bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescent Associates of Pb2+vc− Dipoles with Interstitial Iodine Atoms in KI:PbI2 Crystals
Authors: Egemberdiev Zh. , Ismailov K. , Usarov A. , Zazubovich S. , Jaanson N.
Published: July 2007

Two infrared emission regions (with maxima at 0.803 and 0.723 eV) recently observed by Harami et al. in X‐irradiated KI:PbI2 and the emission regions with maxima at 2.01, 1.79, and near 1.2 eV are studied. The observed emission bands are connected with Hz(Pb2+) centres (Pb2+ ions associated to [I2−]ac molecular ions on anionic (a) and cationic (c) sites). The infrared emission bands of these centres are due to processes occuring in the excited state of the [I2−]ac molecular ion perturbed by the Pb2+ ion. The emission bands are connected with electronic transitions from the tetragonal (2.01 and 1.79 eV peaks) and trigonal (region around 1.2 eV) minima of the triplet relaxed excited state of the Pb2+ ions perturbed by the [I2−]ac ion which can occupy two different positions with respect to Pb2+. The emission band with maximum at 2.05 eV and the region near 1.2 eV are associated to similar transitions in the Pb2+ ion perturbed by the [I3−]aca (V2z(Pb2+) centres) molecular ion. On the basis of these results the optical properties of VL centres (at 0.805 and 0.734 eV), previously observed by Harami et al. in halogen‐excess KI crystals, and assumed here to be the [I2−]ac molecular ions, are also discussed.
On the Quasichemical Model of Oxygen Absorption and Ordering in a High Temperature Superconductor YBa2Cu3O6+x
Authors: Andreev L. A. , Nechaev Yu. S. , Kalashnikova E. A. , Konovalov N. T. , Lykhin V. A. , Mineav Yu. A. , Olshevskii N. A.
Published: July 2007

In the framework of the quasichemical Williams‐Bragg model an equation is obtained for the isotherm of gas absorption by the interstitials of the solvent lattice with the effect of ordering recognized; the equation is applied to analysis and interpretation of experimental data on oxygen absorption and ordering in superconducting YBa2Cu3O6+x ceramics. The oxygen absorption in both, tetragonal and orthorhombic structures is described by an absorption isotherm which fits the Langmuir equation. Extreme concentratios of the “absorption centers” are found as the oxygen absorption energy and entropy in the tetragonal (T) and orthorhomic (O) phases. The ordering of absorbed oxygen is shown to be unrelated with the “oxygenoxygen” pairwise interaction and is attributable to the “T → O” transition. The experimental isotherms of oxygen absorption by the ceramics lead to elements of the “temperature–concentration (X)” phase diagram which characterize the boundary between the T‐ and O‐phase regions.
Low Temperature Absorption Spectrum of LiNiPO4
Authors: Belletti A. , Borromei R. , Cammi R. , Cavalli E.
Published: July 2007

The polarized absorption spectrum of LiNiPO4 crystals is investigated in the range 5000 to 25000 cm−1 at 9 K. The splitting and intensities of the bands in different polarizations are interpreted mainly in terms of a C2v perturbation of the octahedral site. The energies of the transitions are reproduced by means of a ligand field calculation, in which only a Oh → C2v site perturbation is considered, assumed as preponderant in the symmetry descent Oh → C2v → Cs.
Model Dielectric Constants of InSb
Authors: Miyazaki T. , Adachi S.
Published: July 2007

A calculation of the real (ϵ1) and imaginary (ϵ2) parts of the dielectric function of InSb between 0.0 and 6.0 eV in the temperature range 100 to 650 K is presented. This model includes the E0, E0 + Δ0, E1, E1 + Δ1, E'0, E'0 + Δ'0, E2 and E'1 gaps as the main dispersion mechanisms. The model is also made to account for the excitonic effects at the E1 and E1 + Δ1 critical points (CP's). The lineshape of the optical spectra obtained from this model is in satisfactory agreement with the experimental data over the entire range of photon energies. The temperature dependence of the strength and the broadening parameter at each CP are also given and discussed.
Tunneling‐Assisted Photon Emission in MIM Junctions
Authors: Volkov R. A. , Chuiko A. F.
Published: July 2007

Analytical expressions for the intensity of light emission associated with the inelastic tunneling of electrons in sandwich structures are obtained for semiclassical and quantum‐mechanical descriptions of the electron gas in electrodes. It is shown that in the quantum case the light intensity and currents of elastically tunneling electrons depend on the longitudinal density of electron states in the cathode and anode. Consideration is given to MIM junctions with crystallogrphically oriented electrodes exhibiting density peaks of free and occupied states near the Fermi levels. To increase the spectral intensity of the tunneling‐assisted photon emission in MIM junctions, it is proposed to use the electrodes made of such transition metals as Ni, Co, Mn, Ti, Fe, as well as of Pt and β‐NiAl which possess the above features.
Thermal Properties of TmGa3
Authors: Czopnik A. , Mädge H. , Pott R.
Published: July 2007

Heat capacity and thermal expansion of TmGa3 single crystal are reported. At low temperatures in comparison to TN the heat capacity and thermal expansion coefficient have a T3 exp (– Δ/T) dependence with an energy gap Δ in the spin‐wave spectrum equal to 1.15 K. In the paramagnetic state the crystal‐field contribution to the thrmal properties of TmGa3 is analysed.
Eigenproblem of Standing Spin Waves in a Multilayer Film with Inhomogeneous Interlayers
Authors: Maciejewski W.
Published: July 2007

A difference equation approach to standing spin waves in a multilayer film with inhomogeneous interlayers is developed. An exact procedure of solving the eigenvalue problem of dynamical matrix by its formal reduction to a small set of linear homogeneous equations is proposed. The effective parameters suitable for the study of the spin wave spectra and the spatial behaviour of the spin wave modes are introduced.
Raman Spectroscopic Study of Amorphous Pb5Ge3O11 and Its Crystallization
Authors: Lan Guo‐Xiang , Sun Hong‐Ye , Yin Zhi‐Ying , Wang Jing‐Yin , Wang Hua‐Fu
Published: July 2007

Amorphous Pb5Ge3O11 is prepared by single‐roller quenching. Internal vibrational modes of the GeO tetrahedra (and the Ge2O double‐tetrahedra) are observed in the Raman spectrum from amorphous Pb5Ge3O11. The Raman spectra of the sample annealed at 410 °C are different from that annealed at higher temperature. The results confirm the existence of a metastable phase in the crystallization process of amorphous Pb5Ge3O11. The Raman frequencies of stable crystalline Pb5Ge3O11 decrease with increasing annealing temperature, and this is attributed to the stress induced during crystallization.
Backscattering of Fast Electrons
Authors: Afanasev V. P. , Naujoks D.
Published: July 2007

The inelastic reflection of fast electrons is investigated on the base of the “invariant imbedding method”. The non‐linear term in the integral equation can be neglected owing to the strong anisotropy of elastic cross‐section of fast electrons. Using the Fokker‐Planck approximation and the Laplace transformation a simple analytical formula is found expanding the backscattering coefficient into a series of Legendre polynomials. It is shown that the results from the model are in good quantitative agreement with experimental data.
Special Features of Optical Properties of Ternary Alloys Ti(FexCo1−x)
Authors: Sasovskaya I. I.
Published: July 2007

Measurements are made of the optical characteristics: n, k, σ(ω), ϵ1 (ω), ϵ2 (ω) of the ternary pseudo‐binary alloys Ti(FexCo1‐x), 0.2 ≦ x ≦ 0.8 in the spectral range 0.07 to 4.96 eV. The results obtained are compared with the optical properties of the compounds TiFe and TiCo. It is shown that the change in the main absorption band (0.6 ≦ ħω ≦ 3 eV) over the series of alloys can be explained by the shift of EF relative to the special features (minima, peaks) of the density of states curves N(E). An additional low‐energy quantum absorption within 0.2 ≤ ħω ≤ 0.6 eV discovered in ternary alloys is explained by interband transitions between virtual bound states which are due to antistructural Fe atoms and are responsible for ferromagnetism in Ti(FexCo1−x).
Molecular dynamics of the frozen‐in glassy state of Ni80P20
Authors: Stepanyuk V. S. , Katsnelson A. A. , Szasz A. , Trushin O. S. , Nayak P.
Published: July 2007

A molecular dynamics approach is used for the dynamic structure simulation of the Ni80P20 glassy‐like system. Calculations are made considering the rapid cooling from melt and the effect of glass transition temperature. Comparison with the experimental data is given with a reasonable correspondence.
Self‐consistent statistical theory of surface properties of anharmonic crystals. I. Structural and dynamical properties of singular surfaces of F.C.C. crystals
Authors: Zubov V. I. , Tretyakov N. P.
Published: July 2007

A statistical theory of anharmonic crystal—vapour interfaces is developed based on the correlative unsymmetrized self‐consistent field method (CUSF). The nonlinear integral equations for the one‐particle probability densities of atomes near the solid surface and their self‐consistent potentials are transformed into the transcendental equations for the moments of the distributions. Their solution determines the lattice relaxation near the surface, the amplitudes of the anharmonic vibrations of atoms, their anisotropy, and the self‐consistent potentials as well. As an application the structural and dynamical properties of an f.c.c. crystal in which the nearest neighbours interact are studied.
Vacancy motion in magnesium oxide analyzed via the CNDO/2 cluster model
Authors: Skala L. , Kenkre V. M. , Weiser M. W. , Katz J. D.
Published: July 2007

The dynamics of vacancies in magnesium oxide are studied applying the CNDO/2 method to calculate the electronic properties of clusters both, with and without magnesium and oxygen vacancies. The potentials for vacancy motion are calculated and detailed information about the character of bonding in the neighbourhood of a vacancy is obtained. It is found that the potential for magnesium ion migration is more squared‐off than the potential for oxygen ion migration. The shape of the potential well is expected to have practical relevance in microwave‐driven ionic diffusion.
An evaluation of the R—T spin coupling parameter in the rare earth–transition metal intermetallics
Authors: Duc Nguyen Huu
Published: July 2007

For the purpose of the evaluation of the R—T spin coupling parameter, ART, an analysis of the Curie temperature is made for the rare earth—transition metal systems RmTn (R rare earth T = Fe, Co; m/n = 1/2, 1/3, 6/23, and 2/17) and some systems of recent and growing interest, such as R2T14B, RT11Ti, RT10V2 and their ternaries Rm(Co, Fe)n. Besides the enhancement of ART in the light rare earth compounds, the dependence of ART on the magnetic moment of the 3d electrons is presented.
Interband electronic Raman scattering in semiconductors induced by nonparabolicity
Authors: Ismailov T. G. , Nazanly R. A.
Published: July 2007

The interband electronic Raman scattering (IERS) of light in narrow‐gap semiconductors due to nonparabolicity is investigated in the framework of the two‐band Kane model. Bulk and size‐quantized thin film cases are considered in detail. The possibilities to determine the semiconductor parameters and also to investigate the semiconductor—semimetal (and vice‐versa) transition with the aid of IERS are discussed.
Interaction of Current Carriers with Local Moments in a Narrow Band
Authors: Anokhin A. O. , Irkhin V. Yu.
Published: July 2007

One‐electron Green's functions of a narrow‐band paramagnetic insulator are calculated within the framework of the s–d exchange and Hubbard models with strong correlations. The agreement with the 1/z‐perturbation theory is discussed for the approximations employed. It is demonstrated that the analytical properties of the retarded Green's functions are violated for simple approximations in the Hubbard model and the s–d model with a negative exchange parameter I (and, for self‐consistent versions, at any sign of I). Numerical results for the corresponding densities of states are presented.
Wave Vector Dependent Magnetooptics in Semiconductors Linear and Nonlinear Interband Transitions
Authors: De Salvo E. , Girlanda R.
Published: July 2007

A perturbative calculation, out of the electric dipole approximation, of the one‐ and two‐photon interband transition rates between the Landau levels of a semiconductor is presented. A gauge independent approach for the description of the radiation–matter interaction Hamiltonian is applied in the study. Comparisons with other naive models and experimental results are reported.
Chlorine Diffusion in CdTe
Authors: Sadaiyandi K. , Ramachandran K.
Published: July 2007

The experimental results of chlorine diffusion in CdTe reveal that the dominant mechanism for diffusion is through neutral defect pair such as [VCdVTe]*. Here, theoretical calculations are carried out for all the possible mechanisms such as single vacancy, single interstitial, neutral defect pair, and Frenkel defect pair. The results suggest that the most possible mechanism for Cl diffusion in CdTe is that through neutral defect pair, supporting the experiment.
Interatomic Potentials in Silicon
Authors: Mazzone A. M.
Published: July 2007

A study is made, based on molecular dynamics simulations, of the properties of interatomic potentials currently used to describe solid structures with covalent bonding. From these studies it appears that none of the available forms of potentials leads to a satisfactory description of bulk silicon.
Electronic Structure in Relation to the Reactivity of Nonstoichiometric AxMX2 Layered Compounds
Authors: Molenda J.
Published: July 2007

The data concerning the character of the discharge curve for various materials are collected and correlated with the microscopic electronic parameters such as the metal‐metal distances in the corresponding materials. On the basis of this correlation an electronic model of alkali metal ion intercalation into AxMX2 (A = Li, Na; M = V, Cr, Mn, Co, Ni; X = O, S, Se) cathode materials is proposed. The potential changes accompanying electrochemical intercalation are ascribed to the changes of the Fermi level position in the cathode material. Consequently, the step‐like shape of the discharge curve is linked with the step‐like shape of the density‐of‐states curve. Comparison of the actual metal–metal distance RM–M with the critical distance Rc given by Goodenough allows the prediction of the properties of oxide cathode materials. The materials for which RM–M < Rc prove to be among the best materials for use in batteries.
Micromagnetics of Critical Fields and Elementary Catastrophe Theory
Authors: Nieber S. , Kronmüller H.
Published: July 2007

Taking into account the anisotropy constants up to the sixth order the critical fields for the demagnetization mode of uniform rotation in uniaxial materials are derived. The boundary curves separating regions of material parameters with distinct critical behaviour are determined. The relation between uniform rotation and FOMP is discussed in the context of elementary catastrophe theory.
Magnetocaloric Measurements on Dysprosium Phosphate (DyPO4)
Authors: Hoffmann J.
Published: July 2007

DyPO4 orders below 3.39 K as a two‐sublattice Ising antiferromagnet with its moments along the crystallographic c‐axis. Measurements of the specific heat and the magnetocaloric effect with the magnetic field applied along c are performed to determine the phase diagram. A new intermediate ferrimagnetic phase is found at the metamagnetic transition from the antiferromagnetic to the paramagnetic state below 0.82 K. Although this phase extends only over a field range of about 20 mT, it is clearly seen since for crystals with finite demagnetising factor it produces additional mixed phases at the first‐order phase boundary. The measured phase diagram is verified by mean‐field calculations and the possibility of even more ferrimagnetic phases is discussed.
Contribution of Exciton Degenerate States to Multiphonon Resonant Raman Scattering
Authors: Riera R. , Sotolongo O. , Lang I. G.
Published: July 2007

A general method is given for the determination of multiphonon resonant Raman scattering (MPRRS) cross section when exciton degenerate states occur. The calculation is performed for exciton states with principal quantum number n = 2, when electron and hole effective masses are equal (me = mb). The results obtained can explain the special characteristics of secondary radiation emission spectrum in InBr and InI. It is shown that the MPRRS theory can be constructed on the basis of a classical approach, as for n = 1.
Molecular Dynamics Simulation of Vitrification and Plastic Deformation of a Two‐Dimensional Lennard‐Jones Mixture
Authors: Kotelyanskii M. J. , Mazo M. A. , Oleynik E. F. , Grivtsov A. G.
Published: July 2007

A computer model of a two‐dimensional atomic glass is generated by molecular dynamics. This model consists of 500 Lennard‐Jones particles of two different diameters. A volume‐temperature diagram is obtained. The bend found on this diagram at T = 0.28ϵ is interpreted as the glass transition. Density fluctuations and changes in the particles coordination numbers at the glass transition are studied by means of Voronoy polygons. The spatial correlation functions for particle displacements in the liquid and glassy states are analyzed. It is found that the glass structure is always a frozen liquid structure. Below the glass transition particle displacements from their equilibrium positions become spatially correlated, and the correlation length is greater than the model's size. Unusual roton‐like collective vibrational modes are found in the glass. The simulation of shear deformation shows that these modes may play an important role in the plastic deformation. No correlation is found between the diffusional mobility of particles and their local free volumes. This fact contradicts the main physical concept upon which a free volume approach is based.
Empirical N‐Body Interatomic Potential for B.C.C. Transition Metals
Authors: Ogorodnikov V. V. , Pokropivny V. V.
Published: July 2007

New thermodynamical expressions are derived for the energy and bulk module of the electron gas for cubic metals as functions of the electron Grüneisen parameter, specific electron heat capacity, coefficient of thermal expansion, Caushy discrepancy, and temperature. On this basis, interatomic potentials and a semi‐empirical equation for the volume dependence of a noncentral N‐body term are obtained. A formula is proposed for the temperature of the natural ductile‐brittle transition. The tendency established of this temperature to increase as the N‐body term decreases in the row Nb–Ta–V–Mo–W–Cr. The nature of the anomalous properties of Cr, the long‐range potential problem, and connection with other potentials are discussed.
The Quasiphonon Model of Amorphous Solids and the Percus‐Yevick Approximation
Authors: Kovalenko N. P. , Krasny Yu. P. , Weck G.
Published: July 2007

The quasiphonon model is used to describe thermodynamical features of amorphous solids in the low temperature range (T ≈ 20 to 50 K). Using the r‐representation of the particle interaction potential and correlation functions the quasiphonon dispersion relation ωα(k) of binary amorphous solids may be calculated analytically in the Percus‐Yevick approximation. This relation is obtained in a form with the characteristic roton‐similar minimum in the shortwave range of k. Even this minimum could be the reason for anomalous thermodynamical properties of such amorphous systems.
Impurity States in Quantum Wells Structures
Authors: Beril S. I. , Pokatilov E. P. , Zotov A. S. , Madkur S.
Published: July 2007

The shallow impurity center binding energy in a single quantum well is calculated by using the exact electron‐interaction potential. It is shown that the binding energy value corresponding to a simple model Coulomb potential \documentclass{article}\pagestyle{empty}\begin{document}$ V_{e - i} = - e^2 /\varepsilon _{eff} \sqrt {\varrho ^2} + (z_e - z_i)^2,\,\varepsilon _{eff} = \sqrt {\varepsilon _1 \varepsilon _2,} $\end{document} is less than the value, corresponding to the potential roughly by 15%, even for structure with very slightly different layer dielectric permittivities (a GaAs/AlxGa1‐xAs structure for example).
Ordered Superstructures of Oxygen Ions in La2MeO4+δ (Me = Cu, Ni)
Authors: Loktev V. M. , Tatarenko H. M.
Published: July 2007

Two‐dimensional commensurable ordered superstructures that can arise in La2MeO4+δ (Me = Cu, Ni) crystals are considered. It is shown that stable superstructures with δ = 0.125, 0.25, and 0.5 are formed as long‐range ordering of superstoichiometrical oxygen. The decomposition of a nonstoichiometric La2MeO4+δ compound into the ordered phases with stoichiometric compositions is proposed.
Lattice Dynamics of Formaldehyde
Authors: Weng S. X. , Anderson A.
Published: July 2007

A simple force constant model is described and applied to the vibrations of solid formaldehyde, H2CO and D2CO. Twenty adjustable parameters are used to obtain the best fit to the lattice mode frequencies and crystal field splittings observed by Raman and infrared spectroscopy. The use of symmetry coordinates to reduce the dimensions of the 96 by 96 original matrix is outlined. The dominant intermolecular interaction is confirmed to be that between carbonyl groups. The dependence of the force constants on interatomic separation is expressed in a simple exponential form.
Time‐Resolved Luminescence of Localized Excitons in CdS1—xSex under High Excitation
Authors: Urban M. , Schwab H. , Klingshirn C.
Published: July 2007

The temporal evolution of luminescence due to localized excitons in CdS1—xSex for various compositions from x = 0.02 to 0.55 is investigated after pulsed excitation (t ≈ 50 ps). The excitation intensity is varied from 8 × 105 W/cm2 up to 4 × 107 W/cm2. For the first time the luminescence dynamics is investigated under extremely high excitation into the extended states and it is found that the luminescence decay times, τD, become shorter and independent from the photon energy for high excitation. This behaviour is caused by the saturation of the localized states under high excitation. The x‐dependence of the “tailing parameter” and the total density of the localized states are discussed based on the experimental findings.
Temperature Dependence of the Dielectric Function of Orthorhombic GeS
Authors: Lukeš F.
Published: July 2007

The thermoreflectance spectra of orthorhombic GeS obtained in the 1 to 3.5 eV energy region as a function of temperature between 17 and 300 K for linearly polarized light with electric field vector E parallel to a‐ and b‐axes are used to determine the energies of the critical points Ei and broadening parameters Γi. The temperature dependence of the Ei values is analyzed in terms of average energies of phonons participating in the corresponding electron—phonon interactions. Also determined are the refractive index of GeS in the region of small absorption in the energy range of about 1 to 2 eV and its temperature dependence within the temperature interval 17 to 300 K from the interference effect.
Kinetics of A‐Luminescence in KCl:Tl Multiphonon Processes
Authors: Hlinka J. , Mihokova E. , Nikl M.
Published: July 2007

The decay kinetics of Tl+ UV‐emission in KCl: Tl is investigated in the wide temperature region 4.2 to 400 K. Two components — fast and slow ones are found. The results are interpreted with the help of a three level model with two excited states — radiative and metastable ones. Multiphonon nonradiative processes between these levels are involved to explain the temperature dependence of the fast component. Also the temperature dependence of transition probability between the metastable excited state and the ground state is included to improve the agreement between the experimental data and calculations.
Electronic Structure of a One‐Dimensional Superlattice
Authors: Lazo E.
Published: July 2007

By means of a one step matrix decimation and the transfer function method, the electronic structure of a one‐dimensional superlattice model is investigated. All the Green function components corresponding to the basic cell that form the superlattice are obtained inverting a unique complex matrix of coefficients. The method permits to calculate the local properties on each site of the basic cell. The global density of states obtained is compared with the results given by the negative‐eigenvalue theory of Dean.
Practicable Method for Estimating Thermal Depths from Phonon‐Broadened Photoexcitation Cross‐Section Bands I. Foundations
Authors: Pässler R.
Published: July 2007

Photoexcitation cross‐sections of deep traps in semiconductors that are thermally broadened by multiphonon (MP) emission and absorption are represented by convolutions of electronic parts with thermally averaged Franck‐Condon factors. A trap‐independent MP absorption versus emission probability relation following from analytical expressions for the limiting case of vanishing phonon dispersion is generalized to arbitrary dispersion of phonon energies assumed, however, to remain unchanged during a transition. Corresponding Franck‐Condon factors are shown to decompose into products of a universal exponential factor, exp (−ΔE/2kT), and system‐specific parts representing symmetric functions of the vibrational energy difference ΔE. On this basis an upper bound is derived for the ground‐to‐first‐excited level distance from the vertex position of the correspondingly transformed photoexcitation cross‐section band. The exemplification for the case of electron excitation from the oxygen donor level (state 1) in gallium arsenide shows reasonable agreement with results obtained by other methods.
Carrier Drag in Modulation Doped Quantum Wells
Authors: Gerlach E. , Kaser A.
Published: July 2007

A fluctuation concept is applied to describe the ‘negative absolute mobility’ of minority carriers in ‘modulation doped quantum wells’ found experimentally by Höpfel et al. The observed linear and nonlinear effects arise from a competition of carrier–carrier and carrier–phonon and carrier–ion scattering.
An Estimate of the Dependence of the Ising Critical Exponents on the Lattice Dimensionality
Authors: Silva P. R.
Published: July 2007

Upper and lower bounds are estimated of the two‐point correlation function exponent, η, of the Ising model, as a function of the lattice dimensionality, d. The average value of these two bounds together with the correlation length critical exponent v(d) evaluated by Thompson, lead to a set of critical indexes which satisfy the hyperscaling relation. This set of exponents also shows an adequate agreement with the results obtained by Le‐Guillou and Zinn‐Justin for the Ising model in non‐integer dimensions, in a large range of the parameter d.
Sublattice Structure of a Site Dilute Ising Lattice
Authors: Sikakana I. Q. , Lowther J. E.
Published: July 2007

The distribution of spins on a quenched two‐dimensional Ising lattice is examined using Monte Carlo techniques and related to the critical properties. A sublattice structure is defined, and the spin distribution on each sublattice investigated as dilution and temperature change.
The Shape of a Spectral Hole and Its Temporal Response at Short Burning Times in Two‐, Three,‐ and Four‐Level Systems
Authors: Rebane I. K.
Published: July 2007

The shape of the spectral hole in an inhomogeneous distribution function of centres over the transition frequency is calculated for the case of a quasimonochromatic burning light pulse which characteristic duration time is comparable to the relaxation times of the excited electronic level. Two‐step spectral hole‐burning in the cases of three‐ and four‐level systems as well as one‐step processes are considered. The temporal responses of the spectral holes as spectral filters on δ‐pulse of light are found.
Galvanomagnetic Luminescence Spectra of InSb
Authors: Kessler F. R. , Paul R. , Nies R.
Published: July 2007

In crossed electric and magnetic fields inside an intrinsic semiconductor a free carrier compression takes place due to the Lorentz force (LF). This leads to a free carrier profile containing regions of enhancement as well as of depletion of free electron–hole pairs. These deviations from the equilibrium concentration lead to a “galvanomagnetic luminescence (GL)” which is positive or negative in relation to the equilibrium temperature radiation. The measured GL spectra of InSb show a double peak at about 5.6 μm wavelength due to g‐factor splitting of the Landau level involved. The evaluation of the GL spectra (as function of magnetic field up to 14 T) by means of model calculations leads to the determination of the energy dependent band parameters: effective mass and Landé factor corresponding to the strong nonparabolicity of the conduction band of InSb. The integral radiation output of GL is also measured as function of the LF showing an increase of the quantum efficiency of emission of radiation due to (i) a saturation effect of the surface recombination velocity and (ii) a reduced diffusion length at increasing magnetic field leading to a corresponding profile enhancement.
Relationship of Triple Point Solid Volume with Thermo‐Acoustic Parameters and Structural Distortion in Quasi‐Spherical Molecular Liquids by the Corresponding State Correlations
Authors: Sharma B. K.
Published: July 2007

The significance and the validity of the idea of corresponding state correlations is tested by obtaining unique values for reduced triple point solid volume, Boyle temperature, critical state nearest‐neighbour number, and intermolecular separation, using critical volume and temperature as reduction parameters. The calculated values show very close agreement with experimental values for simple, non‐polar, spherical liquids. An attempt is made to obtain an expression for liquid structure distortion parameter in terms of the reduced molar volume of the liquid. It is shown that the effect of distortion parameter on structural variations with regard to change in nearest‐neighbour number with temperature in liquid argon is significant. The results are used to develop a relationship between the thermo‐acoustic parameters on the basis of liquid structure distortion and the hard‐sphere model with attractive interactions in simple liquids.
On the Intrinsic Ductility and Brittleness of Crystals
Authors: Pokluda J. , Šandera P.
Published: July 2007

Intrinsic ductile versus brittle response of ideal crystals containing cracks is theoretically analyzed using a modified Kelly‐Tyson‐Cottrell approach. A new criterion based on the three‐axial ideal tensile strength and the normal‐stress dependence of ideal shear stress is proposed. A great variety of possible crack/slip configurations is evaluated by means of computer in order to estimate the intrinsic response of f.c.c., b.c.c., h.c.p., and diamond crystals. The result of this crystal‐calibration is, in general, in a good agreement with available experimental data.
An Investigation of Smectic A—Nematic and Nematic—Isotropic Phase Transitions
Authors: Alapati P. R. , Saran D.
Published: July 2007

The phases and phase transitions in two homologues of the 4‐(4′‐n‐alkyloxy‐benzoyloxy) benzylidene‐2″‐methylaniline (decyloxy and dodecyloxy) are characterized using a variety of experimental techniques. These are differential scanning calorimetry, thermal microscopy, X‐ray diffraction, ESR spectroscopy, and density determination. The nematic—isotropic transition is found to be of first order but with a smaller transition entropy, in both of the compounds, than expected. The smectic A—nematic transition is found to be of weak first order in both of the compounds. The experimental results are compared to those of other compounds which have comparable molecular lengths and with the predictions of a molecular field theory of smectic A liquid crystals.
On a Dislocation Core Tensor
Authors: Maruszewski B.
Published: July 2007

An attempt is made that may lead to a new definition of the dislocation density field. The idea is based on the fact that dislocation cores form a kind of network of infinitesimally thin pores or capillary tubes in the crystal lattice. The main aim of the new description of the dislocation density field is focused on a way which differs from the definition based on a local distortion field coming from lattice line defects.
Theorie du ferromagnétisme itinérant dans des semimétaux supraconducteurs
Authors: Tran C. Do , Manh D. Nguyen , Van C. Nguyen
Published: July 2007

Une théorie du ferromagnétisme itinérant dans des semimétaux supraconducteurs est proposée. Une aimantation moyenne apparait dans l'état supraconducteur due à l'interaction (interférence) des ondes: onde de densité de spin, onde de densité de charge et onde des paires de Cooper. Le diagramme des phases et les propriétés physiques des états examinés sont étudiés analytiquement et numériquement.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals IV. Isomorphous Substitutions. Raman Spectra of [(CH3)2NH2]2ZnCl4 and [(CH3)2NH2]2CoCl4 Crystals
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I. , Bobrova Z. A.
Published: July 2007

The polarized Raman spectra of recently synthesized [N(CH3)4]2ZnCl4 and [(CH3)2NH2]2CoCl4 crystals are obtained. The structure of these spectra exhibits strong similarities with that of [N(CH3)4]2ZnCl4. The vibration spectra of these crystals at room temperature are analyzed and the similarity of the spectra with those of the ordered low‐symmetry phase (176–155 K) of the [N(CH3)4]2ZnCl4 crystal is discussed.
Excitonic Excitation of Cu Luminescence in ZnSCu, Cl Crystals
Authors: Brandt S. , Jaszczyn‐Kopec P.
Published: July 2007

An excitation peak is observed at Ax energy (A = intrinsic exciton) for the Cu blue (CuB), and at AxLO for the Cu green (CuG) luminescence in a ZnSCu, Cl cubic crystal. It is shown that the difference in the two peaks position is due to the localization of CuB luminescence centers at the surface and that of the CuG in the bulk of the crystal. The excitonic excitation of the blue emission is attributed to the Auger process decay of the excitons bound to the (CuZnCui) complex. The possibility of exciting the CuGDA pairs, not only via binding the excitons, but also by the energy transfer from the excitons bound to other impurities, is considered.
Fluorescence and Upconversion in CaF2:Ho3+
Authors: Tang S. H. , Zhang H. Y. , Kuok M. H. , Kee S. C.
Published: July 2007

Laser excitation studies of CaF2 crystals doped with 0.01 to 10% Ho3+ using the second harmonic wavelength 532 nm of a pulsed Nd: YAG laser are carried out. Three fluorescence bands belonging to the 5F4, 5S2 → 5I8, 5F4, 5S2 → 5I7 and 5F5 → 5I8 transitions are detected. Fluorescence lifetimes of the first two transitions are measured and used for site‐identification of new lines. Four upconverted fluorescence bands belonging to the 5F3 → 5I8, 5G4 → 5I8, 5G5 → 5I8, 5H5, 5H6 → 5I8 transitions are also detected. A comparative study is made of two pairs of energy transfer mechanisms, which are multiphonon relaxation versus ion‐pair relaxation and two‐photon absorption versus ion‐pair relaxation. The analysis of the concentration dependence of fluorescence intensities shows that ion‐pair relaxation is the chief mechanism responsible for the fluorescence and upconversion behaviour of CaF2:Ho3+.
Formation and Decay of Electronic Excitations Localized near Divacancies in Alkali Halides
Authors: Lushchik A. , Lushchik Ch. , Lushchik N. , Frorip A. , Nikiforova O.
Published: July 2007

The thermal quenching or plastic strain of RbCl, KCl, and KBr crystals leads to an increase in the number of associations of anion and cation vacancies. Using the methods of VUV spectroscopy, electronic excitations localized near divacancies are detected at 5 K. The process of radiative and nonradiative decay of these excitations is studied as well as the process of radiational creation of divacancies.
The Condensation and Ferromagnetism of Triplet Frenkel Excitons
Authors: Li Bao‐Xing
Published: July 2007

The problem of coexistence of condensation and ferromagnetism in the triplet excitonic system is studied by using the symmetry‐broken Hartree approximation. It is found that the ground state of the system is the mixed state of both orders. Two kinds of particular cases, pure condensing phase and pure ferromagnetic phase, are discussed. A phase diagram is obtained from the calculation of free energies.
Fermi Surface Properties of Platinum
Authors: Ahuja R. , Solanki A. K. , Auluck S.
Published: July 2007

The extremal areas of the Fermi surface of paramagnetic f.c.c. transition metal platinum are calculated using the linear muffin tin orbital (LMTO) method in the atomic sphere approximation. To see the effect of exchange and correlation potential on the Fermi surface, the calculations are done using various exchange and correlation potentials. The Slater Xα exchange potential with α = 0.815 gives the best agreement with experimental data. Inclusion of relativistic effects also show remarkable improvement over the non‐relativistic calculations for platinum. The Fermi velocity of electrons at the Fermi surface and the mass enhancement factor are also calculated using the Slater Xα (α = 0.815) exchange potential and are compared with the experimental data and recent theoretical calculations.
Collective Behaviour of Photoinjected Plasma in Semiconductors
Authors: Esperidião A. S. , Vasconcellos A. R. , Luzzi R.
Published: July 2007

The spectrum of elementary excitations in the nonequilibrium state of a semiconductor under high levels of continuous photoexcitation is studied. Resorting to a quantum transport theory based on the nonequilibrium statistical operator method, the dynamic dielectric response function of the carrier system in the far‐from‐equilibrium steady state is derived, to calculate the Raman scattering spectrum and from it to analyze the spectrum of elementary excitations. Besides the expected bands due to quasi‐particle and collective plasma excitations, the presence is demonstrated of two additional bands associated to low energy excitations and with a linear dispersion relation, and hence termed acoustic plasma modes. The analysis of these two bands points to an interpretation of them as due to the collective motion of the electrons (the ones higher in energy) and of the holes (the ones lower in energy) interacting through the screened Coulomb interaction. At low temperature their lifetimes are mainly determined by dissipative effects mediated by the interaction of the carriers with the radiation recombination field.
Characteristics of Permanent Magnetic Coercivity with Application to Sintered Hard Ferrites
Authors: Elk K. , Jahn L.
Published: July 2007

To get information on the magnetization processes of permanent magnetic materials the angular dependences of the coercivity Hc, the remanence coercivity HR, and the maximum position H of the total susceptibility are investigated. Considering two competing coercivity mechanisms and two different magnetic prehistories the differences between these three quantities are demonstrated by model calculations and experimental results on hard ferrites. It is shown that HR(θ) is the most suitable measure to describe the irreversible magnetization processes in polycrystalline hard magnets.
The Re‐Entrant Behaviour of the Spin‐One Ising Model
Authors: Kerouad M. , Saber M.
Published: July 2007

A spin‐one Ising model with random nearest‐neighbour interactions is studied within the finite cluster approximation (FCA). The application is discussed of FCA to the spin‐one Ising model with random nearest‐neighbour exchange interactions on a honeycomb lattice according to a two‐valued distribution of the random interactions. Re‐entrant phase diagrams are found.
Resonant Cavities for X‐Rays. Dynamical Diffraction of Dipole Radiation at Bragg Angles near π/2
Authors: Caticha A. , Caticha N.
Published: July 2007

The X‐ray field radiated by a classical oscillating point dipole inside a crystal is calculated in a non perturbative way. In the interesting situation in which Bragg's angle is near to π/2 it is shown that the crystal acts as a resonant cavity.
Cohesive and Anharmonic Properties of Some Fluorite Structure Nitrates
Authors: Rao C. N. , Singh R. K. , Hasan S.
Published: July 2007

A three‐body potential (TBP) model is used to describe the cohesive and anharmonic properties of strontium, barium, and lead nitrates of fluorite structure. This TBP model consists of the long‐range Coulomb and three‐body interactions and the short‐range van der Waals attraction and overlap repulsion effective up to the second neighbour ions. This model reveals a better description of the cohesion, third‐, and fourth‐order elastic constants, and pressure derivatives of the second‐order elastic constants of these nitrates than those obtained by earlier workers. The scope for improvements is also discussed.
Influence of Short‐Range Order on the Electron–Phonon Interaction in Disordered Binary Alloys
Authors: Gurskii Z. A. , Chushak Ya. G.
Published: July 2007

A microscopic theory for the investigation of the short‐range order effects on electron–phonon interaction in binary alloys is proposed. An expression for the electron–phonon matrix element is derived. Due to the presence of disorder in alloys, an additional term arises in this matrix element in comparison to the case of pure metal. The influence of pair correlations on the Eliashberg function α2F(ω) and the electron–phonon interaction constant in alloys of the KRb and KCs systems is investigated numerically and is analyzed. The pair correlations are shown to cause an increase of the electron–phonon interaction constant in the vicinity of the phase instability point. Under certain conditions such an increase may be essential.
Thermodynamic Investigations of the Phase Transition in Ferroelastic CoZrF6
Authors: Gorev M. V. , Flerov I. N. , Tressaud A. , Grannec J. , Rodriguez V. , Couzi M.
Published: July 2007

The heat capacity and the pressure dependence of the phase transition temperature of CoZrF6 are measured. The first order phase transition Fm3m → R3 is characterized by large values of both, the entropy change ΔS = (5.8 ± 0.8) J mol−1 K−1 and the rate of increase of the transition temperature T0 with applied hydrostatic pressure, dT0/dp = (340 ± 40) K GPa−1. An analysis of the results is performed in terms of the Landau theory. The parameters of the thermodynamic potential are determined.
E(k) above the Vacuum Level from Low Energy Electron Reflection. ΓK Line of Cu and Ni
Authors: Strokov V. N.
Published: July 2007

Incidence angle dependent electron reflection coefficient curves R(E) measured in the 0 to 30 eV range on Cu(111) and Ni(111) surfaces are analysed. With incidence scanning in ΓK azimuth, some extrema of the dR/dE curves are shown to manifest bands along the ΓK line of the Brillouin zone. Comparing the experimental angular dispersion of these extrema with its calculated counterpart, bands along ΓK are mapped. Experimental technique and details of calculation are briefly discussed.
Influence of Intercalation by Metallic Atoms on the Shubnikov ‐de Haas Effect and the Energy Spectrum of Bi2Te3
Authors: Kulbachinskii V. A. , Kovalyuk Z. D. , Pyrlya M. N.
Published: July 2007

Li and Ba atoms are intercalated into the van der Waals gaps of Bi2Te3 single crystals of n‐ and p‐types. The resistivity, the Hall effect, and the Shubnikov‐de Haas effect are investigated in host single crystals and after intercalation. It is found that the scattering of carriers is connected preferentially with acoustic phonons and does not change after intercalation. The intercalation of metallic atoms causes a change in the carrier concentration and hence, the Fermi energy. The intercalated samples possess the same six‐ellipsoidal Fermi surface as the host material.
Spin Waves in a Generalized Anderson‐Lattice Model
Authors: Irkhin V. Yu. , Entelis A. M.
Published: July 2007

A two‐band model is considered describing, in particular, intermediate‐valence and Kondo systems and high‐Tc superconductors. Spin‐wave and electron spectra in ferro‐ and antiferromagnetic states are calculated both within the generalized Hartree‐Fock approximation and in the limit of strong correlations (with the use of perturbation theory in the fluctuating part of hybridization).
Calculation of the Spin System Correlation Functions in the Frames of the Functional Integration Methol. I. The Ising Model
Authors: Vakarchuk I. A. , Matskevych P. A.
Published: July 2007

The equations for the spin system correlation functions and Green functions as well as the way of their self‐consistent solution are suggested in the frames of functional integration method. As an example the Ising model is considered. The Curie temperature of this model is calculated from the pole of the pair correlation function. Calculations are performed for the cases of the crystalline and amorphous system. The value of critical temperature in the crystalline case is in good agreement with known data. It is shown that the magnetic order can be destructed by amorphization of the crystal.
EXAFS Study of the CuAsSe Amorphous Alloys
Authors: Gómez‐Vela D. , Esquivias L. , Prieto C.
Published: July 2007

Some amorphous alloys of the chalcogenide CuAsSe family are studied by EXAFS spectroscopy. Results are presented, obtained for the two samples Cu8As26Se66 and Cu26As37Se37. The mean coordination number of the three different atoms and their distances to the first coordination sphere are determined in both the alloys. It is found that the copper atoms are fourfold and the arsenic ones are threefold coordinated in both the compounds and the coordination numbers for selenium are 3.8 and 2.2 in Cu8As26Se66 and Cu26As37Se37, respectively.
Setting‐up of a Generalized Clustering Model in Fluorite‐Type Anion Excess Solid Solutions
Authors: Réau J. M. , Wahbi M. , Sénégas J. , Hagenmuller P.
Published: July 2007

A model correlating ionic conductivity to short‐range order in fluorite‐type anion excess solid solutions is proposed. It is based on the composition dependence of the number of the fluoride ions appearing to account for the long‐range motions. The validity of this generalized clustering process model is checked by 19F NMR and/or neutron diffraction investigations.
Reference System Approach in the Electron Liquid Theory. II. Ground State Characteristics in the Medium Density Region
Authors: Vavrukh M. , Krokhmalskii T.
Published: July 2007

It is shown that the reference system approach (see part I of this paper), based on the application of n‐particle correlation functions of a degenerate system of noninteracting electrons, proves to be efficient in describing the interacting electron gas in the medium density region. The energetic, dielectric, and structural characteristics of the homogeneous electron liquid ground state are obtained as functions of the coupling parameter rs.
Bulk Photovoltaic Effect in LiTaO3: Fe Crystals
Authors: Karabekian S. I. , Odoulov S. G.
Published: July 2007

Four independent components of photovoltaic tensor, responsible for “linear” photovoltaic currents, are measured for the first time for LiTaO3: Fe crystals in the range of photon energy from 2.07 to 3.88 eV. The observed correlation of the spectral dependencies of βs15 and β22 components indicates common origin of the transverse linear photovoltaic currents in this material.
Interplane Cooper Pairing in YBa2Cu3O7 Crystals and Phonon Frequency Softening Below Tc as a Consequence of Electron‐Phonon Interaction
Authors: Liaptsev A. V.
Published: July 2007

A model of the YBaCuO crystal based on tight‐binding approximation is considered. The electronic Hamiltonian describes uncoupled plane (layer) bands and chain bands. The vibronic interaction appears due to the overlap of Cu2(d) and O4(pz) orbitals when the nuclei are displaced from their equilibrium positions. This interaction is transformed to the Renner‐type vibronic interaction which is nondiagonal with respect to the indices corresponding to different planes and quadratic in the vibronic coordinates. It is shown that the Renner‐type interaction can cause interplane pairing of electrons and phonon frequency softening below Tc. Some estimates are obtained and compared with experimental data.