bluuebunny/crossref_metadata_2025_split huggingface dataset:
Raman scattering in mixed crystals
Authors: Martin T. P. 
Published: July 2007

AbstractA simple model is used to describe the relative intensity of Raman scattering in mixed crystals with two mode behaviour. The local susceptibility, both linear and nonlinear, is assumed to be a sum of concentration independent atomic contributions. The four independent nonlinear model parameters are determined by the electro‐optic and second harmonic generation coefficients of the pure component materials. The concentration dependence of the Raman intensity of a longitudinal mode can demonstrate an antiresonance. Explicit calculations are made for CdS1‐xSex.
Elastic, optical, and dielectric properties and their pressure derivatives of rutile‐structure oxides in a modified rigid ion approximation
Authors: Striefler M. E. , Barsch G. R. 
Published: July 2007

AbstractThe elastic and static dielectric constants and their first pressure derivatives, and the optical mode frequencies and mode gammas at zero wave vector have been calculated for GeO2, TiO2, and SnO2 from a modified rigid ion model, in which first and second nearest neighbor central force repulsive interaction of Born‐Mayer type and oxygen–cation–oxygen angle bending forces are included. The nine free parameters of the model are determined from a least squares fit to the zero pressure values of the optical frequencies and elastic constants. The agreement with the experimental optical and elastic data at zero pressure is very good, and fair to moderate for the pressure derivatives.
Luminescence spectra of nitrogen in solid argon I. Experiment
Authors: Jodl H.‐J. , Bruno R. 
Published: July 2007

AbstractThe X‐ray stimulated luminescence spectra of Ar crystals having 0.01% and 5% N2 impurities were studied at 4.2 and 77 K, in the region of the Vegard‐Kaplan (A3Σ → X1ΣΣ) bands. Each band of the 5% N2/Ar system, at 4.2 K, was composed of three, almost equispaced, peaks. The fine structure was defined by a two‐peak asymmetric sideband, between 25 and 180 cm−1, to the red of the N2 electronic‐vibrational transition. At other impurity concentrations and crystal temperatures, different relaxation rates were found but no fine structure was observed. The whole Vegard‐Kaplan band system for N2/Ar at 4.2 K was found to be shifted by (128 ± 15) cm−1, to the red of V00,. the free molecule transition.
Observation of CESR in high‐purity aluminium by a reflection spectrometer
Authors: Janssens L. , Stesmans A. , Cousins J. , Witters J. 
Published: July 2007

AbstractThe observation of CESR in a 6N aluminium sample using a reflection spectrometer operating at 21 GHz is reported. The main characteristics of the signal are a g‐factor close to 2 and a linewidth varying from 52 G at liquid He temperature to 190 G at 150 K. A minimum of 38 G is found near 20 K. The results are compared with the many body effect theory of Fredkin and Freedman. Good quantitative agreement is not found with the results of Lubzens et al. The results also indicate a g‐value variation in the phonon dominated regime.
Hydrogen vibrations in strontium chloride
Authors: Hayes W. , Wiltshire M. C. K. , Jtjmeatj D. , Taurel L. 
Published: July 2007

AbstractThe sideband structure of the local mode of H− in SrCl2 has been measured. A simple lattice dynamical model including a change of mass at the impurity site and a change of nearest‐neighbour central force constant has been used to calculate this structure. Lattice Green functions computed from the shell‐model parameters of Kuhner et al. were used in the calculation. With this model, agreement with the H− and D− local mode frequency was obtained for central force constant reductions of 53% and 56%, respectively. The sideband structure contains a resonance at 50 cm−1. A reduction of 32% in the central force constant was required to obtain agreement between the calculated and observed frequencies.
The role of a double oxygenous bridge in radiation‐induced centre formations in glasses from EPR data
Authors: Cherenda N. G. , Yudin D. M. 
Published: July 2007

AbstractExperimental data for effects of various penetrating radiations on oxidic glasses and of changes in the isotopic composition of the glasses on induced electron paramagnetic resonance (EPR) spectra are presented. It is found that the present interpretation of investigation data of radiation centres in irradiated glasses is inadequate. A mechanism of paramagnetic centre formation which is different from an electron–hole mechanism and which allows to interpret the experimental data correctly is proposed.
A general formulation of the dynamical theory of electron diffraction including absorption
Authors: Andrew J. W. , Sheinin S. S. 
Published: July 2007

AbstractGeneralized perturbation theory has been used to derive an exact solution to the matrix form of the equations of the dynamical theory of electron diffraction including absorption. It has been shown that the introduction of the imaginary potential leads to a mixing of the unperturbed Bloch waves characteristic of the system without absorption. Numerical calculations have been presented which show that it is important to take the mixing of Bloch waves into account in high atomic number materials and when quasi degeneracy of the kinetic energies of the unperturbed Bloch waves is obtained.
The role of the spin‐spin interaction reservoir in nuclear relaxation
Authors: Skrebnev V. A. 
Published: July 2007

AbstractThe role of the dipole–dipole interaction reservoir (DDR) of impurity ions in the nuclear relaxation is considered based on the idea of the interaction temperature between the nuclear and the dipole–dipole systems. The condition in which the DDR can be heated and the effect of this heating on nuclear relaxation are investigated. The expression has been obtained which takes into account the role of transverse components of the magnetic moment of impurity ions in nuclear relaxation.
Effect of impurities on magnetic properties of ferromagnetic and almost ferromagnetic metals
Authors: Strauss M. , Ron A. 
Published: July 2007

AbstractAn investigation is made of the effect of the mean free path due to static impurities on the dynamic susceptibility of ferromagnetic and almost ferromagnetic metals. Using the itinerant electron model, in the random phase approximation the equation of motion of the density matrix – the quantum kinetic equation – is derived in the presence of an external spatial and time‐dependent magnetic field. The impurities are introduced by generalization of the relaxation time approximation and application of the conservation laws to the collision term of the kinetic equation. The linear response of the system to the small external field is calculated by linearizing the kinetic equation, and the dynamic susceptibility is obtained. The dynamic susceptibility, which depends now on the mean free path, enables the investigation of the magnetic properties of the system.
Calculation of EPR spectra of Fe3+ with high zero‐field splitting in polycrystalline materials
Authors: Shcherbakova M. Ya. , Istomin V. E. 
Published: July 2007

AbstractExpressions of the shape of EPR spectrvim in a polycrystal for a paramagnetic centre with an effective spin S = 1/2 and an anisotropic g‐factor are obtained. Based on these expressions the model spectra of Fe3+ (6S5/2) with a large zero field splitting are calculated as derivative curves of the absorption and the results are analysed.
Binding energies and wave functions of Wannier excitons in uniaxial crystals—A modified perturbation approach II. Applications
Authors: Gerlach B. , Pollmann J. 
Published: July 2007

AbstractA modified perturbation approach is used to describe anisotropic Wannier excitons. The influence of small external fields on the energy levels is discussed. The whole scheme is examplified in the case of GaSe and CdSe; anisotropy parameter and masses can be calculated in a consistent way.
Properties of a 5T2 in iron (II) under the action of arbitrary‐symmetry ligand fields and spin‐orbit coupling I. On the quadrupole splitting
Authors: Zimmermann R. , Spiering H. 
Published: July 2007

AbstractThe quadrupole splitting of the ground state 5T2 of high‐spin iron(II), split by a ligand field and spin–orbit coupling, has been treated. It is shown to depend up to a constant factor only on the energy splittings Δ1 and Δ2 of the orbital states, the spin–orbit coupling constant λ, and the temperature, but not on the orbital eigenstates of the ligand field. The well‐known method of fitting ligand field parameters from the temperature dependence of the quadrupole splitting now can be applied even in the case of low symmetry ligand fields without having trouble with too many parameters. From the temperature dependence of the quadrupole splitting it can be only differentiated between cubic (Oh, Td, …), axial (D3, D4, D2d, …) or lower symmetry (D2, C2v, C2, …, C1) ligand fields. A formula for calculating the components of the EFG in low symmetry ligand fields is derived.
The effects of a variable field of differential frequency on spin‐system dynamics
Authors: Skrebnev V. A. 
Published: July 2007

AbstractEffects are investigated arising from the superposition of a field with a frequency equal to the difference of the resonance frequencies of two kinds of magnetic centres in a sample. The external variable field is regarded as a sub‐system with infinite temperature. The cross‐relaxation between the two kinds of magnetic centres is considered as to be sufficiently pronounced. The conditions have been found under which it is possible to observe resonance effects, and their role in the spin‐system dynamics is considered.
Luminescence spectra of nitrogen in solid argon. II. Theory
Authors: Bruno R. , Jodl H. J. 
Published: July 2007

AbstractA theoretical investigation of the X‐ray stimulated spectra of N2/Ar has been made. The fine structure of the N2/Ar sideband is identified as the combined result of host‐lattice vibrations, an impurity induced local mode, and multiphonon processes. The width of the peaks is attributed to hindered rotations of the trapped molecule. The details of the matrix red shift are explained via Buckingham's formulation and the effects of hindered rotations.
A theory of DC‐hopping conductivity accounting for local electrical fields and electron‐phonon interaction of arbitrary strengths
Authors: Böttger H. , Bryksin V. V. 
Published: July 2007

AbstractStarting from first principles the dc‐hopping conductivity in a disordered one‐band tight‐binding model is investigated. Equations are derived for the current which represent a generalization of Kirchhoff's equations for a steady state random network problem. These equations hold for local electrical fields of arbitrary strength and for arbitrary strong electron–phonon interaction.
The g‐factor of the conduction electrons in Bi2Se3
Authors: Köhler H. , Wöchner E. 
Published: July 2007

AbstractThe oscillatory part of the magneto‐resistance (Shubnikov‐de Haas effect) was investigated on n‐Bi2Se3 single crystals with carrier concentrations between 5 × 1017 and 1 × 1018cm−3 in the temperature range from 1.6 to 4.2 K in pulsed magnetic fields up to 35 T (350 kG) magnetic induction. Most experiments were performed for the magnetic induction B parallel to the trigonal axis c of the crystals, where the smallest cyclotron mass mc and a parabolic ε(κ) relation is present. No spin‐splitting of the Shubnikov‐de Haas resistivity extrema is observed at high quantum numbers. At low quantum numbers the influence of spin‐splitting causes a shift of the resistivity extrema and an additional maximum, which should not be present for M = gmc/(2m0) ≪ 1. A calculation of the magnetoresistance in quantizing magnetic fields based on Kubo's theory for a field‐independent carrier concentration enables the determination of the expression M = gmc/(2m0) = 2 with ±5% uncertainty for B‖ c. The absolute value of the g‐factor is evaluated hence as (32 ± 3) for B‖ c. For arbitrary crystal orientation in the magnetic field M may be assumed to be constant within the error margin, the g‐factor being consequently smaller for B ⟂ c: g ⟂ = (23 ± 3).
Thermopower calculation for variable range hopping — application to α‐Si
Authors: Overhof H. 
Published: July 2007

AbstractAn expression for the thermopower S in the variable range hopping regime near the Fermi energy is derived. This allows the calculation of S for an arbitrary density of states, provided the localisation length, α−1, is kept constant. An application is made to estimate the density of states function of amorphous Si from conductivity and thermopower data.
Method of calculation of a typo of coherent electronic fluctuations connected with the viscosity of the electronic gas of a solid
Authors: Haymann P. 
Published: July 2007

AbstractIn the frame of optical potential the interaction of a fast electron beam with crystalline targets is considered in second order approximation. It is supposed that only the electrons produced during electron–hole interactions can be scattered. These electrons possess a behaviour of a quasi‐particle with a definite momentum. Then a calculation of the imaginary part of the crystalline pseudopotentiel coming from the electronic transitions is given.
Optical absorption edge of CdAs2‐based glasses
Authors: Voelïček V. 
Published: July 2007

AbstractThe results of the absorption edge study of some glasses based on CdAs2 are discussed in terms of internal potential fluctuations. Both the electrostatic and deformation fluctuations are present in a‐CdGeAs2 whereas in remaining glasses only the former were observed. A qualitative description of the electronic properties of these glasses offers Boer's real‐glass model. Its applicability limits are discussed. At elevated temperatures, the edges formally obey the Urbach rule. Possible reasons for this behaviour are considered.
Additional long‐ and short‐range potentials for direct excitons in zincblende structure solids: I. General correction formula
Authors: Ekardt W. 
Published: July 2007

AbstractStarting from the general equation derived for the evaluation of corrections a calculation is made within the ladder approximation and with restriction t o the particle‐hole part of the exciton amplitude, of all correction potentials which arise as a result of the expansion of the effective Bethe‐Salpeter equation (BSE) in terms of three independent translation vectors e.g. K – K′, K′ and q up to the order |wavevector|°. This means a,n expansion up to EB/Egap or EB/hωLO taking into account spatial dispersion, local field corrections, dynamical corrections, exchange interaction etc. The results are evaluated for eleven III–V or II–VI zincblende semiconductors using calculated dielectric constant values and interband oscillator strengths. Comparison with experiment is quite satisfactory.
Nuclear spin dynamics in the presence of electronic relaxation
Authors: Bosse J. , Gabriel H. , Vollmann W. 
Published: July 2007

AbstractRedfield's relaxation theory, which essentially includes all treatments published so far. has been expressed in a form which is independent of the explicit representation. The relaxation operator is given as an expression sufficiently general to deal with various types of experiments sensitive to the dynamical behaviour of a small subsystem coupled to its environment. e.g. NMR, PAD, ME. Special attention has been paid to the treatment, of a spin system of cylindrical symmetry which relaxes via magnetic dipole interaction with the surroundings. The fast and slow relaxation regime as well as the transition between them is considered. As an application the Mössbauer relaxation spectra of FeNH4(SO4)2·12H2O are discussed.
Lattice dynamics of covalent ionic compounds (I)
Authors: Altshuler A. M. , Vekilov Yu. Kh. , Izotov A. D. 
Published: July 2007

AbstractThe dynamics of covalent ionic crystals in terms of the “dielectric model” is analysed. Non‐diagonal elements of the screening matrix correspond to both the bonding charge and the anion localized charge. The dynamic matrix reflects the screened Coulomb interaction between the ions and the point bonding charges, the short‐range part being described by two parameters. The phonon dispersion in high symmetry directions of the Brillouin zone and the elastic constants are calculated for Si, GaAs, ZnS, and CuCl. It is shown that the interaction between the localized charges should not be taken into consideration in calculations of the crystal energy.
The role of annealing on the optical absorption edge of CdAs2‐based glasses
Authors: Vorlíček V. 
Published: July 2007

AbstractThe influence of annealing on the absorption edge of some glasses based on CdAs2 was studied. Samples annealed at t<tg (tg, being the softening temperature) behave similarly as non‐annealed samples. Their properties are discussed in terms of the CS concept. Samples annealed at t ≈︁ tg recrystallize. The influence of disordering on the band structure of compounds CdAs2, and CdGeAs2 is discussed.
A high pressure search for K′‐bands in KBr and KI
Authors: Mamola K. C. 
Published: July 2007

AbstractThe optical F‐band in KBr has been studied at pressures up to 11 kbar and in KI up to 9 kbar. No new absorption bands were found to appear nor was any other anomalous behavior observed. It is thus shown that so‐called K′‐bands observed by previous investigators and the K′‐center to which they were attributed do not in fact exist in crystals subjected to hydrostatic pressure.
On the theory of the Wannier‐Mott excitons in disordered semiconductors
Authors: Bonch‐Bruevich V. L. , Iskra V. D. 
Published: July 2007

AbstractTwo problems of the Wannier‐Mott exciton theory in disordered semiconductors are considered: a) limitation of the exciton life‐time due to the second kind collisions with the random field and b) influence of the excitonic effects upon the interband light absorption and emission. The first factor is shown to be of interest in some photoconductivity experiments while being relatively unimportant in interband optics. The role of the second factor depends upon the relation between the exciton binding energy and the characteristic energy of a charge carrier in a random field: the slope of an exponential optical tail depends upon which of the two energies is dominating.
Effect of the trigonal field and a uniaxial stress on the vibronic triplet states of (3d)n ions in α‐Al2O3
Authors: Lacroix R. , Duval E. , Champagnon B. , Louat R. 
Published: July 2007

AbstractThe local strain around the cation is expressed in function of the ion displacements in the cluster. It is shown that this local strain is related to the applied uniaxial stress by “local elastic compliances” which can be different from the crystal elastic compliances. The strain Hamiltonian which represents the ion‐strain interaction is given for any direction of pressure. Experimental parameters are defined, allowing to interpret the effect of the uniaxial stress on the transition between the fundamental vibronic singlet and the three lower vibronic states originating from T1 or T2 states in cubic symmetry.
Double reflection dips from grating ruled semiconductors
Authors: Teng L. F. , Alexander R. W. , Bell R. J. , Fischer B. 
Published: July 2007

AbstractThe double reflectivity dips, previously observed by Fischer et al. and Anderson et al., which appeared in the reflection spectra of grating surfaces on, the Te‐doped semiconductors GaAs and InSb around both the plasmon and phonon frequencies have been measured in more detail. In the plasmon region, several possible explanations of the phenomenon are discussed, but the favored explanation involves surface damage. A simple two‐region reflectivity equation checked with a rigorous grating theory is proposed and is shown to fit the data well.
The optical properties of LiNbO3
Authors: Bärner K. , Braunstein R. , Weakliem H. A. 
Published: July 2007

AbstractThe optical constants of LiNbO3 from 0.3 to 14.5 eV are presented from a Kramers‐ Kronig analysis of the near normal incidence reflectivity spectrum. Comparison with the cubic perovskites suggests that the electronic transitions from 3.5 to 12 eV are between the O2‐2p valence band and Nb4+ d‐like conduction band states. Higher transitions are most likely into Li+ 2s states. Sum rules are applied to calculate the effective number of electrons involved; this number is found to be consistent with the above assignment. Also, the combined density of states function is found to be very similar to that calculated for the analog compound KTaO3.
Temperature dependence of Pb3+ EPR spectrum in irradiated calcite
Authors: Popescu F. F. , Grecu V. V. 
Published: July 2007

AbstractThe spin‐Hamiltonian parameters and the line widths of Pb3+ in CaCO3 have been measured over the temperature range 77 to 300 °K. The hyperfine interaction is very large so that the intermediate field approximation was used. The hyperfine interaction decreases as the temperature increases, in agreement with the effect of lattice‐vibrations on the ground state. The hypothesis of a large‐amplitude resonance mode is used for explaining the qualitative temperature dependence. Extra line widths is described to the presence of hyperfine interaction of the 207Pb isotope. A dynamic process is assumed which is related to the change of spin−lattice relaxation via phonon modulation of the hyperfine interaction.
A contribution to the discussion on the relaxed excited F centre
Authors: Bosi L. , Cova S. , Spinolo G. 
Published: July 2007

AbstractAn interpretation is given of the behaviour of the relaxed excited F centre in terms of a hydrogenic model with broad wave functions. In particular the dependence is considered of the lifetime τ on the host crystalline matrix at a fixed low temperature, and on the temperature T for a given matrix. Precision experimental data are given for τ(T) in NaCl, RbCl, and KBr.
Magnetic properties of superconductors with uniaxial symmetry
Authors: Takanaka K. 
Published: July 2007

AbstractIn type‐II superconductors with uniaxial symmetry the three critical fields (Hc1, Hc2, Hc3) are calculated near the transition temperature Tc using the anisotropic Ginzburg‐Landau equations. It is shown that in general an induced magnetic field δH⊥ perpendicular to the applied magnetic field exists and that the anisotropy removes the degeneracy in the direction of the flux‐line lattice. The pattern and the orientataion of the flux‐line lattice are in good agreement with the experimental results of technetium.
Electroabsorption and electroreflectance of PbI2
Authors: Daunois A. , Deiss J. L. , Nikitine S. 
Published: July 2007

AbstractElectroabsorption and electroreflectance spectra of thin and thick single crystals of PbI2 have been investigated at 85 and 4.2 °K. In the vicinity of the fundamental edge, the main excitonic series is well resolved in both spectra. An important temperature dependence is observed for this series. Different electroabsorption or electroreflectance structures are also studied beyond the fundamental edge.
Lattice dynamics of rare‐gas solids by Kihara's potential: II. Specific heat and thermal expansion
Authors: Agrawal T. N. , Gupta R. K. , Gupta G. L. 
Published: July 2007

AbstractThe specific heat and thermal expansion of rare‐gas solids have been computed by studying the lattice vibrations of these solids using Kihara hard core potential. The theoretical calculations have been compared with the other theoretical results and available experimental data.