bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photo‐chemical reaction and photo‐induced polarization studies in sulphur‐doped potassium bromide
Authors: Praksh J. 
Published: July 2007

AbstractThe absorption bands of S2−‐anion vacancy dipoles in KBr lie in the ultraviolet range. Irradiation in the short‐wavelength absorption bands results in a photo‐chemical reaction. It is observed that the irradiation in the presence of an electric field in the long‐wavelength absorption band creates a situation in which more dipoles are aligned along the electric field direction. Irradiation in absence of the electric field in the long‐wavelength absorption band is found to destroy the frozen‐in alignment of polarized dipoles.
Effects of a transition layer on slab polaritons
Authors: Wendler L. 
Published: July 2007

AbstractDispersion relations are derived for polaritons in a dielectric slab, coated with a transition layer (thickness 20 to 150 Å), on a substrate. If \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document} 1(ω) is the dielectric function of the transition layer a splitting of the dispersion curves occurs for resonances of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω ⟂) = ∞ and \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω∥︁) = 0 in the case of p‐polarized polaritons. In the case of s‐polarized polaritons the splitting is obtained only for resonances of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω ⟂) = ∞.
Anisotropy of transport properties due to direction‐dependent band nonparabolicity
Authors: Stordeur M. , Langhammer H. T. 
Published: July 2007

AbstractIn addition to two‐band conduction or the action of an anisotropic‐mixed scattering mechanism a further possibility is proposed for the interpretation of the anisotropy of the Seebeck coefficient, the Hall coefficient, and the Lorenz number of semiconducting crystals with noncubic symmetry. In the band model a nonparabolicity is considered which depends on the crystal direction. For acoustic mode scattering the expected anisotropy of these effects is calculated in dependence on the reduced Fermi level with the nonparabolicity as the parameter. The numerical results show that in contrast to the isotropic nonparabolicity the model used here predicts distinct anisotropies.
Ground state and effective field distribution of ising and heisenberg disordered antiferromagnets
Authors: Petrakovskii G. A. , Aplesnin S. S. 
Published: July 2007

AbstractGround state of disordered antiferromagnets (AFM) is investigated by the Monte Carlo method for the case of simple cubic lattices of Ising and classical Heisenberg models. The sublattice magnetization and spin—spin correlation function and phase boundary between AFM and spin glass are calculated at various values of concentration v of the ferromagnetic I‐bonds and the parameter λ == J/|K| (K < 0, antiferromagnetic bonds). The upper bound of degeneracy of random AFM is evaluated and the distribution of effective fields is presented.
Phonon Relaxation Due to Anharmonism and Central Peak in Structural Phase Transitions I. Soft Optic Modes and Acoustic Phonons in Cubic Crystals
Authors: Kashcheev V. N. 
Published: July 2007

AbstractIn the mode–mode coupling approximation the critical exponente (CE) are calculated for the damping and frequency shift of soft optic modes and acoustic phonons at the structural transition point for crystals with dimensions d = 1, 2, 3. The CE are traced back to the anharmonic interaction of phonons taking into account the intrinsic dynamic central peak of any nature. Anharmonisms of all order are considered.
EXAFS Study of Crystalline Cu, Ni, and Fe
Authors: Ershov N. V. , Babanov Yu. A. , Galakhov V. R. 
Published: July 2007

AbstractThe X‐ray absorption K‐spectra of copper, nickel, and iron are registered at nitrogen and room temperatures using synchrotron radiation. The experimental conditions and the experimental data of the preliminary‐processing procedure are described. The radial atomic distribution functions of copper, nickel, and iron are obtained from the analysis of the extended X‐ray absorption fine structure by the regularization method.
Decomposition of SiOx Films Due to Internal Stress
Authors: Hübner K. , Shendrik A. V. , Praulinsh A. M. 
Published: July 2007

AbstractResults of optical absorption, reflectance, and ESR measurements are presented, which demonstrate that SiOx films characterized originally by a random‐bonding structure reveal after aging at room temperature a partial decomposition to Si and SiO2, i.e. a transition to a mixture structure. This decomposition is explained with the help of a model for the internal mechanical stress of SiOx films due to the large difference between the expansion coefficients of their Si and SiO2 constituents.
Theorie des durch das äußere Magnetfeld induzierten Jahn‐Teller‐Effektes in orthorhombischen J = 1‐Paramagneten
Authors: Ulner J. 
Published: July 2007

AbstractEs wird eine Theorie des durch das äußere Magnetfeld induzierten Jahn‐Teller‐Effektes in orthorhombischen J = 1‐Paramagneten formuliert, die die Rotationsinvarianz der magnetoelastischen Wechselwirkungen mit einbezieht. Mit Hilfe einer Greenfunktionsmethode, die die Eigenschaften des Gesamtdrehimpulses exakt berücksichtigt, werden die elementaren Anregungen des Systems ermittelt. Es wird die Temperatur‐ und Magnetfeldabhängigkeit der Schallgeschwindigkeiten bestimmt und diskutiert. Bei Abwesenheit der Rotationsinvarianz der magnetoelastischen Wechselwirkungen korrespondieren die untersuchten Schallgeschwindigkeiten mit den elastischen Konstanten c55 und c66.
Incomplete Gamma Functions and Lattice Sums for B.C.C. Structures
Authors: Gupta K. C. , Agrawal R. M. , Rathore R. P. S. 
Published: July 2007

AbstractCertain wave vector dependent lattice sums which extend over the entire lattice are computed for b.c.c. structures by the method of Born and Bradburn. These lattice sums are of general importance in the studies of some thermodynamical properties of lattices particularly the vibrational studies. All the needed values of incomplete gamma functions are also presented since they are required in the evaluation of the lattice sums in general.
Quasi‐Classical Quantization for Potentials with an Infinite Surface Barrier. Subbands in Inversion Layers
Authors: Paasch G. , Fiedler T. , Klář M. , Bartoš I. 
Published: July 2007

AbstractFor potentials with a high surface barrier, quasi‐classical quantization schemes are investigated. WKB and other previous approximations provide good results for the lower eigenvalues in special cases only. Here a modified local density approximation is used for the calculation of the density of states. From the integral density of states a quantization expression is derived where the ground state constant depends explicitly on the shape of the potential. It yields the whole eigenvalue spectrum very precisely for quite different potentials with surface barrier. The application to subband energies in inversion layers is discussed.
Some remarks on the theory of the dielectric response of crystals and on the lorentz‐lorenz formula
Authors: Fiorino E. , Del Sole K. 
Published: July 2007

AbstractAn investigation is made of the macroscopic dielectric function of a model insulator including local field effects and treating exchange by (i) the many‐body perturbation technique, (ii) the mean field, and (iii) excitonic approximations. The different methods yield similar results, showing the reliability of approximations (ii) and (ii) in most cases. Also the validity of the Lorentz‐Lorenz formula is discussed, showing that it is always valid in cubic crystals, if the “atomic” polarizability is suitably defined as the limit of the crystal polarizability for vanishing dipole—dipole interaction.
Magneto‐optical properties of RbMnF3 in the paramagnetic state
Authors: Malakhovskii A. V. , Morozova T. P. , Yuzvak V. I. 
Published: July 2007

AbstractThe spectrum of the Faraday effect (FE) in the range of 9000 to 37000 cm−1 and its temperature dependence in the range of 90 to 570 K are investigated in RbMnF3. The absorption spectrum in the range of 19000 to 60000 cm−1 and the magnetic circular dichroism spectrum in the range of 19000 to 36000 cm−1 are also obtained at room temperature. FE is decomposed to the following components: A0, the frequency‐independent FE, A, the diamagnetic FE, and C, the temperature‐dependent paramagnetic FE which are found to be commensurate in value with each other. It is shown that: 1. the paramagnetic magneto‐optical activity for the majority of d—d transitions in RbMnF3 is close to the maximum possible one in spite of the lack of orbital moment in the ground state of the Mn2+ ion and due to the spin—orbit interaction in the excited states; 2. C, the term of FE is caused by the highest frequency d—d transition 6A1g → 4T2g(4F) at ω = 51000 cm−1; 3. the diamagnetic FE is caused by the wide band of strong absorption at ω > 60000 cm−1.
Semiempirical theory of shallow short‐range electron traps in silicon in a magnetic field
Authors: Arkhincheev V. E. , Savvinikh S. K. 
Published: July 2007

AbstractA theoretical investigation is made of the intervalley multiplet of electron states localized at short‐range traps in silicon placed in a magnetic field using an approximation of the zero‐short‐range potential. To describe the electron‐impurity interaction the intervalley and intravalley scattering lengths are introduced. They are considered as empirical parameters. It is shown that in crossed constant electric and magnetic fields the electric dipole transitions between multiplet states became available. The formulae describing the dependence of the probability of electric dipole transitions on the field strengths, on their orientation relative to crystallographic axes, and on the polarization of the variable electric field causing transitions, are derived.
Correlation energy from compton scattering and positron annihilation data
Authors: Das G. P. , Chaddah P. 
Published: July 2007

AbstractThe second moments of Compton profiles are used to obtain electronic energies. It is proposed that the second moment of a line‐slit positron annihilation angular correlation curve, in comparison with the second moment of Compton profiles, can yield the correlation energy contribution to the cohesive energy of a material. The need for correcting the PAAC data for the positron enhancement factor and thermalization effects is examined. Numerical estimates of the errors involved are given for sodium and lithium and the possible applicability of the proposal is shown.
Photogalvanic effect in crystal with dislocations
Authors: Efanov A. V. , Entin M. V. 
Published: July 2007

AbstractThe photoelectrical properties of a crystal with identically orientated straight edge dislocations are considered. Such a medium has a preferable direction due to the absence of axial symmetry of the dislocation potential. Hence, the photogalvanic bulk effect may occur. A generalization of the Rhead model is obtained taking into account the deformation potential. Scattering on a dislocation in the classic limit is considered for this case and for the case of an unscreened deformation potential. The tensor of the photogalvanic effect in the ranges of direct interband transitions and of light absorption by free carriers is obtained using the results.
Spectroscopic manifestation of self‐trapping excitons in ionic insulators
Authors: Plekhanov V. G. , Shepelev V. V. , Grinfelds A. U. 
Published: July 2007

AbstractThe luminescence and excitation spectra of free and self‐trapped excitons, whose states are separated by a small potential barrier, are investigated experimentally on an example of NaI and RbI crystals. The height of the self‐trapping barrier is established to be independent of the kinetic energy of an exciton, but it is inversely proportional to its first quantum number. The spectroscopic manifestation of the self‐trapping barrier in the excitation spectra of the steady‐state luminescence of self‐trapped excitons is shown. The value of barrier height obtained experimentally coincides best of all with the value calculated from the theoretical model of the polarizing exciton. The evolution of the luminescence excitation spectra of self‐trapped excitons in a temperature interval 4.2 to 80 K is studied. If the relaxation mechanism of free excitons is reflected in the oscillating structure (the oscillation period is equal to the energy of LO phonon) of luminescence excitation spectra, then the further exciton relaxation along the adiabatic sheet is manifested most directly in the structure of hot luminescence spectra of the self‐trapping excitons.
Domain Wall Stabilization in Crystals with Complicated Magnetic Phase Diagram
Authors: Mitsek A. I. , Sirota D. I. , Kolmakova N. P. 
Published: July 2007

AbstractThe static and dynamic properties of a many‐domain magnetic with a complicated magnetic phase diagram are considered, the domain walls in the magnetic are fastened with plane defects. Near orientational phase transitions the potential pit of a wall may have a fine structure. It results in the anharmonicity of domain wall oscillations, their spectrum depends strongly on the ratio of anisotropy constants. The temperature dependence of the coercive force, magnetic and magnetoelastic hysteresises, and the dynamic susceptibility are discussed.
Polaronic Effects on the Verwey Transition in Fe3O4
Authors: Ihle D. 
Published: July 2007

AbstractOn the basis of a band model for the extra B‐site electrons in Fe3O4 a detailed estimate of the relevant small‐polaron (SP) parameters of Fe3O4 is given taking into account the interatomic Coulomb interaction, the formation of SP due to the interaction with phonons, and the SP correlation. The isotope and pressure effects on the Verwey transition temperature are explained as SP effects.
Evidence of Electromagnetic Quantum 1/f Noise Found in Gold Thin Films
Authors: Kilmer J. , van Vliet C. M. , Bosman G. , van der Ziel A. , Handel P. H. 
Published: July 2007

AbstractPhotonic quantum 1/ƒ noise is identified in Au metal films below the Debye temperature. The low values of the Hooge parameter predicted by Handel's theory (i.e., αtrue ≈ 10−6 to 10−8) are arrived at by realizing that only the fraction ≈ 3kT/2ΔϵF of the total number of carriers is available for scattering at a given temperature.
Activation Energy of Substitutional Defects in Alkali Chlorides
Authors: Bandyopadhyay S. , Neogy C. , Deb S. K. 
Published: July 2007

AbstractBased on a semi‐continuum model, the electrostatic, the polarisation, and the repulsive energy change of a lattice are calculated numerically, as functions of four different types of relaxations for the first fourteen ions of a substitutional defect in the saddle point position in an alkali chloride crystal. It is found that for a particular value of displacement, the total energy change of the lattice is minimum. A study of variation of the angle for the relaxed ions suggests further lowering of the lattice energy corresponding to a particular value of the angular displacement. These results are utilised in calculating the saddle point energy, the migration energy, and the activation energy for the motion of a host ion and a defect ion in NaCl, KCl, and RbCl crystals.
Indirect‐Forbidden Exciton Transitions in AgBr
Authors: Sliwczuk U. , Stolz H. , von Dee Osten W. 
Published: July 2007

AbstractObservation of low temperature resonant Raman scattering in AgBr involving the TA(L) momentum‐conserving phonon for the first time, allows symmetry‐forbidden indirect exciton transitions to be studied in silver halides. From analyzing the energy dependence of scattered intensity, in terms of impurity trapping and intra‐ and intervalley exciton scattering, relative scattering probabilities are determined for these relaxation processes. The exciton‐TA(L)‐phonon matrix element obtained with respect to that for the allowed TO(L) process is 5.5 × 10−3 (meV)−1. Taking into account the TA(L)‐assisted component, from a lineshape analysis of the indirect exciton edge a value of 28 meV is derived for the Is exciton binding energy.
Impurity States in the Presence of an Interface
Authors: Godwin V. E. , Tomak M. 
Published: July 2007

AbstractA modification of the effective mass approximation in the Sham‐Nakayama approach is discussed. Binding energies are calculated as functions of electric field, scattering length, and distance of impurities localized at the interface between SiO2, and an n‐type inversion layer on Si (001).
Photochemical Hole Burning in Polycrystalline and Neutron Irradiated NaF
Authors: Ortiz C. , Afonso C. N. , Shelby R. M. , Tropper A. C. , Bjorklund G. C. 
Published: July 2007

AbstractSpectroscopic properties of aggregate color centers in polycrystalline NaF thin films are measured for the first time by photochemical holeburning. A comparison with single crystals shows that the density of the color centers, and both the inhomogeneous linewidth and holewidth are increased in the polycrystalline material. Also studied are the effects of two different irradiation sources (neutrons and X‐rays) in single crystal samples. The excited state lifetime T1 of the 6070 Å centers is found to be very similar in all the samples.
Mössbauer and Positron Studies of Superconducting Oxides BaPb1−xBixO3
Authors: Groznov I. N. , Ionov S. P. , Kevdina I. B. , Lubimov V. S. , Makarov E. F. , Marchenko O. V. , Mikhailov N. N. , Onischuk V. A. , Shantarovich V. P. 
Published: July 2007

AbstractMössbauer spectra and lifetime positron distributions are studied for BaPb0.99−xSn0.01BixO3 samples with 0 ≦ x ≦ 0.4 containing Sn119 as Mössbauer label. A correlation is observed between the dependence of room temperature parameters of Mössbauer and positron spectra on x and transition temperatures to superconducting state Tc(x). The data obtained are interpreted in terms of bielectron transfer over bismuth centers.
Influence of SiSi Bonds on the Local Electronic Density of States of a‐SiO2
Authors: Grafe T. , Strehlow R. 
Published: July 2007

AbstractResults of cluster‐Bethe‐lattice calculations for complexes of Si—Si bonds in a‐SiO2 are presented. The influence of such Si04(ySi, [4 − y]O) defects on the local electronic density of states (LDOS) of SiO2 is discussed. For all values of y = 1, 2, 3, 4 localized occupied and empty defect states are found in the SiO2 gap. From cluster calculations using a bond‐orbital representation the defect functions are calculated. The local gap of these defects is distinctly changed only for y = 1, reflecting the x dependence of the SiOx gap for higher x values.
Analysis of Anharmonic Properties of Some Partially Covalent Crystals
Authors: Singh R. K. , Khare P. 
Published: July 2007

AbstractThe anharmonic properties of silver, thallium, and copper halides are analysed by means of a new interionic potential model which incorporates theeffects of the long‐range Coulomb and three‐body interactionsand the short‐range van der Waals (vdW) attraction and overlap repulsion extended up to the second‐neighbour ions. The model potential is applied to investigate the third‐order elastic constants and the pressure derivatives of second‐order elastic constants of the crystals. Additively some thermodynamic and thermoelastic behaviours of these solids are calculated. The results agree fairly well with the available experimental data and show a consistent trend throughout.
The Effect of Relaxing Defects on the Spin—Lattice Relaxation at Ferroelectric Phase Transitions
Authors: Geppert U. , Kühnel A. 
Published: July 2007

AbstractSpin—lattice relaxation times are calculated near the phase transition for a uniaxial ferroelectric containing defects. The defects are assumed to couple linearly to the order parameter. Defects and order parameter are of relaxator type. The corresponding Langevin equations are given and solved with help of perturbation theory for small anharmonicity and weak influence of the randomly located defects on the Curie temperature. It is found that the experimentally observed opposite anomalies of the spin—lattice relaxation times in TGS can be understood for definite values of the defect parameter.
Application of the Quadratic Response Theory to the Screening of a Positron in an Electron Gas of Metallic Density
Authors: Rubaszek A. , Stachowiak H. 
Published: July 2007

AbstractThe screened Coulomb potential following from the quadratic response theory is modified and applied to the Kahana equation for a positron in an electron gas. Electron—electron correlations are taken into account in a local way, proposed by Shaw. For the first time within this formalism no divergence of the total annihilation rates occurs in the low density region. Self‐consistency, according to the total screening charge around the positron, is approached. The momentum dependent enhancement factors are found to be in good agreement with the experimental data.
Calculation of the Jahn‐Teller Coupling Forces for ZnS:Cu2+ and GaP:Ni+
Authors: Welnert C. M. , Scherz U. 
Published: July 2007

AbstractThe Jahn‐Teller coupling forces for the deep d level impurities ZnS:Cu2− and GaP:Ni+ are calculated with a cluster model. The calculation consists of a self‐consistent LCAO calculation of a cluster of 17 atoms with the impurity in the center. The Jahn‐Teller active modes of ω and τ2 symmetry are modelled by the corresponding small distortions of the ligands nearest to the impurity. Coupling forces to the ω and τ2 modes are found to be of similar strength. There is only weak coupling to optical and localized modes in contrary to what has been assumed so far. A strong Jahn‐Teller effect which could account for the strong quenching of the ground state g factor observed in these centers is only possible by coupling to the acoustic modes.
A Dynamic Percolation Approach to the Andrade Creep
Authors: Schönhals A. , Donth E. 
Published: July 2007

AbstractA new approach to the Andrade law of creep relaxation is given. Starting points are the theory of linear response and the fluctuation‐dissipation theorem (FDT). According to the FDT the macroscopic shear complianceis determined by the correlation function of shear angle fluctuation of a functional subsystem. An investigation of the shear pulse response leads to the conclusion that the subsystem must be considered as a temporarily inhomogeneous solid. A dynamical percolation model is developed resulting in a power law for the short‐time behavior of creep compliance. The relevant exponent lies between 0.3 and 0.47, definitely lower than 1/2. The experimental value for the Andrade exponent is about 1/3.
Anharmonicity Effects in IR‐Reflection Spectra of Sheelites
Authors: Efendiev Sh. M. , Nagiev V. M. , Burlakov V. M. 
Published: July 2007

AbstractReflection spectra of PbWO4 crystals vs. the temperature are studied over the 700 to 1000 cm−1 frequency region. On the basis of an invertibility criterion of the oscillator obtained in the present paper, the anomaly in the reststrahlen band in the reflection spectrum is found to be connected with a strong frequency dependence of the damping Γ(Ω) of the transverse optical vibration. A possible decay channel for an intramolecular excitation corresponding to the peak of the function Γ(Ω) is proposed.
On Correlation between Structural Features of Liquid Metals and the Effective Ion–Ion Potential
Authors: Gelchinskii B. R. , Ryskulbekova R. M. 
Published: July 2007

AbstractA comparison of ion–ion interaction potentials obtained by various methods is performed. A certain similarity of potentials using empirical information and their distinction from priori potentials are noted. A correlation is found of the short‐range part of the effective ion–ion potential obtained by the Percus‐Yevick equation with radial distribution function form. It is suggested to use this correlation both, for developing methods of a theoretical estimation of ion–ion potentials and for revealing some specific features in the structure of melts.