bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusional Relaxation of Crystal Lattice Defects in the Fields of Local Lattice Disturbances
Authors: Estrin Yu. Z. , Khachaturyan A. G. 
Published: July 2007

AbstractDiffusional relaxation of mobile defects in crystals containing local disturbances is considered. It is shown that the distribution density of the inverse relaxation times in such a system calculated as the imaginary part of the trace of the diffusion equation Green's function may involve resonance maxima. Their positions are determined by the interaction potential of the mobile defect and the immobile local perturbation center. The relevant internal friction peaks when detected provide a possibility of investigating this potential. The distribution density of the inverse relaxation times is calculated for a number of particular systems which model the diffusional relaxation of point defects in the local fields of a point disturbance and of a plane defect and the kink relaxation in the presence of a disturbance. It is shown that several internal friction peaks can be associated with a single relaxation mechanism.
Stress‐Dependence of the Raman Frequencies and Elastic Constants of Cubic Semiconductors
Authors: Bell M. I. 
Published: July 2007

AbstractA model proposed by Keating to describe the second‐ and third‐order elastic constants of diamond‐structure crystals is used to calculate the parameters (p, q, r) which characterise the stress‐induced shifts and splittings of k = 0 optical phonon frequency. The results for Si and Ge are in good agreement with experiment. If the electrostatic contributions to the elastic constants and Raman frequencies are neglected, the model may be applied to zinc‐blende‐type crystals, but the results obtained in this way for GaAs and InSb are less satisfactory.
Lattice—Ion Interactions in the Ligand Field Theory of Trigonally Distorted Octahedral V3+ Complexes
Authors: Bhattacharyya B. D. 
Published: July 2007

AbstractThe theoretical expressions for the magnetic susceptibility and g‐values of trigonally distorted octahedral V3+ ion have been developed on the basis of molecular orbital method of Stevens [19] and Bose et al. [20]. Results are discussed considering the less strong vibronic coupling (dynamic Jahn‐Teller effect) in which an orbital triplet interacts with the vibrational E‐modes of the ligands. Comparison is made with experimental results on magnetic susceptibility, g‐values, and optical absorption with a unique set of values of parameters in the theoretical expressions at all temperatures. The Jahn‐Teller coupling parameter appears to be appreciable in some of the complexes.
Study of Molecular Motions in Liquid Crystalline MBBA by Cold Neutron Scattering
Authors: Dimic V. , Barbič L. , Bling R. 
Published: July 2007

AbstractSelf‐diffusion in the nematic and isotropic liquid phase of 4‐n‐methoxybenzylidene‐4′‐n‐butylaniline (MBBA) has been studied by incoherent quasielastic neutron scattering. A comparison of NMR and neutron data shows a large difference in the values of the diffusion coefficients, D, indicating that rotational as well as translational diffusion contribute to the self‐diffusion coefficient observed by the neutrons. These measurements are contrasted with those of PAA where translational diffusion is dominant.
The Influence of the Non‐Locality of Shaw's Model Potential on the Band Structure of Be
Authors: Taut M. 
Published: July 2007

AbstractThe influence of the non‐locality of Shaw's model potential on the band structure of Be is investigated. A method is given for the treatment of the energy dependence of a linear energy dependent potential. The energy dependence of Shaw's model potential causes an increase of the band width. The density of states and the Fermi surface using the non‐local model potential agree well with experiment whereas the local approximation is not appropriate.
Non‐Local Screened Exchange in Copper
Authors: Stöhr H. , Bross H. 
Published: July 2007

AbstractThis paper reports an investigation of solid copper using a nonlocal screened exchange. It is shown that the energy bands strongly depend on the screening constant. Its optimum value obtained by a fit to several experiments yields an excellent agreement with measured energy differences of the valence bands as well as reasonable results for the higher core levels.
Coincidence Site Lattices
Authors: Fortes M. A. 
Published: July 2007

AbstractThe general conditions for the occurrence of a coincidence site lattice, i.e., for partial coincidence of lattice points in two identical crystal lattices, are derived and a method is outlined for determining the degree of coincidence. The question of atomic coincidence in two actual crystals is discussed, leading to the concept of mixed coincidence (coincidence of non‐equivalent atomic sites).
Atomare Fehlstellen mit niedriger Symmetrie in inhomogenen Spannungsfeldern
Authors: Hornung W. 
Published: July 2007

AbstractZur Beschreibung der Bewegung atomarer Fehlstellen mit niedrigerer als Gittersymmetrie wird eine allgemeine Methode unter Verwendung von Ratengleichungen angegeben und an speziellen Beispielen durchgeführt. Dabei werden Umorientierungs‐ und Wanderungsprozesse gleichzeitig berücksichtigt. Der Fall inhomogener Spannungsfelder wird durchgeeignete Transformationen auf den Fall homogener Felder zurückgeführt. Das zugehörige hochdimensionale Gleichungssystem wird nach räumlicher Fourier‐Transformation durcheinen Relaxationsansatz gelöst. Bei inhomogenen Feldern tritt eine bisher unbekannte Relaxationsfunktion auf, deren Zeitkonstante mit den von diesen Feldern induzierten Wanderungsschritten verknüpft ist. Die zugehörige Aktivierungsenergie unterscheidet sich von der im Snoek‐Effekt gemessenen, falls die Aktivierungsenergie der lokalen Umorientierung kleiner ist als die der Wanderung.
Dielectric Function of a Model Semiconductor
Authors: Rashenov V. K. , Foigel M. G. , Alarashi R. A. 
Published: July 2007

AbstractPenn's model of an isotropic semiconductor is used to calculate ε1(q), the real part of the static dielectric function. With the aid of the optical f‐sum rule the expression for the interband transition matrix element is obtained which is different from that of Penn. The calculations reveal close correspondence of ε1(q) with that of other authors obtained from the realistic model of the band structure. The dielectic functions of Si, Ge, Gap, GaAs, and ZnSe crystals are given.
Relaxation and Nuclear Dynamic Polarization in the Case of Inhomogeneous EPR Broadening
Authors: Buishvili L. L. , Zviadadze M. D. , Fokina N. 
Published: July 2007

AbstractThe time of nuclear relaxation and the amplification coefficient of polarization in diluted paramagnetic crystals with inhomogeneous broadening of EPR and with allowance for nuclear spin diffusion are calculated in various limiting cases.
The Influence of Interatomic Correlation on the Instability of the Paramagnetic State in an Orbitally Nondegenerate Narrow Band
Authors: Schneider J. , Heiner E. , Haubenreisser W. 
Published: July 2007

AbstractThe role of the interatomic correlation on the paramagnetic instability against the ferromagnetic state in an orbitally nondegenerate narrow band is discussed in the frame of an extended Hubbard Hamiltonian. It is concluded that the intra‐atomic Hund's‐rule coupling in orbitally degenerate bands seems to be more important to stabilize a ferromagnetic state than the interatomic correlations in an orbitally nondegenerate band.
Temperature Dependence of the Knight Shift in Na in the Nearly‐Free Electron Approximation
Authors: Islam M. M. , Sarker A. Q. 
Published: July 2007

AbstractIn the nearly‐free electron approximation the temperature dependences of the Knight shift in liquid and solid sodium are determined using the experimentally measured structure factors and the temperature‐dependent pseudo potential of Islam and Ball. The calculated values are in excellent agreement with experiment.
Perturbation Study of the Uniaxial Stress Effect on the EPR Spectra of Γ8 Ions
Authors: Passeggi M. C. G. 
Published: July 2007

AbstractPerturbation theory has been used to derive the shift of the energy levels of a Γ8 system under the effect of a uniaxial stress applied along the [110] axis. The results are correct up to second order in the perturbation parameter f/g (f/g is the ratio between cubic and linear terms in spin variables of the unstressed spin‐Hamiltonian), and up to second order in the stress. The formalism could also be extended to include higher order terms. The results are valid for all values of the angular variable provided that − 1/6 < f/g < 1/9. Otherwise for certain angles, some expressions become invalid.
Surface Phonons in Spectral Oscillations in the Photoconductivity on Silicon (111) Surfaces
Authors: Ibach H. , Mönch W. 
Published: July 2007

AbstractAt clean cleaved silicon (111) surfaces an “oscillatory” photo conductance with excitation of holes out of surface states has been reported [1]. The period of the oscillations is (58 ± 3) meV. A surface phonon (hωs = (56 ± 1) meV) has been found on the same type of surfaces in low energy electron spectroscopy [7]. It is shown that the oscillations in the photoconductivity are caused by the interaction of photoexcited hot holes with the surface phonon.
Antiferromagnetism in Amorphous Carbon Films
Authors: Macfarlane J. M. , McLintock I. S. , Orr J. C. 
Published: July 2007

AbstractMeasurements of the ESR absorption in amorphous carbon films over the temperature range 77 to 300 K provide evidence of an antiferromagnetic transition at 100 K. This transition temperature is not affected by prior annealing of the films in vacuo at temperatures up to 550 K. The ESR line width is independent of temperature between 77 and 300 K. The relationship of these results to current theories on the structure of carbon films and related materials is discussed.
Perturbation Theory for a Spin System
Authors: Trimper S. 
Published: July 2007

AbstractThe spin 1/2 Heisenberg ferromagnet is treated by perturbation theory. To avoid the difficulties connected with the unusual commutation relations of spin operators the Dyson‐Maleev transformation is applied. The corresponding Bose system is described by the Bose‐Green function. To calculate the thermodynamic behaviour of the spin system a relation has been found between spin and Bose‐Green function. The low temperature expansion of the magnetization is calculated. No agreement is found using Dyson's standard result.
Electric Field Effect on Two‐Photon Transitions near Thresholds in Solids I. Three‐Band Model
Authors: Yang E. 
Published: July 2007

AbstractThe expressions for the two‐photon absorption coefficient of solids in the presence of a uniform electric field are derived in a closed‐form. The result, can be expressed in terms of Airy functions where the effective mass approximation and a three‐band model are assumed for a solid. The finite‐field of the imaginary part of the dielectric function due to two‐photon absorption reduces to the convolution of the zero‐field dielectric function with Airy function. As in the one‐photon case, this calculation predicts different spectral dependences for the absorption coefficient at different critical points in the band structure of solids. It is also shown that the peak heights of the spectra depend on the position of the intermediate state.
Pressure Effect on the Fermi Surface of Molybdenum, Tungsten, and Rhenium
Authors: Svechkarev I. V. , Pluzhnikov V. B. 
Published: July 2007

AbstractEmploying the de Haas‐van Alphen effect, the behaviour of small cross‐sections of the Permi surface under pressure has been studied on Mo, W, and Re. The results are discussed in terms of a simple empirical model for spectrum changes under pressure. The model also involves the deformation of d‐band and its shift relative t o the s·p band. The possibility is shown of obtaining quantitative information on the behaviour under pressure of the fundamental parameters of the transition metal energy spectra on the basis of studying small cross‐sections of the Fermi surface.
A Discussion and Generalization of Bethe's Second‐Order Approximation
Authors: Serneels R. , Gevers R. 
Published: July 2007

AbstractUsing the Howie and Whelan system a perturbation technique is presented, based on the Löwdin partioning technique, to take into account the effect of weak beams in contrast calculations. This method is a generalization of the well known Bethe second order correction method. The usual Bethe method is found in the limit of very small weak beam interaction. Some explicit situations are discussed which show the limitations of the usual Bethe method for practical calculations.
Investigation of Electron Penetration and X‐Ray Production in Solid Targets
Authors: Matsukawa T. , Murata K. , Shimizu R. 
Published: July 2007

AbstractThe Monte Carlo method based on a single scattering model is applied to investigate the behaviour of electrons in pure and mixed specimens using the Electron Probe Microanalyser (Epma) and the Scanning Electron Microscope (SEM). Fairly good agreement is obtained with experiments on electron backscattering, penetration, and X‐ray production. The effect of the mean ionization potential on the final results is also discussed.
A Theory of Magnetic After‐Effect for the Irreversible Magnetization Process in Rayleigh Region
Authors: Tahara Y. , Sugeno T. 
Published: July 2007

AbstractA theory of magnetic after‐effect is reconstructed by using a new model in which the reversible and irreversible magnetizations are separately taken into account. Rayleigh's law is employed for the expression of the reversible and irreversible magnetizations. Influence of magnetic after‐effect on the reversible magnetization process is described as a usual disaccommodation phenomenon. Influence on the irreversible magnetization process is described as a change of the critical magnetic field at which a domain well starts its irreversible displacement. Initial magnetization curves are derived from these processes for the stabilized 180° and 90° walls. The results are compared with those of an experiment on the Fe‐N system. The theoretical results for 90° walls can explain the experiment very well. They also explain the non‐linear concentration dependence of the stabilization field obtained by experiment, whose origin is shown to consist in the method for obtaining the stabilization field.
Transverse Magnetoresistance of n‐Type Ge in Quantizing Magnetic Fields
Authors: Babich V. M. , Baranskii P. I. , Korolyuk S. L. , Samoilovich A. G. , Chelova T. N. 
Published: July 2007

AbstractThe anisotropy and the magnetic field dependences of ϱ⟂H/ϱ0 were investigated on n‐Ge (ne ≈ 1.59 × 1013 × m−3 cm−3) in the range of dominant phonon scattering (at 77 °K) in quantizing magnetic fields (up to 250 kOe). The developed theory is in quantitative accordance with the experimental data. It is shown that: the difference of magnetic field dependences ϱ⟂/H/ϱ0 = f(H) for H ‖ [001] or [011] (both at j ‖ [100] and at j ‖ [110]) is caused by the effect of intervalley redistribution of current carriers in quantizing H; the crystal imperfections (type of Herring statistically distributed inhomogenities) do not reveal itself noticeably at the quantization.
Electrical Resistivity and Thermoelectric Power of Liquid Alkali Metals
Authors: Rao P. V. S. 
Published: July 2007

AbstractThe self‐consistent treatment of electron correlations at, metallic densities, recently given by Vashishta and Singwi, is applied to pseudopotential calculations of electrical resistivity and thermoelectric power of alkali metals. For the liquid structure factor, recent accurate experimental data of Greenfield et al., have been used in case of Na and K, and the hard sphere structure factors in case of Rb and Cs. The pseudopotential used is a local potential of Ashcroft type, with its parameters fixed to give good agreement with phonon dispersion data. Energy dependence of the pseudopotential form factor is deduced from thermoelectric power data. Calculations have also been done with Shaw's non‐local pseudopotential for the case of Na and K. For Na, results of calculations of resistivity using three other different screening functions of Hubbard type are also presented.
Impurity Induced Raman Spectra of Annealed and Quenched NaCl: Ca Crystals
Authors: Kaiser R. , Spencler W. , Möller W. 
Published: July 2007

AbstractRaman spectra have been measured of NaCl: Ca crystals quenched or cooled slowly from high temperatures. The spectra show significant changes in structure and intensity as a function of heat treatment. The spectra of the quenched crystals are compared with the projected perturbed densities of states. Possible models are discussed in order to explain the observations.
Colour Centres in SrCI2
Authors: den Hartog H. W. , Mollema P. , Schaafsma A. 
Published: July 2007

AbstractExperimental results are reported obtained on additively and substractively coloured SrCI2 crystals. By means of combined optical and ESR experiments the position of the F‐band could be located. It was found that 02‐ impurities play an important role in the additive and substractive colouration process. The presence of O2‐ ions very strongly enhances the coagulation rate of electron excess centres formed during additive colouration. Models for radiation damage processes in O2‐ doped SrCI2 crystals are discussed.
Phenomenological Description of Aggregates of Exchange‐Bonded Paramagnetic Ions in Crystalline Environment. II. Microscopical Model for a Rectangular Aggregate of Four Paramagnetic Ions with Spin One Half
Authors: Kurzyński M. 
Published: July 2007

AbstractThe general theory of Part I is applied to an aggregate consisting of four exchange‐bonded paramagnetic ions with spin one half forming a planar rectangle. As a zero‐order approximation, eigenvalues and eigenstates of the isotropic Heisenberg Hamiltonian inside the sixteen dimensional suhspace of the low‐energetical states of the system are found. The isotropic interactions form one energetical quintet, three triplets, and two singlets; the further splitting of which are caused by anisotropic interactions and can he described in terms of spin Hamiltonian with effective spins S = 2, 1, and 0, respectively. The magnetic dipole–dipole interactions and also simple anisotropic exchange interactions are considered as & perturbation, and the microscopical model for the phenomenological parameters of the spin Hamiltonians is given in second order. Finally, the effective g‐tensors are discussed.
M Centers in Potassium Iodide
Authors: Gudat A. E. , Neubert T. J. 
Published: July 2007

AbstractAbsorption spectra of preferentially aligned M centers in Kl were measured with polarized light at 20.5, 77.4, and 243 °K. The band maxima, halfwidths, and relative intensities of the (M1, M4, M2, and M2 bands and the peak position of other anisotropies (M3, M5, M6, M7, M3, M5, M7) were determined from dichroic difference spectra. The results have been compared with M‐center data for other alkali halides and the origins of the various anisotropies have been considered.
High‐Field Antiferromagnetic Resonance in α‐Fe203
Authors: Morrison B. R. , Morrish A. H. , Troup G. J. 
Published: July 2007

AbstractMillimetre microwaves and pulsed magnetic fields have been used to investigate the magnetic resonances in a‐Fe2O3. Above the field and temperature induced phase boundary the coupling of the two weak‐ferromagnetic resonance modes has been observed. The coupling equation has been derived taking into account second anisotropy, basal plane anisotropy and magnetostriction. Below the phase boundary the antiferromagnetic resonance modes have been investigated and the resonance equations derived for the field in the basal plane. The observation of the phase boundary using a conventional resonance spectrometer has been satisfactorily interpreted in terms of the large changes in susceptibility which a numerical analysis shows often occur at or near this boundary. A small quantitative difference has been shown to exist between phenomenological theory and experiment at high magnetic fields.
Interband Magnetoreflection of ZnO
Authors: Hümmer K. 
Published: July 2007

AbstractIn magnetic fields up to 50 kOe and for photon energies greater than the band gaps for light polarized with E ⊥ c and E ‖ c oscillatory changes of reflectivity are observed on ZnO‐crystals at helium temperatures. The anisotropic reduced masses and hole masses and the energy gaps are deduced from the shift of the reflection maxima in dependence on the magnetic field (H ‖ c, H ⊥ c). The influence of the Coulomb interaction of holes and electrons and the electron‐phonon interaction on the Landau levels are discussed. The results are compared with the valence band structure of wurtzite type crystals and the band parameters of ZnO previously reported.
The M+ Center in CaF2
Authors: Collins W. C. 
Published: July 2007

AbstractS‐irradiation of additively colored CaF2 at low temperature produces two new absorption bands at 545 and 360 nm at the expense of the M band at 519 nm. These same bands can also be produced by ultraviolet bleaching at low temperature of additively colored CaF2 doped with electron trapping impurities. In addition, excitation into either band gives rise to a luminescence band peaking at 645 nm, and both absorption bands can be reversibly bleached with visible light. We propose that these bands arise from the M+ center.
Broad Neutron Groups in Inelastic Neutron Scattering and Anomalous Anisotropy of the Energy of the Dispersion Branches
Authors: Comès R. 
Published: July 2007

AbstractIt is suggested that the broad neutron groups observed in inelastic neutron scattering and in relation with structural phase transitions can be explained by the finite triple axis spectrometer resolution combined with an important energy anisotropy of the lower dispersion branches. The damped or overdamped mode concept should consequently only be used with great care in such circumstances.
Anisotropic Light Absorption in the Crystalline RbMnF3 in the Frequency Region of the 6A1g(6S) → 4E1g(4G) Transition in the Magnetic Ion Mn2+
Authors: Petrov E. G. , Kharkyanen V. N. 
Published: July 2007

AbstractA theory of one‐particle collective excitations of the cubic antiferrodielectric RbMnF3 in an external magneticfield is developed for the doubly degenerate 4E1g(4G) state of the magnetic ion Mn2+. The crystal anisotropy is taken into account. It is shown that the change in the equilibrium spin configuration in a magnetic field (which breaks the magnetic symmetry of a crystal) leads to the spin‐orbit splitting of the degenerate 4 Elg(4G) level and to the further splitting of the obtained levels into the Davydov components. The formulas for the above splittings and for the intensities of optical transitions are obtainedfor different directions of a magnetic field. The results of theoretical calculations are used to explain experimental data.
Thermodynamic Correlations in Crystalline Ferroelectric Semiconductor Solid Solutions Involving Consideration of Pressure
Authors: Yurkevich V. E. , Rolov B. N. 
Published: July 2007

AbstractThe effects of impurity concentration and hydrostatic pressure on the behaviour of the physical properties of crystals are considered in the vicinity of the phase transition point. First order as well as second order phase transitions are studied. A number of useful correlations between the physical characteristics of a crystal is obtained.
Field Effect on the Excitonic Luminescence in CsI
Authors: Grigorev V. A. , Pollini I. 
Published: July 2007

AbstractThe electric field ionization of the self‐trapped exciton is studied and the results are interpreted in terms of the Schottky effect theory. Though the possibility of internal radiationless transitions is not excluded, the idea of thermal ionization of the self‐trapped Exciton finds experimental support.