities of states for C, Si, Ge, GaAs, and ZnSe are calculated. Very good agreement is obtained with other calculations when all nearest‐ and one second‐nearest‐neighbor interactions are included. The effects of the various interactions on the density of states are discussed.
Radio‐frequency size effect in bismuth
Authors: Müller H.‐U. , Hess S. , Herrmann R. , Scholz H. 
Published: July 2007

AbstractThe anisotropy of the momentum of the Fermi surface of electrons has been investigated by the radio‐frequency size effect. By variation the polarization of the radio‐frequency field it is possible to determine completely the anisotropy of the momentum in the trigonal and binary planes. The shape of the Fermi surface in the binary plane is shown to be different from the ellipsoidal one and not symmetric to the axis.
Exchange integral determination in Co3O4
Authors: Scheerlinck D. , Hautecler S. , Wegener W. 
Published: July 2007

AbstractThe energy distributions of neutrons scattered by Co3O4 in its paramagnetic state have been measured by means of a time‐of‐flight technique. In this normal spinel with only A‐A interactions, the JAA exchange integral has been derived from the second moment of these energy distributions. The result, JAA/kB = (7.27 ± 0.25) K, has been compared with values deduced from an analysis of the macroscopic magnetic data.
Dispersion relation for surface wannier excitons
Authors: Rimbey P. R. 
Published: July 2007

AbstractThe surface exciton dispersion relation is derived for a spatially dispersive medium including the additional boundary condition Px(0+) = 0. The dispersion is complex for long‐wavelength P‐polarized light in the absence of phenomenological damping suggesting surface excitons exist as critically damped wavepackets.
Effect of the anisotropy of atomic motions on Mössbauer spectra of polycrystals
Authors: Goldanskii V. I. , Karyagin S. V. 
Published: July 2007

AbstractExamples of anisotropic motions (vibrations, diffusion, eddy flows) are given which lead to the dependence of the shape of Mossbauer spectra on the relative orientation of the system studied (a part of a monocrystal) and the direction of observation of γ;‐rays. The anisotropy of continuous diffusion in polycrystals is found to result in different broadenings of the π and σ components. The jump diffusion is found to induce a virtually equal broadening of the π and σ components. The line shape in this case is non‐Lorentzian. Study of line shapes can give essential information on the diffusion mechanism.