bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Anisotropy of Scattering in Doped n‐Ge at Low Temperatures
Authors: Matveev G. A. , Tsidilkovskii I. M. , Lonchakov A. T. 
Published: July 2007

AbstractOn Ge : Sb crystals with dopant concentrations, N, ranging between 8 × 1016 and 1.5 × 1018 cm−3, the temperature and concentration dependences are found of the mobility anisotropy coefficient, K, over the temperature interval 4.2 K ≦ T ≦ 180 K and at T ≦ 4.2 K. At temperatures Tc close to the Hall‐coefficient‐maximum temperature, the K versus T curve exhibits a minimum at T = Tmin. The temperature Tmin corresponds to the boundary that separates the regions of weak and strong electron scattering. At sufficiently low temperatures, where the scattering is strong (the impurity and band states of electrons are mixed), neither the formulae for classical conductivity nor the formulae of the theory of quantum corrections permit a reliable determination of the value of mobility anisotropy K.
Ashcroft‐Langreth Prescription for Effective Core Diameter in Liquids. A Variational Analysis
Authors: Das T. , Bhuiyan L. B. , Joarder R. N. 
Published: July 2007

AbstractThe Ashcroft‐Langreth (AL) ansatz for the effective hard‐sphere diameter in a simple liquid is analysed in the light of Gibbs‐Bogoliubov variational theory for the free energy of the system. It is seen that for a reasonable choice of the pair potential, for example, the Lennard‐Jones potential for liquid Ar and the effective pair potential based on the Ashcroft model for liquid alkalis, Na, K, Rb, and Cs, the prescription is in general valid at or near the normal melting temperatures. However, at the thermodynamic states away from the normal melting point, the ansatz becomes increasingly inaccurate.
First‐Principles Calculation of the Lattice Dynamics of the Co0.92Fe0.08 Alloy
Authors: Shyam R. , Upadhyaya S. C. , Upadhyaya J. C. 
Published: July 2007

AbstractFirst principles calculation of the lattice dynamics of the f.c.c. Co0.92Fe0.08 alloy is done by applying the transition metal model potential of Animalu. The ab initio radial and tangential force constants are calculated upto 10th nearest neighbours for pure Co and Fe at the lattice constant of the f.c.c. alloy. Next concentration averages of the force constants and masses of Co and Fe are used to compute the phonon frequencies of the Co0.92Fe0.08 alloy. A reasonably good agreement is found between the computed and experimental dispersion results. Phonon density of states, specific heat, Debye temperature, and elastic constants are also computed and the results are compared with available calculations of others.
Electron–Hole Exchange Interaction of Excitons in Direct Band Gap Cubic Semiconductors with Degenerated Valence Band
Authors: Huong Nguyen Que , Thang Nguyen Toan , Viet Nguyen Ai 
Published: July 2007

AbstractFine structure of excitons in direct band gap cubic semiconductors is studied. The general formulae for exchange energy of any excitonic states are given. Splitting of energy levels and corresponding wave functions are written for nS and nP exciton states for example.
The Electronic Structure of the Alkaline‐Earth Oxides. V. Peculiarities of the Hole‐Trapping in NaF and MgO
Authors: Lobatch V. A. , Rubin I. R. , Lushnikov P. V. 
Published: July 2007

AbstractCalculations are made for clusters simulating the Vk‐center in NaF and a hypothetic self‐trapped hole in MgO within the embedded cluster approach. The “non‐ionic” charge configuration of MgO, described earlier, is analysed as a possible cause of the absence of the hole self‐trapping manifestations in the oxide according to the mechanism known for NaF. Due to the delocalization of oxygen 2p‐states the hole orbital is oriented, in contrast to NaF, perpendicularly to the 2‐anion quasi‐molecule axis, while the hole state itself lies close to the top of the potential barrier bonding this state.
The Thermoelectric Figure of Merit in the Mixed Crystal System p‐(Bi1−xSbx)2Te3
Authors: Stordeur M. 
Published: July 2007

AbstractThe figure of merit Z is a measure for the effectiveness of the thermoelectric material p‐(Bi1−xSbx)2Te3and depends on the valence band structure, the charge carrier scattering, the lattice thermal conductivity, and the free carrier density. It is shown that crystals with the compositionx= 0.75 are favoured by the band structure to have the highest figure of merit in this mixed crystal series. In the frame of a consistent model for the electronic structure the theory—experiment comparison gives good quantitative agreement for theZ(S)‐plot in terms of effective masses and lattice thermal conductivity over a wide range of the Seebeck coefficientS.
Bloch Walls in Magnetostrictive Metallic Glasses
Authors: Kraus L. 
Published: July 2007

AbstractOne‐dimensional Bloch walls in weakly anisotropic magnetostrictive media are investigated theoretically. It is shown that there are two effects of magnetoelastic coupling on the walls: 1. magnetic anisotropy induced by external stress and 2. internal stress of the wall required by compatibility. The resulting magnetic anisotropy is generally of orthorhombic symmetry implying that the wall energy depends on the orientation of the wall. The internal stress of the wall can be a determining factor for the energy and the width of the walls in weakly anisotropic and highly magnetostrictive amorphous alloys.
Lattice Dynamics of Ammonia
Authors: Zeng W. Y. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is developed and applied to the vibrations of solid ammonia, NH3 and ND3. Four intramolecular (two stretching and two bending) and six intermolecular force constants are adjusted to obtain the best fit to the crystal field splittings and lattice mode frequencies observed by Raman and infrared spectroscopy. Isotopic shifts are also calculated. The principal intermolecular interactions are of the HH and NH type, but there is no evidence of hydrogen bonding in the crystal. The intramolecular N–H bond is weakened by about 8% from its gas phase value.
Mobilities and Concentrations of Charge Carriers in Polycrystalline Bi0.87Sb0.13 Films
Authors: Völklein F. , Dillner U. 
Published: July 2007

AbstractThe carrier mobilities and concentrations of polycrystalline films of Bi0.87Sb0.13 with thicknesses between 30 and 330 nm are presented and discussed in the temperature range between 80 and 360 K. They are calculated from the electrical conductivity as well as the low‐field Hall and magnetoresistance coefficients in a magnetic field directed orthogonally to the film plane. An anisotropic two‐carrier model is taken as a basis for the calculation.
Theory of Germanium‐Related Defects in Vitreous Silicon Dioxide. I. Germanium Atom in Silicon Site
Authors: Dianov E. M. , Sokolov V. O. , Sulimov V. B. 
Published: July 2007

AbstractA germanium substitutional impurity (Ge atom in a silicon vacancy) in vitreous silicon dioxide is investigated by a quantum chemical MNDO method in a cluster approach taking into account the relaxation of the nearest atomic environment of the defect.
Temperature Dependent Field Ionization of Phosphorus Atoms in Silicon
Authors: Dargys A. , Žurauskienė N. , Žurauskas S. 
Published: July 2007

AbstractTemperature dependent transient tunneling spectra of Si〈P〉 are considered on the basis of two models. The influence of sound vibrations on the field ionization of phosphorus atoms in silicon is analysed numerically and compared with available experimental data. It is found that eletron thermal transitions from ground to orbit‐valley split levels and their subsequent tunneling through the barrier with lower potential gives the main contribution to the ionization rate of phosphorus atoms at high electric fields.
Resistive Wires Instead of Ideal Leads. Breakdown of the Channel Equipartition Rule
Authors: Lenk R. 
Published: July 2007

AbstractA quantum wire with constant cross‐section and ideally reflecting lateral boundaries, filled uniformly (on the average) with point‐like elastic scatterers in the dilute limit, is considered as an idealized model of a resistive lead. Due to the unavoidable energy and channel dependence of the mean free path, the conducting channels contribute differently to the current which is dominated by the fast channels. This result disagrees with the usual channel equipartition rule for ideal leads fed by reservoirs in statistical equilibrium. The nontrivial behaviour of the mean free path prevents also the employment of separate chemical potentials, in the strict sense of corresponding partial equilibrium states, for the carriers moving in both directions within a current‐carrying wire.
EPR of a Gd3+‐Doped NH4Pr(SO4)2 · 4 H2O Single Crystal. Study of Phase Transition and Superposition Model Calculation of Zero‐Field Splitting Parameters
Authors: Misra S. K. , Sun Jiansheng 
Published: July 2007

AbstractX‐band EPR spectra of a single crystal of Gd++‐doped NH4Pr (SO4)2 · 4 H2O (APST) are recorded in the temperature range 4.2 to 410 K. The angular variation of the EPR line positions indicates the presence of two magnetically‐inequivalent Gd3+ ions. The orientations of their principal axes are determined. The Gd3+ spin‐Hamiltonian parameters are evaluated using a rigorous least‐squares‐fitting procedure. The superposition model is applied to calculate the values of the zero‐field splitting parameters b, b of Gd3+, and those of the intrinsic parameters b2 and b4. The temperature variation of the EPR spectra reveals the occurrences of two first‐order phase transitions in APST crystal at 266 and 155K.
Exciton Reflection Spectra of NaI Crystals. Effect of Surface Irradiation by Photons and Incidence Angle Dependence
Authors: O'Connel‐Bronin A. A. , Treshchalov A. B. 
Published: July 2007

AbstractReflection spectra of NaI crystals cleaved in liquid helium are investigated in detail. A fine structure is discovered in the spectral region adjacent to 2S exciton resonance at the high‐energy side. It is interpreted as the manifestation of the splitting of the n = 2 exciton state which was predicted by Balslev. The LO structure below the 2S line is observed, which is interpreted as the revealing of vibrational states of self‐trapped excitons. The influence of irradiation by photons on the crystal surface is studied. Considerable changes are detected in the 2S reflection line region, which are discussed involving the “dead” layer model. The character of the dispersion contour of the 2S exciton line is discussed. The dependence of the reflection spectrum on the incidence angle is investigated. A stronger angular dependence in the 2S region of the spectrum than in the 1S region is pointed out.
Dipole Polarizability of O2− Ions near the (011) and the (111) Surface of Alkaline Earth Oxides
Authors: Kassim H. A. 
Published: July 2007

AbstractThe effect of (011) and (111) surfaces on the dipole polarizability of O2− ions in alkaline earth oxides is estimated by employing a variational perturbation method in the manner of Kirkwood, Pople, and Schofield. Initially the study concentrates on O2− ions in the bulk and then moves gradually to surface sites. The reduced surface polarizability as compared with the bulk value is attributed to the variation in the crystalline medium when moving from the bulk to top layers. In all the cases, ideal surfaces are assumed. Modifications in these surface values due to surface reconstruction may be important but are not included in the present study due to the uncertainty in the actual surface geometry.
Nonequilibrium Thermoreflectance Evolution of Laser Irradiated Noble Metals
Authors: Wenschuh U. , Heiner E. 
Published: July 2007

AbstractA theory for the evalution of the optical properties of laser irradiated noble metal layers in a thermalized nonequilibrium stage presented recently is applied to the calculation of transient thermoreflectance alterations in gold, silver, and copper. An improvement of the theory that simplifies direct comparisons with experiments is given after the introduction of the laser intensity into the interacting term of the model Hamiltonian which describes the coupling of the laser field to the electron system. Numerical results are discussed in view of new time‐resolved pump‐probe‐experiments.
Structural Modelling of Low‐Symmetry Phases of Spinels. II. Phases with 1:3 Octahedral Order
Authors: Talanov V. M. 
Published: July 2007

AbstractOn the basis of the phenomenological theory of phase transitions the structural mechanism of ordering of octahedral cations of the type 1:3 in spinels is studied. With the help of the basic functions of the active six‐dimensional irreducible representations of the group Fd3m the structure of the ordered phase is deduced theoretically from the non‐ordered phase. The qualitative pictures of possible displacements of atoms near the temperature of the phase transition are given. The existence of isostructural modifications of the ordered structure is predicted.
X‐Ray Analysis of Structural Defects in a Semiconductor Superlattice
Authors: Holý V. , Kuběna J. , Ploog K. 
Published: July 2007

AbstractThe structural defects in a (GaAs)m/(AlAs)n superlattice are studied experimentally and theoretically as well. Three models for the defects are proposed, which follow from the SL growth kinetics. Direct expressions for the reflectivities are derived from the semikinematical approximation of X‐ray diffraction, assuming that the statistical parameters characterizing the defect models are distributed normally. On the basis of a numerical fit of the theoretical and experimental double crystal X‐ray rocking curves the mean lattice parameter and the mean chemical composition as well as their statistical dispersions are found for a [(GaAs)m/(AlAs)n]120 superlattice. The X‐ray diffraction curves enable one to find the most probable model for the actual structural defects in the real superlattice.
Transient Thermoelectric Effect in Quasi‐Two‐Dimensional η‐Mo4O11 Crystal
Authors: Sasaki M. , Tai G. X. , Inoue M. 
Published: July 2007

AbstractDynamic measurements of thermal diffusion of conduction carriers in quasi‐two‐dimensional η‐Mo4O11 crystals which undergo charge‐density‐wave transitions are made over the temperature range 12 to 300 K and time range 50 ns to 2 ms using a pulsed laser‐induced “transient thermoelectric effect (TTE)” technique. The light‐generated TTE voltage decays exponentially with multiple relaxation times τi (i = 1 to 5), from which the nature of the Fermi surfaces of both electrons and holes is discussed based on recent tight‐binding band calculations.
Positron Studies of the Chemical Composition of Guinier‐Preston Zones in AlZn Alloys
Authors: Dlubek G. , Gerber W. 
Published: July 2007

AbstractVarious decomposed AlZn alloys are investigated by positron lifetime and angular correlation technique in order to study the potential of positron method in estimating the composition of Guinier‐Preston zones. From experiments the curve shape parameters, S, the core annihilation rate, λc, and the number of free conduction electrons, z, derived from the zeros of the one‐dimensional Fourier‐transform of the angular correlation curve are estimated. The response of the various annihilation parameters to zone composition, positron affinity, and alloying effects (lattice change, charge transfer) is discussed. The number of free electrons per atom reflects most clearly the chemical composition of the GP zones.
Electron Mobility for a SiSi1−xGex Quantum Well: Acoustic Phonon Scattering Mechanism
Authors: Tutor J. , Bermudez J. A. , Comas F. 
Published: July 2007

AbstractDrift mobility is calculated at the low temperature regime along the Si channel of a SiSi1−xGex quantum well (QW). Boltzmann transport theory is applied assuming electron interaction with acoustic phonons via the deformation potential mechanism. Infinite potential barriers are supposed at the interfaces and the electron states are obtained in the effective mass approximation. The acoustic phonon spectrum is treated in the standard 3D approach using an electron–phonon Hamiltonian adapted from the bulk case. Obtained results are compared with experiment.
Frequency Dependednt Losses in YBaCuO Superconductors
Authors: Nag A. , Joarder R. , Ghosh B. , Neogy C. , Deb S. K. 
Published: July 2007

AbstractThe real and imaginary parts of the frequency dependent response of YBaCuO samples doped with scandium are measured over a wide frequency range (5 Hz to 13 MHz) both, in the normal (at 298 K) and in the superconducting (at 77 K) states. An attempt is made to made to identify the relaxation mechanisms responsible for ac conduction in the samples. It is suggested that 2p hole‐polarons associated with the oxygen atoms play an important role in determining the frequency dependent behaviour in the normal state as well as at their superconductivity.
Properties of p‐Polarized Nonlinear Surface Polaritons
Authors: Groza A. D. , Strizhevskii V. L. 
Published: July 2007

AbstractA solution is obtained of the stationary problem of p‐polarized nonlinear surface polaritons (NLSP) near the interface of two media, one of which is optically linear and the other one has an optical nonlinearity with saturation. On this base the properties of the NLSP propagating along the interface of the self‐focusing medium with positive dielectric fanction and the linear medium with positive dielectric function are investigated in detail.
Computer Simulations of ESR Spectra of Amorphous Thiomolybdates
Authors: Berger R. , Haddad M. 
Published: July 2007

AbstractESR spectra of amorphous chalcogenides MoS2+x (1 ≧ x ≧ 0) at 9.5 and 35 GHz reveal three different signals whose parameters are determined by computer simulation. The corresponding paramagnetic centers are: a) an electron hole center, with three principal values of the g‐tensor, localized on a sulfur atom, b) a Mo(V) center surrounded by sulfur atoms and characterized by an axial g‐tensor, c) a Mo(V) center surrounded by oxygen atoms, with also an axial g‐tensor, which results from a contamination by oxide traces. An anisotropic linewidth is taken into account to obtain an acceptable fitting for the different signals, it means distributions of g‐values originating from random local structural fluctuations in the amorphous compounds. Amorphous Li2MoS3 is also examined by ESR for comparison.
Shear Instability in a System of Point Defects
Authors: Gluzman S. L. , Psakhe S. G. 
Published: July 2007

AbstractImpurity behaviour (both thermodynamic and mechanic properties) are investigated under pressure and shear application. The conditions are found of shear instability occurrence — the critical temperature θc and critical shear stress τc. θc decreases with shear stresses application and τc decreases with temperature growth. The used Green's functions method could be applied for the different cases of atomic Hamiltonians and for the different types of mechanical loading.
Orientationally Disordered Hydrogen. Freezing of Short‐Range Order
Authors: Kokshenev V. B. 
Published: July 2007

AbstractThe RMS (root mean square) polarization magnitude of an orientationally disordered ortho‐parahydrogen mixture is analyzed in terms of a microscopic model. Various models of the quadrupolar glass theory are considered; the calculated orientational polarization values are compared with the data of the NMR absorption signal in hydrogen. It is found that fluctuations of the ortho‐hydrogen molecule crystalline field produce an essential effect on freezing of the short‐range orientational order at temperatures above 1 K.
Luminescence of Lead Ions Associated with Interstitials and Vacancies in Alkali Halides
Authors: Egemberdiev Zh. , Usarov A. , Zazubovich S. 
Published: July 2007

AbstractSeveral types of luminescent associates of lead ions (Pb2+, Pb+) with interstitial halide ions (X−i) as well as with cation (v−c) and anion (v+a) vacancies are observed in alkali halides X‐irradiated at 80 or 295 K. Optical properties and a detailed structure of these associates, the processes of their creation and destruction as well as their optically or thermally stimulated transformations are studied. The associates investigated form the three following groups each containing several types of centres: (1) centres on the basis of a PbX‐molecular ion; (2) centres on the basis of a Pb2+X dipole; and (3) centres of the laser‐active structure on the basis of a Pb+X−v+a associate. The optical characteristics of the various centres of each group are shown to be similar. It is concluded that they are determined by electronic transitions between the energy states of the basis associate (PbX, Pb2+X, or Pb+X−v+a), and that the influence of some other defects (v, X, X3, etc.) may be considered as a small perturbation.
A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals
Authors: Prasad P. S. S. , Radhakrishna S. 
Published: July 2007

AbstractThe optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient (300 K) and liquid nitrogen temperatures (80 K). From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for the Co2+ ions in the crystals. The splittings observed for the 4T2g(F) band in Co2+ at 80 K is explained as due to the spin—orbit interaction. The band positions are fitted with the four parameters: B = 960 cm−1, C = 3840 cm−1, Dq = 940, and γ = 550 at 300 K and B = 990 cm−1, C = 3960 cm−1, Dq = 940, and γ = 600 at 80 K. The polarized crystal spectra of Co2+ doped 3 CdSO4 · 8 H2O are recorded at 80 K and the three anisotropic bands observed near 8097, 14422, and 18692 cm−1 are presumed to be due to the spin allowed 4T1g(F) → 4T2g(F), 4T1g(F) → 4A2g(F), and 4T1g(F) → 4Tlg(P) transitions of substitutional Co2+ in 3CdSO4 · 8H2O. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole in nature.
Crystal Field in Some Rare Earth Intermetallics Analysed in Terms of the Superposition Model
Authors: Diviš M. 
Published: July 2007

AbstractThe reliable experimental data of the crystal field parameters in the REPd3 (RE = Pr, Nd, Tb, Dy, Ho, Er, Tm), (RE, Y)Pd3, REB6 (RE = Pr, Nd), PrX2 (X = Ni, Rh, Ir, Pt, Ru, Mg), RENi2, (RE, T)Al2 (T = Sc, Y), and RENi5 intermetallic compounds are analysed in terms of the superposition model. The obtained systematic behaviour of intrinsic parameters supports the applicability of the model in RE intermetallics. The validity of the usual power‐law expression, connection with the results of ab‐initio calculations, and further possible tests of the model are discussed.
Some Magnetic Properties of Thin Ferromagnetic Film with Enhanced Surface Exchange Interactions
Authors: Wiatrowski G. , Mielnicki J. , Balcerzak T. 
Published: July 2007

AbstractThin S = 1/2 ferromagnetic film with exchange interaction enhanced near the film surface is considered in the Ising model. As a result the phase diagrams, the magnetization profiles, and magnetization curves for several particular cases are presented. A modified definition of the critical δc parameter for the thin film case is also proposed.