bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unified study of metals on pseudopotential theory: Lead
Authors: Sen D. , Sarkar S. K. 
Published: July 2007

AbstractA comprehensive unified study of lattice‐mechanical and electronic properties of lead using the Heine‐Abarenkov model potential and Harrison's two‐parameter model potential is made. Screening functions proposed by Taylor and by Vashishta and Singwi, coupled with the two pseudopotentials are used in order to make a comparative study of their effectiveness. Properties studied include cohesive energy, equilibrium lattice parameter, second‐order elastic constants, pressure derivatives of second‐order elastic constants, equation of state (at T = 0), and phonon dispersion relation of crystalline lead and the resistivity and thermoelectric power of the liquid metal. Inspite of its excellence in reproducing one set of properties, Harrison's potential is found to be inadequate for a unified study. The Heine‐Abarenkov potential, on the other hand, is found to be better suited for the purpose. The liquid metal resistivity, however, is found to be much lower than the experimental value. In fact, it is pointed out that this is a common feature of all unified studies with pseudopotentials.
Group‐theoretical study of light‐induced electron‐spin polarization at the Γ‐point of cubic crystals
Authors: Wöhlecke M. , Borstel G. 
Published: July 2007

AbstractSelection rules are calculated for the excitation of light‐induced spin‐polarized electrons at the center of the Brillouin zone of cubic crystals. The derivation of such rules is based on an application of the generalized Wigner‐Eckart theorem and tabulated coupling coefficients for unitary point groups. For almost all transitions a net electron‐spin polarization less than 50% is achieved. This is mainly due to the existence of bases which are linear combinations of spin‐up and spin‐down states. Tables are presented for the groups Oh, O, and Td. The connection of the results for Γ to those of the high‐symmetry lines is discussed.
Theoretical description of planar channeling process at small depths
Authors: Kührt E. , Wedell R. 
Published: July 2007

AbstractA model for the description of planar channeling processes on the basis of the solution of the Fokker‐Planck equation is developped. It is applied for the calculation of the backscattering yield of protons and He‐ions in planar channels of several single crystals. The results are compared with recent measurements.
Green functions, power spectra, and Raman scattering of thin film polaritons
Authors: Oliveira F. A. , Cottam M. G. , Tilley D. R. 
Published: July 2007

AbstractLinear response theory is used to evaluate Green functions for the electric field fluctuations in a general three‐layer system. The Green functions provide a description of the bulk polaritons, surface polaritons, and guided bulk polaritons. Particular consideration is given to polaritons arising from coupling of photons to optical phonons. The results are illustrated with dispersion curves and power spectra for different materials and geometries. The theory of light scattering by the excitations is then presented. A general formalism is developed to express the scattering cross‐section in terms of the Green functions. The full result contains a description of light scattering from bulk polaritons, guided bulk polaritons, and surface polaritons. However, the discussion is concentrated mainly on scattering from the localised surface modes.
Ellipticity effects in spin‐wave spectrum of thin magnetic films
Authors: Duda A. 
Published: July 2007

AbstractThe microscopic and resonance properties of the elliptic spin‐wave polarization are analysed for a Heisenberg ferromagnet thin film with an internal dipolar anisotropy and uniaxial surface anisotropy. The general case of arbitrary oriented external magnetic field is considered. It is found that the bulk and surface sources of the ellipticity influence distinctly the resonance spectrum of spin waves.
Compaison of the s band structure of face centred cubic and hexagonal close packed solids. I. The common zone approach
Authors: Betteridge G. P. 
Published: July 2007

AbstractThe relationship between electron energy levels and atomic environment is investigated by comparing the band structures of the two closely related structures, f.c.c. and h.c.p. Analytical expressions for the energy bands are obtained for a single s electron per lattice site in each structure, using a simple tight binding Hamiltonian incorporating interactions out to third nearest neighbours. A procedure is developed whereby both band structures are expressed in the same zone, thus enabling direct k space comparison. When viewed in this way the band structures for both crystal structures are shown to be very similar, the main deviations occurring over the boundary faces of this common zone.
Estimation of Covalency Effects in the Optical Spectra of Crystals Containing Iron Group Ions (II)
Authors: Kustov E. F. , Uskova L. I. , Klinchikov S. A. 
Published: July 2007

AbstractIn the first part of the paper the general matrices were derived for taking into account covalency effects. However, the solution of these matrices in an analytical form is difficult even for cluster with two electrons (holes). In this paper the covalency effects are taken into account and the parameters σ, Dq, E0, λe, λt, for some compounds with ions Ni2+, Cr2+, and Co2+ are calculated, using the restandardization of state functions of the central ion.
Water Vibrations in Ferroelectric K4Fe(CN)6 · 3 H2O
Authors: Anachkova E. , Ratajczak H. , Savatinova I. 
Published: July 2007

AbstractRaman and infrared studies are performed of water vibrations of KFCT crystal in the region of 300 to 1700 cm−1. Spectral changes are followed in the temperature interval from room temperature down to 30 K. Special attention is paid to the band at 325 cm−1 whose temperature behaviour is typical for hindered rotation modes. Its frequency change is consistent with the change of the potential barrier restricting the water motion which was reported before.
Theoretical Analysis of Some Ground State and Optical Properties of Impurity F Centers
Authors: Harker A. H. , Vail J. M. 
Published: July 2007

AbstractComparisons with experimental data are used to assess calculations on F‐type centers, based on an approximate pseudopotential model, using flexible symmetry‐adapted variational wave functions. Moderate success is obtained for optical absorption of the linear FB center in KCI:Na and RbCI:Na, and for the triangular FB center in KCI:Na. Satisfactory results for nearest‐neighbor isotropic hyperfine interactions of the FA center ground state in KBr:Li are obtained only from point‐ion wave functions, although to describe adequately optical absorption of the F and FA(Li) centers in KBr requires that the ion‐size correction must be included. Luminescence from the type II FA center in KCI:Li is also found to require the point‐ion approximation, including angular momentum components l > 1.
Energy Levels of Intrinsic and Extrinsic Stacking Faults in Silicon
Authors: Marklund S. 
Published: July 2007

AbstractThe electronic interface states of ideal intrinsic and extrinsic stacking faults are calculated using an empirical pseudopotential. The results show two occupied bands above the valence band top (≈︁ Ev + 0.1 eV) for both the faults. No localised states near the conduction band are found which contradicts experimental results for the extrinsic faults interpreted as levels at ≈︁ Ec − 0.1 eV.
Static and Dynamic Structure Factors of Classical Plasma in Weak and Intermediate Couplings
Authors: Dubey G. S. , Chaturvedi D. K. 
Published: July 2007

AbstractUsing the sum rule arguments a self‐consistent scheme is utilized to calculate the short‐range correlations in classical one‐component plasma. The results are used to obtain the static and dynamic structure factors in a unified framework, which are found to be in reasonably good agreement with the available molecular dynamics data in the domain of weak and intermediate couplings ( Γ < 20). The longwavelength limit, where thermodynamic functions are related to the static structure factor, is also analyzed.
The Theory of Thermal Dechanneling from Axial Channels
Authors: Rozhkov V. V. , Rutkevich P. B. 
Published: July 2007

AbstractOn the basis of a thorough analysis of the stochastic proporties of particle motion in axial channels with thermally vibrating atoms the Fokker‐Planck equation for the distribution function of channeled particles over transverse motion energy is obtained. A random parametric effect of the thermal vibrations on the transverse motion of channeled particles is discovered. Analytical expressions for the distribution function over the transverse energy, the dechanneling function, and the integral penetration distribution foi particles injected into a crystal under channeling conditions are obtained.
EPR Investigations of a Structural Phase Change in Lead Phosphate
Authors: Razeghi M. 
Published: July 2007

AbstractThe temperature dependence of the EPR line width of the Mn2+ and Gd3+ in Pb3(PO4)2 is investigated from ‐270 to 500 °C. At the first‐order ferroelastic transition point (180 °C), an abrupt change in the fine‐structure splitting as well as in the resonance line width is observed. Various contributions to fine structure D and E parameters of Mn2+ and Gd3+ are computed, using a point‐multipole model. For temperatures near to Tc the correlation time of the fluctuations is estimated to be greater than 10−9.
On the Lifetime of Excited States in One‐Dimensional Disordered Systems
Authors: Esser B. 
Published: July 2007

AbstractA macroscopic system realizing an ensemble of chain‐like recombination paths involving localized electron states is considered. The recombination process of a carrier occurring in a given chain is formulated in terms of a Markov process with absorbing state. An expression for the mean lifetime of a carrier in a chain taking account of the energy scatter of the electron states is derived. Using this expression and a density of states model the temperature dependence of the lifetime may be calculated explicitly.
Magnetic Phases of Strongly Correlated Electrons in a Nearly Half‐Filled Narrow Band
Authors: Spalek J. , Oleá A. M. , Chao K. A. 
Published: July 2007

AbstractA canonical perturbation technique is used to investigate a nearly half‐filled nondegenerate generalized Hubbard Hamiltonian a t the strong intraatomic correlation limit. Quasiparticle state and the total energy for various magnetic orderings are obtained using the Green function method with the moment‐conserving decoupling scheme. A ground state magnetic phase diagram with antiferromagnetic, ferromagnetic, and mixed phases is derived and compared to existing results. The dependence of the critical W/U ratio for metal‐nonmetal transition on the interatomic exchange is estimated.
Nonlinear Energy Transport of Radiation in Dielectrics Due to Virtual Biexciton Formation
Authors: Schmitt‐Rink S. , Haug H. 
Published: July 2007

AbstractThe intensity‐dependent dielectric function is calculated from the photon self‐energy taking into account the two‐photon generation and autoionization (Fano effect) of biexcitons. The polariton density is determined self‐consistently as a function of the intensity, frequency, and space using the concept of the energy transport velocity. Two‐photon absorption spectra are calculated which are in good agreement with recent experiments.
On Elastic Properties of Dihedral Edge Dislocations
Authors: Bonnet R. 
Published: July 2007

AbstractFirstly, the elastic displacement and stress fields of an edge dislocation located at the corner of a dihedral interface separating two media + and ‐ are discussed using isotropic elasticity. A fully analytical solution is derived and particular examples are calculated for the shear stress field when the ratio of both shear moduli μ+/μ− is 2 and 1/2, and the dihedral angle is 60°. Secondly, an example which illustrates the shear stress field of a dihedral edge dislocation at the corner of two {112}facets of a twin boundary in gold is presented using anisotropic elasticity.
Hole Effective Masses in CuInSe2
Authors: Neumann H. , Kissinger W. , Sobotta H. , Riede V. , Kühn G. 
Published: July 2007

AbstractOptical transmittance and reflectance spectra are measured in p‐type CuInSeZ single crystals at 100 and 300 K in the photon energy range from 0.03 to about 1.0 eV. At hv = 0.07 to 0.70 eV the absorption is governed by intervalence band transitions. Assuming spherical parabolic energy dispersion relations for all the three valence bands, the effective masses of the heavy hole, light hole, and split‐off bands are determined to mhh = 0.71m0, m1h = 0.092m0, and msh = 0.085m0, respectively.
Vacancy‐Induced and Two‐Phonon Raman Scattering in ZrCx, NbCx, HfCx, and TaCx
Authors: Wipf H. , Klein M. V. , Williams W. S. 
Published: July 2007

AbstractRaman scattering is studied in the substoichiometric transition metal carbides. The carbon vacancies in these cubic solids induce a one‐phonon spectrum that essentially mirrors the phonon density of states. The superconducting group Vb carbides NbC0.98 and TaC0.99 have one‐phonon Raman spectra that show characteristic phonon softening. Strong A + A and O + A two‐phonon peaks are also seen. In NbC0.76, which has a low Tc, the one‐phonon peaks harden, and the two‐phonon intensities weaken. Mechanical polishing of NbC0.98 and TaC0.99 reduces two‐phonon scattering and hardens and broadens the one‐phonon spectra. The non‐superconducting adjacent group IVb carbides ZrC0.96, ZrC0.87, and HfC0.99 have higher‐frequency one‐phonon peaks and no two‐phonon features.
Mössbauer Radiation Diffraction in Deformed Crystals
Authors: Baryshevskii V. G. , Skadorov V. V. 
Published: July 2007

AbstractThe dynamical theory of the diffraction of a spatially inhomogeneous field of Mössbauer γ‐quanta by perfect and deformed crystals is considered. The equations describing the dynamical diffraction of Mössbauer γ‐quanta is considered. It is shown that it is possible to enhance the Mössbauer radiation intensity by three orders as compared to the incident radiation intensity.
The Theory of the Superconductive Phase in Rare Earth Metal Compounds
Authors: Panina L. V. , Savchenko M. A. , Stephanovich A. V. 
Published: July 2007

AbstractThe microscopic theory of the superconductive phase in rare earth metal compounds is constructe by the contour averages mathematical method. It is shown that in the superconductive phase thd effect of exchange intensification occurs and increase of superconductive phase transition tempere ature is possible.
Random Bond Ising Model in Self‐Avoiding Walk Approximation
Authors: Medvedev M. V. , Sadovskii M. V. 
Published: July 2007

AbstractFree energy of random bond Ising model is analysed by high‐temperature expansion in self‐avoiding walk approximation. Conditions of instability of the paramagnetic state are determined through the convergence criterion of the random high‐temperature series. Critical concentrations for the loss of the long‐range magnetic order are determined for different 2d and 3d lattices.
Crystal‐Field Analysis of Electronic Raman Scattering Data in YbAG and YbGG
Authors: Nekvasil V. 
Published: July 2007

AbstractThe relative Raman intensities associated with various electronic transitions are used simultaneously with the usually considered energy levels and g‐values for determination of the phenomenological crystal‐field parameters in YbAG and YbGG. The best‐fit parameters reproduce well all the available data but their values do not agree with the superposition model of the crystal field. It is concluded that the earlier crystal‐field calculation for Yb3+:YAG is impaired by the misinterpretation of the optical data.
Semiempirical Calculations of Defect Properties in LiF Crystal. II. Electron and Hole Centres and Their Recombination
Authors: Kotomin E. A. , Shluger A. L. 
Published: July 2007

AbstractThe electronic structure of F, H, Vk centres in a LiF crystal is calculated using the INDO semiempirical method. Use of both, the modified calculating scheme and earlier derived parameters permit to reproduce quite well optical absorption energies for hole centres and confirm their model of F molecular ion in a crystal. The locations of defect levels with respect to the band edges of a perfect LiF crystal are discussed. The calculations of pairs of nearest F–H, F–Vk centres predict energies of their radiative tunneling recombination of about 1 and 1.4 eV, respectively.
The Spectrum of an Intermediate Polaron and Its Bound States with Phonons at Strong Coupling
Authors: Gogolin A. A. 
Published: July 2007

AbstractThe spectrum of intermediate‐radius polaron at strong coupling g ≫ 1 is evaluated with the help of a new diagram technique. The bound states of the polaron with a large number of phonons N = 2g2 are found. In the case of an exciton, these states give rise to additional strong peaks in the absorption and luminescence spectra.
Effect of Fluctuations of the Coordination Number on Some Properties of Amorphous Ferromagnets
Authors: Bobák A. 
Published: July 2007

AbstractThe classical‐spin Bethe‐Peierls‐Weiss method is used to determine the Curie temperature and the paramagnetic susceptibility of amorphous ferromagnets. Due to the structure fluctuations of the coordination number a decrease of the Curie temperature and the paramagnetic susceptibility is found in comparison with the corresponding crystalline case. The same formalism is employed to study the chemical disorder introduced by substituting magnetic impurities in a non‐magnetic amorphous host. It is shown that the critical concentration of magnetic atoms for the appearance of long‐range magnetic order is increased by fluctuations of the coordination number.
Polarized Luminescence of Lead Ions Associated with Interstitial Radiation Defects in KCl:PbCl2 Crsytals
Authors: Egemberdiev Zh. , Zazubovich S. , Nagirnyi V. 
Published: July 2007

AbstractTwo types of lead ion and interstitial chlorine atom associates (Hz(Pb2+) centres) are found and investigated by optical methods in X‐irradiated KCl:PbCl2 crystals. The polarized 3.35 and 1.8 eV emission of these centres and the absorption bands near 5.55 and 4.4 eV are caused by electronic transitions in the Pb2+ ion perturbed by Cl molecular ion, which occupies a cation vacancy and an anion site. The broad absorption band at 3.7 eV is due to the transitions in the Cl ion perturbed by Pb2+. Using the ESR data obtained by Schoemaker et al. it is concluded that the centres with 3.35 and 1.8 eV emission are interstitial chlorine atoms trapped by Pb2+ ions associated with the nearest neighbouring (Hz[110](Pb2+) centres) and with the next nearest neighbouring (Hz[100](Pb2+) centres) cation vacancies, respectively. Lead ion and Cl molecular ion associates (V2z(Pb2+) centres) are found. The polarized 3.05 eV emission and the 4.3 eV absorption band of these centres are caused by the electronic transitions in Pb2+ ions perturbed by Cl. The broad 5.27 eV absorption band is due to the electronic transitions in the Cl ions perturbed by Pb2+. It is assumed that the V2z(Pb2+) centre may be represented as a Cl molecular ion which occupies two anion and one cation sites and is associated with a Pb2+ ion located (according to Itoh et al.) at a face‐centred position as well as with an interstitial chlorine ion and cation vacancy.
From Band to Hopping Diffusion of Excitons and Charge Carriers in Molecular Crystals. II. Results for Local and Weak Nonlocal Electron‐Phonon Coupling
Authors: Čápek V. , Munn R. W. 
Published: July 2007

AbstractPrevious results giving the diffusion coefficient for an exciton or charge carrier in a perfect molecular crystal in both the band and the hopping regime, and interpolating between regimes, are evaluated with and without nonlocal electron‐phonon coupling to second order. Nonlocal coupling produces an extra contribution to the hopping rate; it may increase or decrease the usual scattering rate, depending on the relative signs of local and nonlocal coupling, but changes the transfer rate in the opposite direction through the phonon displacements in the polaron states produced by local coupling. Increasing the temperature decreases the importance of nonlocal coupling in the band regime but increases it in the hopping regime. The significance of these effects depends on the detailed coupling model. The enhanced hopping rate agrees with previous published work.
The CrK Series X‐Ray Emission Spectra
Authors: Sørum H. , Weng O. M. , Bremer J. 
Published: July 2007

AbstractThe electron‐excited CrK series X‐ray spectra are investigated by means of curved crystal spectrometry, permitting at the same time high intensity and resolution. No directly observable fine structures are found for α1,2 and β1, 3. Low‐energy satellites as well as weak high‐energy satellites are, however, found both for α1,2 and β1,3. A low‐energy satellite may be present also for β5. The high‐energy satellites for the α‐doublet are most probably due to a spectator vacancy in the M‐level and/or in the valence band V, corresponding to the transitions KM → LM, KV → LV, respectively. Similarly the β1,3‐structure may contain contributions from the transitions KM → LM and/or KV → MV. In addition to the structure caused by interaction between the final‐state hole and the unfilled 3d‐level the radiative Auger effects K → LV, K → MV, and K → VV are probably present at the low‐energy side of the lines. The FWHM value for α1 is (1.90 ± 0.05), for α2 (2.60 ± 0.05), for β1,3 (2.68 ± 0.05), and for β5 (4.9 ± 0.1) eV. The spin‐orbit split between the 3p3/2 and 3p1/2 levels is measured for the first time to be 0.74 eV for Cr, a value which is thus considerably less than the theoretical value of 1.06 eV.
An Expansion Technique for Evaluating Densities of States and Related Integrals
Authors: Pisani C. 
Published: July 2007

AbstractA calculation technique for the densities of states is presented which is based on the expansion of ϱ(ϵ) in a series of orthogonal functions in the band interval. Formulae are proposed for a simple evaluation of the expansion coefficients. When the eigenvalue and eigenvector dependence on κ is expressed as a linear combination of lattice waves and spherical Legendre polynomials are used as orthogonal set, the expansion coefficients are calculated exactly. The properties of convergence and some numerical aspects are discussed with reference to cubic lattices in the tight binding approximation.
Lindeman's Melting Law and the Effect of Pressure on the Melting Point of Si and Ge
Authors: Soma T. , Matsuo H. 
Published: July 2007

AbstractUsing the volume dependence of the mean‐square displacement, the pressure effect on the melting temperature of Si and Ge is studied by Lindeman's melting law. The melting curve obtained decreases as function of the compressed volume, and is qualitatively in agreement with the observed tendency for Si and Ge.
Transitions in Fast Ionic Conductors
Authors: Gluck P. 
Published: July 2007

AbstractA two state model, based on different degrees of ionicity in the β and α phase, is used as a basis for discussion of the phase transition and dc conductivity in AgI‐type ionic conductors. A decrease (softening) in the frequency of anion oscillations is capable of accounting both for the transition from low to high ionicity (β → α) states, and for the increase in dc conductivity by several orders of magnitude.
Thermodynamic Properties of Liquid Alkali Metals and Their Equiatomic Alloys
Authors: Mishra S. C. , Srivastava P. L. 
Published: July 2007

AbstractGibbs‐Bogolyubov variational technique is used to study ‘internal energy’ and ‘entropy’ of liquid alkali metals as well as ‘heat of mixing’ and ‘entropy of mixing’ of their equiatomic alloys. Shaw and Ashcroft forms of model potentials with Vashistha, Singwi and Shaw forms of exchange and correlation functions are used for the calculations of the said properties.