bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical Resistivity and Thermoelectric Power of Spinodal Decomposing Crystals
Authors: Schubert G. , Löser W. 
Published: July 2007

AbstractThe electrical resistivity and the thermoelectric power during spinodal decomposition in binary alloys are calculated, especially submicroscopic fluctuations are taken into account. The thermoelectric power shows a monotonous dependence on time whereas a maximum behaviour is obtained for the electrical resistivity. Both results agree with experimental observations.
The Mass Action Law in Two‐Component Fermi Systems Revisited Excitons and Electron‐Hole Pairs
Authors: Zimmermann R. , Stolz H. 
Published: July 2007

AbstractTaking up the quantum‐statistical derivation of a mass action law for two‐component Fermi systems with Coulomb interaction given previously an improved density formula for either species is presented. It expresses the densities as a sum of a free quasi‐particle part and a correlated contribution resulting from bound and scattering states. Avoiding the resolvent‐technique for the solution of the T‐matrix equation the correlated density is directly expressed in terms of on‐shell quantities, eventually the scattering phase shifts. The ionisation equilibrium of excitons, electrons, and holes is quantitatively analyzed by model calculations for a cut‐off Coulomb potential. The possibility of Bose‐Einstein condensation of scattering states is inspected.
Colour Centres and Luminescence in KCl:Zn Crystals
Authors: Bhuniya R. C. , Rao S. E. 
Published: July 2007

AbstractTL and MTL glow curves, TL spectra, X‐ray luminescence, and F bleaching characteristics of KCl:Zn crystals are studied. They are found to be very much different from those of crystals doped with divalent cations of larger ionic radius. Zn++ ion introduces an absorption band at 272 nm. Z1 centres are produced during irradiation but are destroyed upon F bleaching. The V band at 225 nm is very sensitive to F bleaching. The TL glow peak at 90 °C is the only predominant glow peak and it increases with X‐ray dosage. F bleaching reduces this peak and induces a strong one at 125 °C which is a weak shoulder in the unbleached crystal. Only one strong intrinsic emission appears at 425 nm in TL spectra, X‐ray luminescence, and MTL. Other intrinsic emissions are either very weak or are absent. These results are discussed in the light of electron trapping by the impurity and the I‐V complexes of nn and nnn separations it introduces in the crystal.
Kinetics of Surface Segregation in Binary Alloys
Authors: Wille L. T. , Vennik J. 
Published: July 2007

AbstractA new theory for the kinetics of surface segregation in binary alloys is proposed, which takes into account the concentration in the subsurface layers. This more realistic segregation profile is derived within the regular solution pair‐bonding model. The surface composition as a function of time is determined analytically and it is in qualitative agreement with the experimentally observed behaviour.
Lattice Vibrations of V2O5. Calculation of Normal Vibrations in a Urey‐Bradley Force Field
Authors: Clauws P. , Broeckx J. , Vennik J. 
Published: July 2007

AbstractA normal coordinate analysis of the vibration spectrum of crystalline V2O5 is carried out in the assumption of a Urey‐Bradley force field. The calculated frequencies are adjusted to 29 experimental infrared and Raman frequencies by an automatic force constant refinement program. Analysis of the potential energy distribution and the atomic displacements allows the classification of the modes into nine types of oxygen vibrations and three types of chain modes. A discussion is given of effective charges and infrared intensities. An assignment of the infrared spectrum of polycrystalline V2O5 is added.
Resonant Scattering of Phonons in ZnS:Fe2+ and CdTe:Fe2+
Authors: Ram P. N. , Bijalwan R. D. , Semalty P. D. , Israel M. 
Published: July 2007

AbstractThe lattice thermal conductivity of ZnS :Fe2+ and CdTe: Fe2+ is analysed on the basis of Callaway's formalism with an emphasis on resonant scattering of phonons from the magnetic levels of the Fe2+ ions. The resonant scattering of E‐mode phonons corresponding to the T1 → T3 transition and T2‐mode phonons corresponding to the T4 → T3 transition are found to be important. An expression of resonance phonon scattering rate due to Klein was used which incorporates temperature dependent widths as essentially the only adjustable parameters. The estimated widths in ZnS :Fe2+ are seen to be low while they are reasonable in CdTe: Fe2+. The calculated results are in reasonable agreement with the experimental data.
Temperature and Field Dependence of Exciton‐Magnon Absorption of NaMnCl3
Authors: Popov E. A. , Kotlyarskii M. M. , Edelman I. S. 
Published: July 2007

AbstractThe behaviour of the optical absorption bands of NaMnCl3, is experimentally studied in the region of the 6Alg → 4Alg, 4Eg(4G) transition of the Mn2+ ion in the temperature range 1.8 to 20 K and in magnetic fields up to 20 T. Exciton and its “hot” magnon sidebands are observed in the spectrum. The anomalous temperature dependence of the exciton‐magnon bands intensity is explained by participation of magnons with wave vector k ± o in absorption. The low energy exciton‐mag‐ non band is supposed to be due to simultaneous creation of an exciton and annihilation of three thermally created magnons.
Electronic Structure of the Cubic Laves Phase of γ‐CeAl2
Authors: Lopez‐Aguilar P. , Costa‐Quintana J. 
Published: July 2007

AbstractThe electronic structure of the cubic Laves phase of γ‐CeAl2, is performed by means of a selfconsistent first‐principles pseudopotential model which includes the Coulomb correlation (Cc) effects within the band Hamiltonian. The electronic structure without the pseudopotential is also calculated and both results are compared. The wave functions are determined of the electronic states with 4f character and their couplings with other extended states. The main features of the electronic structure of this Ce alloy consist in the existence of peaks corresponding to the different 4f configurations and the complex location of the occupied 4f bands (≈ 2.7 eV below the Fermi level). All these characteristics are quantitatively determined and are in good agreement with previous theoretical and experimental results.
Influence of Damping on the Energy Loss Straggling of Low Velocity Protons in an Electron Gas
Authors: Gras‐Marti A. , Anderson V. E. , Ritchie R. H. , Ashley J. C. 
Published: July 2007

AbstractWhen damping is included in an electron gas, an increase in the straggling parameter of low energy ions is predicted. The magnitude of this effect is estimated. The calculations provide a step forward towards a better understanding of experimental data on low energy straggling, which appears to be consistently higher than existing calculations based on the (undamped) free electron gas model. More experiments for low velocities would be desirable in order to check the theoretical predictions.
Non‐Equivalence Effects in Cluster Self ‐Consistent Calculations of Ionic Solids
Authors: Matos Maria , Maffeo B. 
Published: July 2007

AbstractA simple model is used to analyze actual cluster calculations and an interpretation of the existence of central levels well separated from band levels is proposed for INDO and Xα methods. The analysis shows that the convergence to the infinite solid through the use of a point charge boundary condition cannot in general eliminate this symmetry non‐equivalence effect, which is related to the approximate treatment of two‐electron interactions inherent to each kind of cluster method.
The Structure of the Magnetic Centre in Cs3CoCl5
Authors: Lukin S. N. , Teslya O. P. 
Published: July 2007

AbstractThe influence of mechanical deformation of the tetragonal crystal Cs3CoCl5, on the EPR spectrum of the Co2+ ion tetrahedral centres is studied. The contributions of two main mechanisms of forming of ground state zero‐field splitting (modifications of volume and “shape” of the magnetic complex) are separated. The calculated angle of the distortion of tetrahedral nearest environment of the paramagnetic ion (γ – γ0 = −0.8°) is in good agreement with the X‐ray analysis data. The correlation of sign of the tetrahedral magnetic centre distortion with the sign of the zero‐field parameter D is considered.
Thermoelectric Power Due to Small Polaron Hopping Motion in Disordered Systems
Authors: Triberis G. P. 
Published: July 2007

AbstractA theory is developed of the thermoelectric power associated with electronic phonon‐assisted hopping motion between energetically inequivalent sites with different electron–lattice interaction parameters. The general results are applied to the high‐temperature small polaron hopping case. Comparison is made with other theories.
Determination of the photoemission generation depth with use of experiments on the dynamic scattering of X‐Rays
Authors: Kruglov M. V. , Solomin I. K. , Lunev A. V. 
Published: July 2007

AbstractThe angular dependences of photoemission are measured in Bragg diffraction of X‐rays on germanium and silicon crystals covered with amorphous layers of various thickness. The function K(z) – the integral of electron escape probability versus generation depth – is obtained from the experimental data. The escape depth is found to be substantially lower than the estimates often used whereas K(z) is satisfactorily described by Liljequist's theory. In the photoeffect technique, the depth of the explored layer depends on the primary‐to‐secondary electron recording efficiency ratio. The capabilities of two methods of deep scanning – by changing the initial energy of electrons by a variation of the radiation wavelength and by means of the escape energy selection of electrons – are compared.
On SCCF theory of magnetic properties of 1‐D binary alloys (magnon spectrum, magnetization)
Authors: Šlechta J. 
Published: July 2007

AbstractA detailed SCCF calculation of the magnon densities of states of 1‐D binary alloys, both with statistical short range order and purely random ones, is presented and the results are compared with the electronic densities of states of those alloys. Also the demonstration of the higher spatial correlations (HSC) in the shapes of the magnon densities of states is discussed. It is shown that for some constitutions of 1‐D binary alloys the long range magnetic order is likely to exist and results for the temperature dependence of the magnetization of those binary alloys is also given.
Critical exponents of the magnetostriction in amorphous alloys
Authors: Vázquez M. , Hernando A. , Kronmüller H. 
Published: July 2007

AbstractThe magnetostriction of some amorphous alloys is investigated in the temperature range of the magnetic phase transition. Measurements are made with the help of a method described previously, and which is based on the observation of the macroscopical torsional strain under a longitudinal electrical current. The magnetostriction near the ferromagnetic phase transition is found to obey a (Tc – T)χ‐law with critical exponents depending on the type of alloy and values varying in the range of χ = 1.1 to 1.4.
Monte‐Carlo studies of energy straggling of electrons in solids
Authors: Kotera M. , Murata K. , Nagami K. 
Published: July 2007

AbstractAn energy straggling distribution is incorporated in the Monte‐Carlo simulation of keV‐electron scattering in solids. This distribution is obtained by modifying the original Blunck and Leisegang distribution based on the Landau theory. The average energy loss of the distribution is adjusted to fit the stopping power of the Rao Sahib and Wittry equation (the modified Bethe equation). Since an electron trajectory is simulated by a stepwise fashion, the energy straggling of an electron even in a bulk specimen can be calculated. By comparing with an experimental energy distribution of transmitted electrons from a thin film, the validity of the present model is discussed. The electron path length distribution in a bulk specimen due to the energy straggling is also discussed.
Plasmon bands in X‐ray spectra of polycrystalline beryllium
Authors: Papademetriou D. K. , Katsanos D. , Doukas A. G. 
Published: July 2007

AbstractThe plasmon bands are observed in the X‐ray spectra of polycrystalline Be, using CuKα1, SaL2 radiation for k > kc. The spectra show four peaks at the long wavelength region of Raman bands, assigned to the 3spxpy‐3spz splitting of the 3ps hybridized band.
The band structure of Co3Ga and Co2MnGa and the electrical conductivity of related alloys
Authors: Fletcher G. C. 
Published: July 2007

AbstractBand structure calculations are carried out for hypothetical nonmagnetic alloys Co2Ga and Co2MnGa and for the ferromagnetic alloy Co2MnGa, all with the L21 structure. The results are used to investigate the electrical conductivity of (Co, Ga) and Co(Ga, TM) alloys (where TM is a transition metal), particularly as this involves hopping conduction. Explanation of the latter by the presence of antistructure Co or TM atoms on the Ga subslattice seems to be confirmed although they do not affect normal conduction appreciably. Mn assists hopping conduction less than antistructure Co since it provides fewer good hopping states, albeit better ones.
Electronic properties of iron chalcogenides FeS, FeS2, FeSe2, and FeTe2
Authors: Singh O. P. , Gupta V. P. 
Published: July 2007

AbstractLavin's modifications of Phillips and Van Vechten (PVV) theory are discussed and hence ionic gap (Ec), homopolar gap (Eh), and ionicity (fi) are investigated for iron chalcogenides (FeS, FeS2, FeSe2, and FeTe2). A correlation between evaluated values of ionicity and Mossbauer isomeric shift is also discussed.
Solitary excitations in molecular chains in the presence of vibronic states
Authors: Pushkaeov Kh. I. , Peimatabova M. T. 
Published: July 2007

AbstractSolitary excitations due to the combination of an electronic excitation with intramolecular (both totally symmetric and nontotally symmetric) vibrations are shown to take place in molecular chains. Two cases are considered: a) when the molecules of the chain are fixed at their equilibrium positions and b) when the chain molecules are oscillating. In the second case solitary bound states of the chain deformation and the exciton‐intramolecular excitation can exist and propagate along the chain. The parameters of the solitons and the energy of the system are calculated.
Bond charge approximation for valence electron density in elemental semiconductors
Authors: Bashenov V. K. , Gorbachev V. E. , Marvakov D. I. 
Published: July 2007

AbstractThe spatial valence electron distribution in silicon and diamond is calculated in adiabatic bond charge approximation at zero temperature when bond charges have Gaussian shape and their tensor character is taken into account. Agreement between theory and experiment is achieved. For this purpose Xia's ionic pseudopotentials and Schulze‐Unger's dielectric function are used. By two additional parameters AB and Z′B the spatial extent is described of the bond charge and local‐field corrections, respectively. The parameter Z′B accounts for the ratio between the Coulomb and exchange correlation interactions of the valence electrons. Its silicon and diamond values have different signs.
Optical properties of EuF3 and GdF3 and paramagnetic susceptibility of EuF3
Authors: Jayasankar C. K. , Antic‐Fidancev E. , Blaise M. Lemaitre , Porcher P. 
Published: July 2007

AbstractThe optical properties of EuF3 and GdF3 are reinvestigated. Crystal field parameters derived from the data by using the D3h → C2v descending symmetry procedure for EuF3 are (in cm−1): B = 465, B = 375, B = −232, B = −96, B = −114, B = −490, B = 83, B = −518, B = −162. The temperature dependent paramagnetic susceptibility of EuF3, is calculated by using the simulated wave functions. The calculated and experimental paramagnetic susceptibilities are in very good agreement.
15N‐NMR investigations of dynamical processes near the ferroelectric phase transition of TSCC
Authors: Engelke F. , Michel D. , Windsch W. , Petersson J. 
Published: July 2007

Abstract15N‐NMR measurements are performed to investigate the proton dynamics in the hydrogen bonds of type NH … Cl near the ferroelectric phase transition (Tc = 130 K) of tris‐sarcosine calcium chloride (TSCC), enriched with 15N nuclei. In the ferroelectric phase the second moment and the shape of the 15N‐NMR lines change significantly with decreasing temperature. The experimental data can be explained on the basis of a quantum, mechanical torsion oscillator model for the NH2 group. This interpretation allows the definition of a local order parameter from the NMR spectra which changes with the temperature at T < Tc similarly as the spontaneous polarization.
Multiple scattering approach to the XANES theory of alkali halide crystals. II. Band structure approach and cluster approximations
Authors: Datsyuk V. N. , Gegusin I. I. , Vedrinskii R. V. 
Published: July 2007

AbstractThe conduction band structures of six alkali halide crystals (LiF, NaF, KF, LiCl, NaCl, KCl) are studied by means of the augmented plane wave method (APW). The local partial densities of states (LPDOS) and X‐ray absorption K‐spectra are calculated. The band structure predictions are compared with the results of cluster model calculations obtained within the framework of a Green's function approach employing multiple scattering technique. The effect of cluster size is examined for the clusters containing various numbers of atoms. It is shown that 57‐atom clusters are sufficiently large to represent the band results in XANES region. The hole effect is exhibited as the intensity redistributions and the shifts of the peak positions, although more serious changes in the case of Li K‐spectrum in LiF are found.
Electron tunneling from an ultrathin quantum well in constant and alternating electric fields
Authors: Kundrotas J. , Dargys A. 
Published: July 2007

AbstractThe change of electron tunneling probability with time after instantaneous application of an electric field is calculated for a one‐dimensional ultrathin quantum well (QW). The electronic wave function bound to such QW is characterized by relatively large exponential tails on both sides of the QW. By solving the time dependent Schrödinger equation exactly, it is demonstrated that the tunneling rate is substantially larger than that predicted by standard approximations. This property may appear useful in constructing new ultrahigh‐speed solid state devices based on isolated QWs.
Amorphous ferromagnets with two magnetic components A BPW approximation
Authors: Áwiderczak K. , Zagórski A. , Król J. 
Published: July 2007

AbstractThe influence of chemical short‐range order (SRO) on the Curie temperature and magnetic susceptibility is examined for a model amorphous ferromagnet consisting of two kinds of magnetic atoms (SA = 1/2 and (SB = 2). A Bethe‐Peierls‐Weiss‐like approximation (BPW) is used for the classical Heisenberg model. A strong dependence of TC on SRO is established.
Band and branch inversion phenomena in GaAs–AlxGa1–xAs superlattices
Authors: de Digs Leyva M. , Sabin J. , Gondae J. López 
Published: July 2007

AbstractA detailed analysis of the symmetry properties of the Bloch envelope functions in GaAs–AlxGa1–xAs superlattices (SL) for finite values of k⟂ is made. It is pointed out that in the (E, k, k⟂) space, where k is the SL wave vector, the energy spectrum is built up of independent branches. Each one of these branches contains two curves of definite parity placed at the planes k = 0 and k = π/d, where d is the SL period. It is shown that with increasing magnitude of k⟂, an interchange of symmetries between branches (similar to the well known band inversion phenomenon) may occur at the plane k = 0 or k = π/d. Furthermore, it is also shown that a magnetic field may induce interchange of symmetries between contiguous bands.
Effect of chemical and spin disorder on shallow impurity states in semiconductor alloys
Authors: Mycielski J. , Witowski A. M. 
Published: July 2007

AbstractThe effect of chemical and spin disorder in semiconductor alloys, in particular in semimagnetic semiconductors (diluted magnetic semiconductors), on shallow donor states is discussed in detail. Assuming short‐range composition and spin correlations, and the isotropy of spin–spin interaction, the averages of products of the matrix elements of the disorder Hamiltonian are calculated. The theory is applied to the problem of ground‐state spin‐splitting and spin‐flip transitions, as well as to Is → 2s transitions.
Optical absorption of EL20 and EL2+ in semi‐insulating GaAs: Cr
Authors: Ulrici W. 
Published: July 2007

AbstractThe analysis of the optical absorption spectra of semi‐insulating GaAs: Cr measured at T = 78 K before and after illumination with light quenching the absorption due to EL2 centres shows that besides Cr2+, Cr3+, and filled (EL20) deep‐donor centres also empty (EL2+) centres may be present. These EL2+ centres cause an optical absorption with spectral shape in accordance with the photoionization cross section σp. The optical quenching of EL2+ is connected with an increase of [Cr3+] by hole capturing. A procedure is proposed to evaluate [EL20], [EL2+], [Cr2+], and [Cr3+] from the optical absorption spectra.
About the role of surface scattering of electrons in the theory of the anomalous acoustic skin‐effect
Authors: Ivanovski G. J. , Galbova O. 
Published: July 2007

AbstractThe effect of transformation of electromagnetic into weakly attenuated acoustic waves is studied in massive metal samples. The role of the δ‐shaped surface force is estimated which occurs under diffuse reflection of the conduction electrons. The study is performed with an arbitrary coefficient of electron reflection and in absence of a constant magnetic field, when the deformation mechanism of transformation is primary.
Lattice dynamics of solid N2O
Authors: Shibata Y. , Ishi K. , Takahashi S.‐I. 
Published: July 2007

AbstractThe lattice dynamics of the molecular crystal N2O is treated throughout the Brillouin zone within the framework of classical harmonic approximation. By using the Kohin type potential, dispersion curves, density of states, and heat capacity at low temperatures are obtained. The results are in good agreement with available experimental data. It is also shown that the lattice frequencies of the isomorphous crystal CO2 calculated by using the same potential agree well with neutron scattering data.
Electron structure and phase diagrams of low‐temperature rare‐earth magnets
Authors: Mitsek A. I. , Yu. Guslienko K. , Pavlovskii S. V. 
Published: July 2007

AbstractThe transition ion states are described by mixed many‐electron operators. The hybridization coefficients are calculated by the variational principle. Low‐temperature magnets are considered within the weak‐exchange energy limit. The destruction of the magnetic order is studied at the increase of the single‐ion anisotropy and (Ising's) exchange anisotropic energy. The magnetic phase diagrams (MPD) of the uniaxial and cubic magnets are calculated. The restrictions of the moment value J and anisotropy constant k at which these critical phenomena occur are determined here. The influence of superconductivity (SC) on the MPD is studied. An enhancement of SC is shown in the antiferromagnetic state. The intermediate helix phase is studied between the SC and ferromagnetic states.