bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin‐one lattice gas model for isotherm‐reversal in spin‐labelled lipid monolayers
Authors: Chakraborty K. G. , Baret J. F.
Published: July 2007

A suitably extended version of a spin‐one lattice gas model, embodying the basic ideas of Cadenhead and Müller‐Landau and Bell and Dunne, is employed to study the “isotherm reversal” appearing in the pressure—area phase diagram of spin‐labelled monolayers. Considering the nine different configurations of molecules as concieved by Bell and Dunne the Hamiltonian is developed and the molecular field approximation is applied to derive the expression for pressure. The phase diagrams are drawn for various values of the model parameters and it is seen that the isothermreversal is a characteristic of the model itself. Unlike the one‐dimensional model of Bell and Dunne, the present model shows the phase transition from a liquid‐expanded to a liquid‐condensed phase.
Calculation of the properties and the structure of ordering alloys of the Cu—Au system
Authors: Kolodeznaya S. F. , Kozlov E. V.
Published: July 2007

By using the method of OPW‐pseudopotential (OPW‐PP) the ordering energy of copper—gold alloys, the short‐range and long‐range order structures, and the transition temperature are calculated. In many parameters the calculated values are in good agreement with the experimental ones. The level of approximation and the ways of the further development of the theory are discussed.
Towards a molecular theory of the solid—liquid phase boundary. Elementary kinetic processes
Authors: Klupsch Th.
Published: July 2007

Starting from the molecular, structural theory of the f.c.c. crystal—liquid phase boundary for onecomponent Lennard‐Jones systems near the triple point given by the author, the elementary kinetic processes of particles undergoing solid—liquid transitions are studied, and the absolute transition time is determined which is about 10−10 s. Starting with calculations of the mean square of the fluctuating force for extremely inhomogeneous systems such as the interface, and calculations of a space‐dependent friction coefficient via generalizations of the Mori formalism, the investigations are based on a description of the stochastic single‐particle motion by means of the Smoluchowski equation. It is shown that the stochastic single‐particle motion is closely related to the cell dynamics of stochastic lattice models; the corresponding absolute transition probabilities are calculated.
New arguments to the problem of screening in auger recombination in semiconductors
Authors: Ziep O. , Mocker M.
Published: July 2007

The band‐to‐band recombination rate of Auger recombination is derived by means of correlation functions of non‐equilibrium systems. In distinction to previous work where unscreened exchange interaction or static dielectric functions enter the corresponding matrix elements, the Coulomb as well as the exchange term of the Auger scattering amplitude is described by wave‐vector and frequency‐dependent dielectric functions. The results are compared qualitatively with existing calculations of Auger recombination.
A pseudopotential approach to the lattice parameters for GaAs containing impurity elements
Authors: Ito T.
Published: July 2007

A simple numerical calculation, which is applicable to estimate the impurity effects of tetrahedral compounds containing various kinds of impurity, is performed by using a pseudopotential perturbation treatment based on a simplified Heine‐Abarenkov model potential. The author proposes a new calculation method to determine potential parameters for the component elements of III–V compound semiconductors. Calculated values of total crystal energy and bulk modulus are in good agreement with the previously reported experimental data. A calculation application to GaAs lattice parameter changes caused by group VI elements (S, Se, Te) is successfully achieved.
Thermopower and thermomagnetic effects in kane semiconductors under conditions of electron and phonon heating and their mutual drag
Authors: Gasymov T. M. , Katanov A. A. , Babaev M. M.
Published: July 2007

The thermopower and the transverse Nernst‐Ettingshausen (NE) effect of degenerate semiconductors with Kane electron spectrum are considered taking account of electron and phonon heating and their mutual drag. It is established that in absence of a mutual drag and phonon heating the electron part of the thermopower Ve as well as the NE voltage U grow sharply on raising the external electric field strength ˜ E4 while the phonon part of the thermopower Vp does not depend upon E. It is shown that the phonon heating leads to a growth of the phonon parts Vp and Up with E: Vp ˜ E2 and Up ˜ E6. The nonparabolicity of the electron spectrum results in the growth of the phonon parts and the decrease of the electron parts of the thermopower and NE voltage if the phonons are nonheated. Mutual drag leads to a higher growth of all the above‐mentioned effects on raising the mutual drag degree γ0 if the electrons and phonons are heated. In the parabolic case under the conditions of a strong mutual drag (γ0 → 1) Up = 0. If the electrons are scattered by piezoacoustic phonons in a weak magnetic field the electron part of the NE coefficient Qe firstly decreases with growing γ0 (being positive), reaches zero at γ0 = 2/9, and then reverses its sign and grows in magnitude. A similar situation takes place in a strong magnetic field also, the only difference is that Qe = 0 at γ0 = 2/5.
Self‐heating of dense exciton Gas in CdTe single crystals
Authors: Baltramiejūnas R. , Kuokštis E. , Žukauskas A.
Published: July 2007

Heating of the dense exciton gas is observed in highly photoexcited CdTe single crystals radiating mainly due to the exciton‐exciton collisions at the lattice temperature T = 77 K. The effective exciton temperature turned out to be an increasing function of the excitation density while the heating is independent of the exciting quantum energy. A model of exciton selfheating due to the binding and radiative recombination processes under strong interparticle interaction is proposed for the explanation of the experimental data.
Elastic fields of dislocations piercing the interface of an anisotropic bicrystal
Authors: Belov A. Y. , Chamrov V. A. , Indenbom V. L. , Lothe J.
Published: July 2007

The elastic field of a dislocation piercing the interface of an anisotropic bicrystal is obtained for the general case of a dislocation line refracted at the interface. The theory is based on the method of dislocation‐line force fans which reduce the three‐dimensional elastic field of the dislocation in the bicrystal to the superposition of two‐dimensional fields of straight dislocations and line forces in an infinite homogeneous medium. The suggested method should be suitable for numerical calculations of the elastic fields of dislocations in arbitrary bicrystals.
Low temperature thermal conductivity of amorphous (Fe, Ni, Co) (P, B, Si) alloys and their change by heat treatment
Authors: Pompe G. , Gaafar M. , Büttner P. , Francke Th.
Published: July 2007

The thermal conductivity of amorphous metallic alloys (Fe, Ni, Co)1—x (B, P, Si)x is measured in the temperature range 2 to 100 K in the as‐produced and heat‐treated states. By taking into account the results of Matey and Anderson the influence of the nature of the metalloid and the number of metallic components can be discussed. The change of the thermal conductivity due to a structural relaxation caused by a heat treatment is very different. In the whole range of temperature a rise of the phonon thermal conductivity of the Fe—Co—B alloy is obtained, whereas no change is observed for the Fe—B alloy. At low temperature (< 40 K) the thermal conductivity of the Fe—Ni—P—B alloy increases by heat treatment, whereas at higher temperatures a reduction is observed. Additionally the thermal conductivity of the recrystallized alloy Fe80B20 is investigated.
Effect of valence band splitting on the biexciton binding energy in wurtzite‐type semiconductors
Authors: Flohrer J. , Porsch M.
Published: July 2007

A lower bound for the biexciton binding energy in wurtzite‐type semiconductors is calculated using a 64 × 64 matrix Hamiltonian obtained by the k · p method which takes into account the interband coupling‐induced nonparabolicity of the two upper valence bands A and B as well as their different anisotropies and symmetries. A properly symmetric variational ansatz for the ground state vector of the Γ1 biexciton (with AB and BB biexciton states admixed) yields an analytic expression for the binding energy. Its numerical evaluation for CdS as a function of the nonparabolicity parameters U and W shows a sensitive dependence on U, but only a weak dependence on W. It turns out that a strong valence band coupling (U = – 2h2/2m0 as proposed earlier) would result in a marked increase of biexciton binding energy due to the strong nonparabolicity of the A valence band in this case.
Changes in the electron wave phases at the exit surface of a scattering crystal located near the reflection position
Authors: Maksimov S. K. , Borgardt N. I.
Published: July 2007

The regularities in the changes of the electron wave phases at the exit of a scattering crystal are studied within the framework of the two‐wave dynamical theory for the Laue case with foil thickness and excitation error varying. The dynamical effects are shown to lead to a non‐linear phase change of the transmitted and diffracted waves. The results obtained are used to explain experimental defocused micrographs of a wedge‐shaped crystal with nanometer steps on its surface.
Texture analysis by iteration. I. General solution of the fundamental problem
Authors: Imhof J.
Published: July 2007

A summary is given of the texture analysis from the elements to the solution of its fundamental problem. The crystal symmetry of the orientation and the unreduced pole‐figure is examined. The division of the orientation space is determined from the division of the pole‐figures and vice versa. The general relation for reproduction of the orientation distribution function from pole‐figure data is obtained with the help of probability theory. The applicability of the approximative formulae is analysed.
Annealing behavior of hydrogenated amorphous silicon—nitrogen alloy films prepared by sputtering
Authors: Morimoto A. , Oozora S. , Kumeda M. , Shimizu T.
Published: July 2007

Electron spin resonance and infrared absorption measurements are performed for hydrogenated amorphous silicon—nitrogen alloy films prepared by reactive sputtering. Annealing experiments reveal the relation between paramagnetic defects and H incorporation scheme. The Si—H bond with a nearest‐neighbor N atom is found to be more heat resistant than that without a nearest‐neighbor N atom. As a result, the increment in the content of dangling bonds due to H effusion by annealing for N rich film is smaller than that for Si rich film.
A Neutron Scattering Study of Phonons in Per‐Deuterated S‐Triazine
Authors: Dove M. T. , Heilmann I. U. , Kjems J. K. , Kurittu J. , Pawley G. S.
Published: July 2007

The lattice dynamics of a fully‐deuterated single crystal of s‐triazine is investigated using the technique of coherent inelastic neutron scattering. Detailed measurements of the temperature dependence of the dispersion of the soft acoustic mode associated with the ferroelastic phase transition are reported and compared with the qualitative behaviour of other acoustic modes. The results are in agreement with an analysis of the acoustic dynamical matrix for this material which predicts that in the high‐temperature phase the combination of elastic constants C2eff = 1/2(C11 − C12) C44 − C214 should become unstable on cooling towards the transition temperature. This effective elastic constant is found to have a temperature dependence of the form Ceff = C0(T − T0) with C0 = 3.404 × 106 Nm−2K−1 and T0 = 172.4 K. Measurements of some optic mode frequencies are also reported.
Optical Quenching of Photoconductivity in a‐Si: H Films
Authors: Fuhs W. , Welsch H. M. , Booth D. C.
Published: July 2007

Thermal and optical quenching of photoconductivity are studied in undoped a‐Si: H‐films prepared by glow discharge decomposition of silane and rf‐sputtering. It is suggested that the quenching effects arise from thermal and optical excitation of trapped minority carriers (holes) and that the amount of quenching is controlled by the density of dangling bonds, which act as recombination centers. In the glow discharge deposited films one type of quenching centers is found which is attributed to states in the valence band tail. The thermal activation energy amounts to Et ≈ 0.3 eV whereas the cut‐off‐energy in the optical quenching spectra is considerably higher, E0 ≈ 0.65 eV. In sputtered films a second deeper set of hole traps exists possibly due to impurity contamination with energies Et ≈ 0.6 eV and E0 ≈ 0.9 eV.
Self‐Consistent Kink Lattice in a Quasi‐One‐Dimensional Peierls‐Fröhlich System with a Nearly One‐Third‐Filled Band. I. Analytical Solution
Authors: Fischbeck H. J.
Published: July 2007

The continuum limit of the one‐dimensional Fröhlich model with a nearly one‐third‐filled band is solved in the mean‐field approximation. The gap function connected with the static lattice distortion exhibits a periodic array of amplitude‐modulated 2π/3 phase kinks which gives rise to the formation of a band of electronic states within the Peierls gap of the trimerized phase. The selfconsistent gap function and the electronic energy spectrum are analytically calculated.
Texture Analysis by Iteration. II. Special Cases of the General Solution
Authors: Imhof J.
Published: July 2007

Three special solutions of the general system of equations in part I are examined with the help of an accurate model function. It is concluded that the parameters of the general solutions are of importance in the case of finite pole‐figure data. An unfavourable effect of the conditional ghost correction method suggested by Matthies and Vinel is shown.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration). I. Dispersion Relations
Authors: Fraitová D.
Published: July 2007

A linear solution of Maxwell's equation for the propagation of electromagnetic waves in a ferromagnetic metal in the region of ferromagnetic resonance is presented; the motion of the magnetization vector is described by the Landau‐Lifshits equation (including the exchange effect in the damping term). Dispersion relations (DR) are derived for the roots of the bicubic secular equation, representing three waves of generally combined electromagnetic‐spin‐wave character. They are compared with the DR for the case of low‐conductivity ferromagnets; the crossover effect is discussed.
Dielectric Relaxation at the Glass Transition as a Free Volume Process. A Single Relaxation Time Approach
Authors: Alegria A. , Barandiarán J. M. , Colmenero J.
Published: July 2007

Free volume theories describing structural relaxation in glasses are applied to the α‐dielectric relaxation occurring around Tg (the glass transition). Only a single relaxation time, τ, which represents the main contribution to the experimentally observed distributions, is considered. The influence of the thermal story is discussed. The unrealistic experimental values of the activation energy and preexponential factor found in the glassy zone are explained in this framework as also are the compensation laws associated with the glass transition. Measurements of τ in the range 10−8 to 104 s are performed in PVC and PAr, showing good agreement with the used model.
The Temperature Dependence of the Conductivity near the Localization Threshold
Authors: Zvyagin I. P.
Published: July 2007

It is shown that in the region of weakly localized states the conduction in both three and two‐dimensional systems may be due to non‐optimal hopping. The regime of non‐optimal hopping is characterized by a smaller hopping distance and energy compared to the conventional variable range hopping problem. The temperature dependence of the conductivity in this regime is discussed.
Order‐Disorder Phase Transition in TEA+(TCNQ)2‐
Authors: Brau A. , Farges J. P. , Filhol A. , Grassi H.
Published: July 2007

The results of measurements of cell parameters by X‐ray diffraction and of differential scanning calorimetry, versus temperature, on TEA · TCNQ2are presented and compared to the σ1de conductivity behaviour. The differential scanning calorimetry measurements show a first order phase transition at 220 K attributed to the TEA disorder. From the thermal expansion a dispersion is observed of the cell parameterafor temperatures below 220 K, attributed to a certain amount of cation “ordering” at low temperatures. The variation of the cell parameterc(the direction of the TCNQ chains), versus temperature, permits the calculation of the contribution of the TCNQ columns to the total heat capacity of the TEA · TCNQ2by a simple linear model of coupled oscillators. It is found to be dominated by intramolecular vibrational TCNQ modes and by the cation movements. The chain axis component of the Debye temperature and of the Grüneisen coefficient are θc≈ 150 K and γc≈ 7.5.
Dynamic Behaviour of the s‐d Model
Authors: Wesselinowa Julia M.
Published: July 2007

A Green function technique is developed to study the excitations and the damping of the excitations of the s‐d interaction model below Tc. The spectrum of the magnetic excitations is obtained, which consists of an acoustic and of an optical spin‐wave branch. The E+ mode is overdamped near Curie point Tc, while it is nearly undamped at low temperatures. The electronic damping is also discussed. Some numerical calculations of various effects are given, using parameters appropriate to the ferromagnetic chalcogenide spinels (such as CdCr2S4).
Phonon Conductivity of Ice Single Crystals
Authors: Kumar A. , Padhi P.
Published: July 2007

The phonon conductivity is analyzed of ice single crystals to study the role of the normal and the umklapp phonon‐phonon interaction processes.
The Interpretation of Broadened Gd3+ EPR Spectra of Polycrystalline Ceramics
Authors: Koopmans H. J. A. , Perik M. M. A. , Nieuwenhuijse B. , Gellings P. J.
Published: July 2007

An interpretation is given of the broadened EPR spectra of Gd3+ ions, which are frequently observed in polycrystalline ceramics and glasses. A reasonable simulation of the spectra is obtained, when these are regarded as a superposition of a large number of normal EPR powder spectra, each of which can be described with the usual spin‐Hamitonian. These originate from the many different surroundings of the Gd3+ ions in these compounds due to the structural disorder. The result is, that only those transitions, which are independent of the zero field splitting parameters in the spin Hamiltonian, remain visible in the derivative spectrum. The interpretation is supported by the EPR powder spectrum of the Gd3+ doped compound CaHf4O9, which changes from broadened into clearly resolved, when the compound is ordered by an annealing process.
A Model for Inhomogeneous Mixed‐Valence f‐Semiconductors
Authors: De Menezes O. L. T. , Troper A.
Published: July 2007

A simple model for an Anderson lattice, to describe inhomogeneous mixed valence f‐semiconducting compounds, is studied. The virtual excitation of 4f‐electrons to 5d‐states is an important mechanism responsible for the effective interaction between 4f‐rare earth sites. This interaction is connected to an unusual self‐energy term associated to the f‐f Green function. Considering electron‐phonon interaction in the periodic Anderson model, it is possible to describe either first order or second order semiconductor‐metal phase transitions, under increasing applied pressure. Valence changes are to be expected associated with the displayed transition.
Higher Harmonics Generated by Mobile Carriers in Semiconductors
Authors: Stramska Hanna
Published: July 2007

A theory describing the nonlinear current density in the de external magnetic fields H in semiconductors is proposed. The addition of an energy relaxation time to the Boltzmann equation provides an analytical expression for the magneto‐conductivity in a high ac electric field. It is shown that the third harmonic in the current density is not critically dependent on the dependence of the momentum relaxation time on carrier energy, thus for r = 0 (where index r describes the type of the scattering mechanism) the conductivity has the warm form σ = σ0(1 + β(ω) E.
Comment on the Identification of Z Centres in LiF:Mg and LiF:Mg, Ti Single Crystals
Authors: Watterich A. , Földvári I. , Corradi G. , Opyrchal H.
Published: July 2007

The Z‐centre hypothesis in LiF:Mg and LiF:Mg, Ti systems is re‐investigated. On the basis of available optical absorption measurements, summarizing the already emerged contradictions of this hypothesis, and by comparing the characteristic properties of the Z centres in LiF with those in other alkali halides it is established that the Z centre identifications in LiF can not be considered as proved.
Photo‐Chemical Reaction Studies in Selenium‐Doped Potassium Iodide
Authors: Prakash J.
Published: July 2007

The absorption bands due to an isolated Se2−—anion vacancy dipole in KI lie in the near ultraviolet range. Irradiation in the short wavelength absorption bands at 243 K is found to be responsible for photo‐chemical reactions (PCR). During PCR, an impurity—vacancy dipole is destroyed with the simultaneous formation of an F‐centre. No PCR is observed when the system is irradiated at LNT. Irradiation in the long wavelength absorption bands is found to be ineffective in producing PCR.
Magnetostatic Waves in a Coaxial Cylindrical Magnetic Domain
Authors: Sigal M. A.
Published: July 2007

The magnetostatic problem of a coaxial cylindrical magnetic domain (CMD) (two coaxial oppositely magnetized cylinders) is solved. A disintegrated set of equations which describe separately surface and volume modes in a CMD and the matrix is derived. The characteristic equations determining the eigenfrequencies of the magnetostatic modes are obtained. It is shown that the uniform mode in CMD is a surface one and its eigenfrequency depends on the ratio of the cylinder radii, whereas the uniform mode in the matrix is a degenerate volume mode with the corresponding frequency ωa ‐ γHa.
Band Structure Calculation of the Momentum Density in F.C.C. Manganese
Authors: Shrivastava S. B. , Ojha V. K.
Published: July 2007

A band structure calculation of the photon‐pair momentum density distributions (TPMD) and electron momentum density for Compton scattering (EMD) in f.c.c. Mn is made employing Hubbard's approximate scheme. The results of the present calculations for TPMD and EMD in Mn along [100], [110], and [111] directions are analysed in terms of their respective band structures. A comparison of the TPMD results with the EMD shows that the high‐momentum component is much higher in the case of EMD. The results of ACPAR and CP are also presented.
Optical Properties of Amorphous GeS in the Spectral Region of 18 to 38 eV
Authors: Pajasová L. , Pajas P. , Makarov O. A. , Zakharov V. M.
Published: July 2007

Synchrotron radiation is used in the measurements of the reflectance spectra of amorphous germanium monosulphide for several angles of incidence in the far ultraviolet region of 18 to 38 eV. The data are evaluated using a modification of the reflectance vs. angle of incidence method for extracting the information on n, the index of refraction, and k, the extinction coefficient. The values of the normal incidence reflectivity and the phase of reflection as obtained from n and k are matched to other experimental data of the spectral region from 0 to 18 eV. Finally, the optical properties of the material are evaluated in the whole spectral region from 0 to 38 eV. The resulting spectra of real and imaginary components of permittivity ϵ ‐ ϵ1 + iϵ2, as well as the derived quantities of −Im(1/ϵ), −Im(1/(ϵ + 1)), ϵ2ω2 and Neff, the effective number of electrons per atom engaged in optical transitions, are discussed and compared with available theoretical estimates.
Dielectric Function and Conductivity of p‐Type Semiconductors
Authors: Monecke J.
Published: July 2007

The frequency‐dependent dielectric function and the de conductivity of multiple‐band solids including interband transitions and finite life times are calculated in a relaxation‐time approximation for the example of p‐type semiconductors. It is shown that interband contributions to the dielectric function do not result in interband contributions to the dc conductivity.
Influence of Planar Defects and Disorder on the Energy Spectrum of Molecular Crystals
Authors: Primatarowa M. T.
Published: July 2007

Using the Green function approach the exciton spectrum of a molecular crystal containing planar defects is investigated. The system is presented in the nearest‐neighbour Heitler‐London approximation. The condition for the appearance of localized and quasilocalized states is obtained and the exciton energy is determined in a linear approximation in the defect concentration. Expressions are given for the density of states in some particular cases. Further, the energy spectrum of a disordered molecular crystal of a layer type is considered and the effect of the randomness of the interaction between the layers on the density of states is discussed.
Two‐Particle Solitary Waves
Authors: Mirjaniń D. Lj. , Marinkoviń M. M. , Kneževiń G. , Tošiń B. S.
Published: July 2007

A method to analyse two‐particle solitary waves is proposed. The effects of exciton—exciton interaction are omitted. The probability amplitude as well as the energies of bisolitons are found. The probability amplitude represents a modulated plane wave whose spatial part is expressed over the centre‐of‐mass coordinate. It is shown that bisolitons are bound states of two excitations.
The Discrete Variational Xα‐Method Interpretation of the C KVV and Ti L2,3M2,3V Auger Spectra of TiC
Authors: Gutsev G. L. , Shulga Yu. M. , Borodko Yu. G.
Published: July 2007

The C KVV and Ti L2,3M2,3V Auger spectra are obtained for near stoichiometric TiC. Their interpretation is based on the results of the DVM‐Xα calculations of the Auger transition energies in a cluster approach and the evaluation of each transition intensity in the one‐centre approximation. The crystal structure is accounted for in the embedding cluster model. Theoretical values of the Auger energies and probabilities of transitions allow to describe qualitatively all the peculiarities of the TiC experimental spectra.
The Electron—Hole Plasma at Finite Temperatures. Calculation of Exchange‐Correlation Energies and Padeé Approximants
Authors: Rösler M. , Zimmermann R. , Richert W.
Published: July 2007

The thermodynamics of an electron—hole plasma is investigated with special emphasis on the temperature dependence of exchange (x) and correlation (c). The basic quantity of the RPA approach used, is the free energy as a function of density and temperature. In a wide density range a remarkable compensation is found of the temperature dependence between x and c which is exemplified for the chemical potential. Numerical results are presented with parameters modelling Ge and GaAs. For the phase diagram minor changes result compared with the usual approach taking xc at zero temperature. For practical purposes Padé approximants are constructed.
Crystal Electric Field Splitting in TbNi5 and ErNi5 Studied by Inelastic Neutron Scattering
Authors: Goremychkin E. A. , Mühle E. , Ivanitskii P. G. , Krotenko V. T. , Pasechnik M. V. , Slisenko V. V. , Vasilkevich A. A. , Lippold B. , Chistyakov O. D. , Savitskii E. M.
Published: July 2007

Crystal field effects in polycrystalline samples of TbNi5 and ErNi5 are studied on the basis of inelastic neutron scattering experiments. Using the crystal field parameters derived from the neutron scattering the magnetic contribution of the specific heat capacity, the components of the static susceptibility, as well as the components of the magnetization are calculated, and compared with the corresponding experimental results for single crystals. The quadrupolar contribution of the crystal electric field B is related to the electric field gradients measured by TDPAC.
Calculation of Polarized K and L X‐Ray Emission Spectra and of Partial Densities of States of the H.C.P. Metals Be, Mg, and Zn
Authors: Rennert P. , Schelle H. , Gläser U.‐H.
Published: July 2007

Intensities for polarized X‐ray emission spectra are given by the elements of the density matrix expanded with respect to lattice harmonics. These intensities and densities of states for special values of the angular momentum and special representations of the point group are presented for Be, Mg, and Zn starting from a pseudopotential calculation. The energy dependence and the anisotropy of the radial integration is investigated. It is shown that the anisotropic spectra can be described excellently by located densities of states. Non‐diagonal elements of the density matrix give the main contribution to the anisotropy of the LII, III‐spectrum of magnesium. The spectra are broadened and compared with experimental K‐spectra. A good agreement is achieved, some discrepancy remains concerning the size of the anisotropy.
A Study of Relativistic Interface States
Authors: Roy C. L. , Roy G.
Published: July 2007

A relativistic study is made of the interface states in a solid which is reduced to a one‐dimensional system. The electronic states of such a model are governed by a two‐component Dirac equation. The interface connects two semi‐infinite solids represented by two semi‐infinite chains of δ‐function potential wells with a certain strength for either solid. In solving the Dirac equation for this model one is led to the energy—momentum relation of the system, that is to the band structure associated with non‐localised states and to isolated energy eigenvalues referring to interface states with certain complex momentum wave vectors. To eliminate isolated energy eigenvalues associated with states which increase exponentially towards the bulk on either side of the interface, existence conditions are derived which guarantee that only eigenvalues referring to interface states are selected. The influence of relativistic effects on the spectrum of interface states is demonstrated by choosing various sets of values for the parameters characterising the two solids. For the same purpose these interface state energies are recalculated for an approximately relativistic case using an approach by Steslicka and Davison, and for the strictly non‐relativistic case.
CoherentPotential Approximation for the Lattice Vibrations of Mixed III–V Crystals
Authors: Kleinert P.
Published: July 2007

The coherentpotential approximation (CPA) is applied to the lattice dynamics of some III–V mixed crystals. The calculations are based on an eleven‐parameter rigid‐ion model (RIM 11). Explicit results are reported for the one‐mode system In1−cGacP and the two mixed‐mode crystals In1−cGacSb and GaSb1−cGacAsc. Both, the reflectivity spectra and the composition dependence of vibrations at the Γ and X points are compared with existing experimental data. Force‐constant changes are considered by the virtual‐crystal approximation (VCA). The CPA theory is uniquely successful for III‐V mixed‐mode systems, which appear to switch from one‐mode to two‐mode behaviour.
Small Polaron Mobility in α‐LixO5
Authors: Sanchez C. , Henry M. , Morineau R. , Leroy M. C.
Published: July 2007

ESR and de conductivity measurements are performed on a α‐LixO5(x = 0.001) single crystal in the temperature range 4 to 293 K. They suggest that at low temperature, the unpaired electron remains localized in the field of lithium ion and is equally delocalized over four vanadium sites leading to the formation of a bound polaron characterized by a 29 hyperfine lines ESR spectrum. As the temperature is raised bound polarons are freed from the electrostatic field and the electrical properties of the sample above 250 K mainly arise from the hopping of free polarons between the vanadium sites. A comparison with previous measurements on non‐stoichiometric V2O5 shows that the activation energy corresponding to the hopping process of free polarons does not depend on the nature of the paramagnetic defect, but it appears that the energy needed to extract the bound polaron from the Coulomb field of the defect decreases when the overall radius of the defect increases.
Magnesium Colour Centres in NaF
Authors: Egranov A. V. , Nepomnyachikh A. I.
Published: July 2007

The absorption, emission, excitation spectra, and polarized luminescence of magnesium centres in sodium fluoride are studied. Three types of magnesium centres are observed. The first one, which is produced by X‐irradiation at 300 K and absorbs at 3.32 eV, is attributed to the Mgcentre. The two other centres have the electronic structure of the Mg0 atom perturbed by lattice defects. Optical excitation of the Mg0 type centres leads to two emission bands, which are attributed to the 3P1 → → 1S0 and 1P1 → 1S0 transitions. However, the structure of both of these centres are not still completly established.
Electrophysical Properties of Disordered Systems Based on Crystalline Germanium Compensated by Fast Neutron Irradiation
Authors: Konopleva B. F. , Evseev V. A. , Borisov B. A. , Nazarkin I. V. , Chekanov V. A.
Published: July 2007

The conduction of reactor fast neutron‐compensated n‐Ge (ND ≈ 1015 to 1019 cm−3) is studied. The formation of the disordered regions (DR's) is shown to generate an electrostatic potential which modulates the energy bands and affects strongly most of the electronic properties of a semiconductor. The DR‐compensated germanium is shown to possess most of the properties of the amorphous semiconductors. The Ohmic conductivity at low temperature (77 to 4.2 K) and the conductivity at moderate and strong electric fields at 77 K reveal a hopping nature.
Phonon Frequencies in GaAs
Authors: Patel C. , Parker T. J. , Jamshidi H. , Sherman W. F.
Published: July 2007

The eleven‐parameter rigid‐ion model is used to describe the lattice dynamics of GaAs. The model gives a satisfactory description of reported neutron scattering data throughout most of the Brillouin zone, and critical point phonon frequencies calculated with the model are shown to provide a satisfactory basis for the assignment of nearly all features in the reported two‐phonon infrared spectrum and second‐order Raman spectrum of GaAs.
The Coexistence of Unstable, Metastable, and Separated Frenkel Pair Defects in Solids. I. Basic Characteristics
Authors: Dzhumanov S. , Khabibullaev P. K.
Published: July 2007

The existence of unstable, metastable, and separated states of Frenkel pair defects as well as their coexistence in solids are theoretically studied. Existence region, lifetime, and equilibrium concentration of defects in these states are determined and a phase diagram of defect states for KBr is also drawn. The unstability (spontaneous annihilation) zone radius of charged and neutral pair defects are estimated. It is shown that this zone radius is very large for charged (particularly, for multiple charged) pair defects, while for neutral pairs it is about the interatomic distance. Unstable pair lifetime is estimated as ≈ 10−12 s, while metastable pair life strongly depends on crystal temperature and decreases rapidly with rising temperature. The results obtained are in good agreement with available experimental data.
Application of the Band Representations of Space Groups in the Theory of Electronic States of Crystalline Solids. II. Band Representations for Some Space Groups
Authors: Evarestov R. A. , Smirnov V. P.
Published: July 2007

The simple band representations of the space groups O, T, and D are tabulated. The results of the band structure calculations for some crystals with the symmetry of these space groups are analysed from the point of view of the band representation theory. The possible applications of band representations in the electronic state theory of local defects in solids are discussed.
Electroreflectance and Thermoreflectance Spectra of SnSe Crystals
Authors: Valiukonis G. , Gashimzade F. M. , Guseinova D. A. , Krivaitė G. , Mamedov M. M. , Šileika A.
Published: July 2007

The electroreflectance and thermoreflectance spectra of SnSe crystals are investigated in polarized light with E ∥ a and E ∥ b. The direct energy gaps are 1.05 and 1.24 eV for light polarizations E ∥ b and E ∥ a, respectively. The polarization anisotropy of modulation spectra of SnSe is strong near the gap and becomes weak at higher energies. The structures of investigated spectra in the vicinity of the forbidden energy gap are interpreted by direct optical transitions on the high symmetry line Λ‐Γ‐V in the calculated energy band structure.
Optical Anisotropy of Transition Metal Dichalcogenides. A Photoelectrochemical Determination
Authors: Kautek W. , Decker F. , Gerischer H.
Published: July 2007

Photoelectrochemical quantum efficiency measurements with polarized light incident at either (1010) or (0001) faces of VIb‐VIa compound semiconductors can be a successful probing technique for the absorption anisotropy. A condition is that the diffusion length of minority carriers towards the crystal faces being in contact with electrolyte is smaller than the reciprocal absorption coefficient, and the real parts of the refractive indices are known. It is found that the observed absorptivity ratios x/az of MoS2, MoSe2, and WSe2 attain unity near the indirect absorption edge, but gradually become considerably greater than unity for wavelengths approaching the direct transition.
Semi‐Empirical Tight Binding Calculations for the Energy Bands of the Diamond and Zincblende Type Semiconductors
Authors: Sahu S. N. , Borenstein J. T. , Singh V. A. , Corbett J. W.
Published: July 2007

A semi‐empirical molecular orbital theory is applied to study the band structures of the elemental (group IV) and III‐V compound semiconductors. The various parameterizational procedures of the elemental semiconductors are carefully studied and some of the results applied to the III‐V compounds to establish good sets of parameters for them. It is found that the orbital exponents are a set of very sensitive and important parameters in determining the correct shape of the bands in all the semiconductors.
Optical Properties of GeS
Authors: Lukeš F. , Schmidt E. , Humlíček J. , Dub P.
Published: July 2007

Reflectance and thermoreflectance are measured of single‐crystal GeS in the energy range of 1.2 to 5.2 eV in polarized light with orientations E ∥ a and E ∥ b. Kramers‐Kronig analysis is applied to all curves. Thus ε;1, ε2, Δε1, and Δε2 are obtained which are used together with the band structure of GeS calculated by Grandke and Ley and with the derived selection rules as a basis for the assignment of the characteristic energies to direct interband transitions at some symmetry points and along symmetry lines in the Brillouin zone. Some ellipsometric measurements are performed at 632.8 nm.
Calculation of the Resistivity of Liquid and Amorphous Au1−xSix Using Ziman Theory
Authors: Knuyt G. , Keupers A.
Published: July 2007

The Ziman theory is used in calculating the electrical resistivity σ and its temperature coefficient α for liquid and amorphous Au1−xSix. For the liquid the experimental σ(x) is rather well reproduced using Ashcroft pseudopotentials, while α(x) is better reproduced by the temperature variation of the mean structure factor than by the pure Ziman result. For amorphous Au1−xSix a model is proposed to calculate the various atomic structure factors from the experimental total X‐ray interference function. The resulting σ(x) and α(x) agree reasonably with experiment for x ≦ 0.3; in the other cases the Ziman theory fails, probably through the formation of localized states. It is concluded further that it can be a questionable assumption to take α equal to the variation of the structure factor at twice the Fermi wave number.
Thermoelectric Power in Inhomogeneous Metallic Polymers
Authors: Kuivalainen P. , Isotalo H. , Stubb H.
Published: July 2007

Thermoelectric power (TEP) in well conducting doped polymers is studied within a simple model in which the existence of metallic strands separated by thin potential barriers is assumed. It is shown that if the barriers dominate the dc electrical conductivity σdc(T) leading to a variable range hopping (VRH) conduction, they also give rise to a sub‐linear behaviour of TEP vs. temperature. The model predicts an enhanced TEP at high temperatures. It also indicates that due to the barriers the evaluation of Mott's parameters for VRH from the measured σdc(T) typically leads to incorrect values for, e.g., the density of states. The calculated TEP vs. temperature is compared with experimental data on heavily doped polyacetylene and polypyrrole.
Debye‐Waller Factor for Small Concentration of Mössbauer Impurities in Metallic Solids
Authors: Roy S. K. , Bhattacharya D. L.
Published: July 2007

A simple theoretical analysis is presented of Mössbauer f‐values for 57Fe impurity in a general harmonic solid using double‐time Green function technique. An estimation of Mössbauer f‐values are made taking mass disordering and force constant changes into account and treating the mass and force constant changes within separable kernel approximations. The effective host‐impurity force constant ratios used in the present work span a range 0.40 < φ′φ < 1.30. Good agreement between the results obtained from the calculations and those reported earlier is found, indicating the validity of the approximations made during the evaluation of recoilless fractions. The temperature dependences of the mean‐square displacement are also obtained for three different cases.
Tracer Diffusion and Chemical Diffusion of Hydrogen in TaHx
Authors: Potzel U. , Völkl J. , Wipf H. , Magerl A.
Published: July 2007

The chemical diffusion coefficientDcand the tracer diffusion coefficientDtof H in α‐ and α≈‐phase TaHxare measured in complementary Gorsky‐effect (Dc) and neutron spectroscopic (Dt) experiments. WhereasDcandDtdiffer only slightly forx≈ 0.28,DcexceedsDtby a factor of ≈ 20 forx≈ 0.61. The difference betweenDcandDtis chiefly determined by the value of the thermodynamic factor which is additionally obtained in the Gorsky‐effect experiments. The large difference found for the higher concentration shows that neutron spectroscopic and NMR results forDtprovide only limited information on bulk hydriding kinetics in H storage compounds.
Photochemical Conversion of MA Centres and Identification of M Centres in CaF2:Na
Authors: Rauch R.
Published: July 2007

The photochemical destruction of MA centres in CaF2:Na leads at low temperature to the formation of a new centre with absorption bands at 325 and 445 nm and a fluorescence at 635 nm. The experimental results (dichroism after polarized bleaching, time and thermal behaviour) suggest the identification of the new centre as M centre. The great shift of the absorption bands relative to the MA or M+ centres is explained by the H model fitting method developed by Aegerter and Lüty.
Complete Analytical Solution for the Zero Bandwidth s—f Model
Authors: Nolting W. , Matlak M.
Published: July 2007

The s—f model, which describes an interacting system of localized magnetic moments and itinerant conduction electrons (magnetic 4f‐, 5f‐systems), is exactly solved in the zero bandwidth limit without further restrictions. The s—f exchange leads to a splitting of the S‐“band”; into four quasiparticle sub “bands”, the spectral weights of which are strongly temperature (T)‐ and carrier concentration (n)‐dependent. For special parameter constellations certain spectral weights disappear, so that corresponding excitations are forbidden. Besides the spectral weights some relevant correlation functions as the average spin‐dependent occupation number 〈nσ〉, the density correlation 〈nσn—σ〉 The “mixed” correlation Δ↑(↓) = 〈S(±)c〉 ± 〈S1n↑(↓)〉, and especially the spin‐polarization P = (〈n↑〉 – 〈n↓〉)/(〈n↑〉 + 〈n↓〉) can be formulated as very simple functions of T, n, and spin value S. It is found a qualitatively quite different behaviour of these functions for ferromagnetic s—f coupling (4f‐systems) and antiferromagnetic s—f coupling (5f‐systems).
Study at 0 K and Various Magnetic Fields of the Triangular Magnetic Configurations
Authors: Plumier R.
Published: July 2007

At 0 K in a magnetic field the behaviour is studied of a triangular configuration built of two species of magnetic ions of spin lengths S1, S2 acted on by unequal molecular fields. The magnetic interactions considered are the interaction J between first nearest neighbours (nn) as well as the interactions J1 and J2 between first nn of the same species. In such generalized Yafet‐Kittel configurations, three types of behaviours are observed, the most disclosing features being shown while taking S1, S2, J1, J2 as parameters and h, J as variables. A comparison is made between the stability of the triangular versus the biconical configurations. Whereas second order transition lines are observed in the (h, J) diagrams corresponding to the biconical configuration, first order transition lines as well as a triple point are expected in the case of triangular arrays.
Sequence of Ferrimagnetic Phases in Er2O2SO4
Authors: Kasten A. , Hoffmann J.
Published: July 2007

Below TN = 1.5 K Er2O2SO4 is an Ising antiferromagnet. In contrast to other RE2O2SO4 (RE = = Dy, Ho, Tb, Gd) the ordering is along the crystallographic c‐axis. In external magnetic fields applied along c the antiferromagnetic phase is left via intermediate ferrimagnetic structures with multiples of 1/8 of the saturation magnetisation and enters finally the paramagnetic saturated state. The main features of the experimental phase diagram are reproduced by mean field calculations.
Soft X‐Ray Emission Spectra from Some NiAl Alloys
Authors: Maslenkov S. B. , Kozlenkov A. I. , Filin S. A. , Shulgin A. I.
Published: July 2007

A new effective method of electron microprobe grating spectroscopy is applied to the experimental investigation of the Al L2,3 (+ Ni M2,3) emission band of some nickel‐aluminium alloys. The compositional (or structural) changes in the spectra are compared with the theoretical band structure and X‐ray intensity calculations. The observed variations in the spectrum profile may be attributed to the charge transfer between the component atoms and the hybridization of s and d electronic states in the valence band.
XPS and XES Study of the Valence Band of Cr‐Al B.C.C. Solid Solutions
Authors: Ławniczak‐Jabłońska K. , Minni E. , Pełka J. , Suoninen E. , Auleytner J.
Published: July 2007

The XPS and Cr Lα ES valence band spectra of b.c.c. Cr‐Al alloys in the region 0 to 25 at% Al are presented. The shape and halfwidth of these spectra change notably at approximately 15 at% Al. The results are discussed on the basis of various simple models for the electronic structure of the alloys. The observed changes in the valence band are consistent with the results of magnetic and resistivity measurements. However, the present understanding of the changes in the electronic structure of the Cr‐Al alloys is not complete. The effect of the recently discovered inhomogeneity of the microstructure of these alloys in the upper part of the concentration region upon the electronic structure is, together with the antiferromagnetic order, the probable reason for the observed complicated behaviour of the valence band spectra with composition.
To the Theoretical Explanation of the “Universal Response”
Authors: Nigmatullin R. R.
Published: July 2007

The observation of a universal response of electromagnetic, acoustic, and mechanical influences shows the existence of some transfer processes in a medium, which are not described by a usual diffusion equation. It is shown that these processes can be explained by making use of the diffusion equation taking into account the ‘non‐Marcovian’ character of the excitation transfer process. In accordance with the experimental data a memory function is found which in one limiting case describes pure diffusion (absence of memory) and in another case turns into the wave equation (full memory). A local field frequency distribution function is suggested which confirms the suppositions made. The conditions of the realisation of the transfer process with ‘remnant’ memory are found and described by a generalized linear transfer equations in fractional derivations.