bluuebunny/crossref_metadata_2025_split huggingface dataset:
Discovery of low‐temperature metastable state in amorphous bismuth—hydrogen systems
Authors: Belevtsev B. I. , Komnik Yu. F. , Odnokozov V. I. , Fomin A. V. 
Published: July 2007

AbstractElectric and superconducting properties of Bi films condensed in the H2 atmosphere (pH2 = = 5 × 10−6 to 2 × 10−5 Torr) onto a liquid‐helium‐cooled substrate are studied. The dissolved hydrogen is found to increase essentially the resistivity Q, to suppress Tc and raise the amorphous—crystalline transition temperature Tac. If pH2 exceeds some critical values, the films prepared are in the metastable phase, a‐Bi(H), highly saturated with hydrogen. At about 5 K this phase transforms into ordinary, also metastable, amorphous Bi, which results in a sharp decrease of the normal resistance (down to two orders of magnitude) and a Tc rise (up to 2 K). In a number of cases this transition proceeds as a heating‐induced jump from the resistive to the superconducting state. The properties of pure and hydrogen‐saturated Bi films are thoroughly compared. The results obtained are discussed on the base of the up‐to‐date knowledge.
A new theoretical approach to the low‐temperature specific heat of disordered solids
Authors: Hüttner B. , Pompe W. 
Published: July 2007

AbstractStarting from a perturbation theory for the free energy of disordered solids, the anomalous temperature dependence of the specific heat can be calculated. The model under consideration is based on the two common features of a large group of disordered solids, firstly, the distorted SRO, and, secondly, the cluster‐like arrangement of strongly distorted atoms which are imbedded in a crystallike matrix. The theory yields the increase of the specific heat proportional to T for very low temperatures and the anomalous high value of the T3‐term. The calculated values coincide very well with the experimentally determined temperature dependence for disordered covalent solids.
Variable reconstruction of dislocation cores in Si
Authors: Mergel D. , Labusch R. 
Published: July 2007

AbstractPhotoconductivity spectra and Hall‐effect measurements of deformed Si samples with different doping concentrations and dislocation densities suggest a dependence of the dislocation energy levels on their occupation. This is in contrast to the widely used rigid‐band‐model. A Peierls‐like structural transition in the core of a 90°‐partial is discussed as the most likely explanation of this effect.
Electron spin resonance of doped glow‐discharge amorphous germanium
Authors: Stutzmann M. , Stuke J. , Dersch H. 
Published: July 2007

AbstractESR‐spectra and transport properties of a‐Ge:H, prepared by decomposition of GeH4 in a glow‐discharge, are investigated for different phosphorus and boron doping. Undoped and moderately doped samples show the usual resonance at g = 2.0225 due to dangling bonds. For high doping levels, however, two new lines are found: high boron doping leads to a resonance at g = 2.0535 with a linewidth of 112 G, high phosphorus doping to a line at g = 2.0120 with ΔHpp = 33 G. These lines are attributed to localized holes and electrons in the tails of valence and conduction band, respectively. The linewidth of all resonances is the combination of a g‐spectrum ΔHpp(g) and a considerably smaller residual linewidth ΔHpp(r) caused by unresolved hyperfine interaction. A simple relation between the g‐shift g–g0 and ΔHpp(g) is found which explains the similar doping dependence of g‐value and linewidth. From the dependence of the spin density Ns on the conductivity activation energy Eσ a model for the density of states in the mobility gap is deduced. A comparison between the ESR‐data of a‐Ge: H and a‐Si: H shows that g‐shifts and linewidths of the three resonances are for a‐Ge: H by a factor of about six larger than for the corresponding lines of a‐Si: H.
Infrared absorption spectra of Cd0.2Hg0.8Te crystals
Authors: Gurauskas E. , Kavaliauskas J. , Krivaite G. , Šileika A. 
Published: July 2007

AbstractThe investigations of infrared absorption spectra of Cd0.2Hg0.8Te crystals containing inclusions of tellurium surrounded by semimetal phase are carried out in the spectral region 10 to 40 μm at 120 and 300 K. An increase of absorption coefficient and a change of its spectral dependence due to the inclusions are found. Numerical calculations are made of free‐carrier absorption spectra taking into account scattering by acoustic phonons, optical phonons, and ionized impurities. In addition, the extinction spectra due to the absorption and scattering of light by Te and HgTe particles in Cd0.2Hg0.8Te crystals are calculated, too. It is shown, that infrared absorption spectra of Cd0.2Hg0.8Te can be explained by free‐carrier absorption including the extinction of light by inclusions of a semimetal phase (HgTe).
Recherches théoriques sur l'autodiffusion dans les cristaux ioniques
Authors: Guerin P. , Laforgue A. 
Published: July 2007

AbstractNous présentons une méthode, déduite de la théorie de la vitesse absolue de réaction, pour étudier la migration du cation dans les cristaux d'halogénures alcalins. Cette méthode est appliquée dans le cadre de trois approximations décrivant les propriétés des ions. La première approximation nous permet de tracer des lignes équipotentielles dans des sections planes de la surface de potentiel. Contrairement à l'idée admise, la voie de diffusion n'est pas rectiligne; en effet on met en évidence deux voies de diffusion planes. Ce résultat est confirmé avec NaCl, dans le cadre de notre troisiàme approximation (la plus fine). Ces deux voies sont alors séparées par une barriére de potentiel de 0,01 eV, les énergies de Schottky et de migration sont respectivement égales à 2,03 et 0,69 eV.
Some optical and electrical measurements on Cs3Bi2Br9 single crystals
Authors: Timmermans C. W. M. , Cholakh S. O. , van der Woude R. L. , Blasse G. 
Published: July 2007

AbstractThe optical properties of Cs3Bi2Br9 in the spectral range 2 to 10 eV are reported and discussed. The results are interpreted with the aid of the calculated band scheme of CsPbBr3. The band edge is situated at 2.707 eV and is ascribed to a transition from the bismuth (6s) valence band to the bismuth (6p) conduction band. The intracationic exciton transition, which takes place at 2.699 eV, is allowed but with a low transition probability. Photoconductivity measurements reveal that the electrons are the more mobile charge carriers.
Electroconduction and thermoelectricity of terbium oxide films
Authors: Smolin M. D. , Andreeva A. F. , Ogorodnik V. A. 
Published: July 2007

AbstractThe dependence of electric conductivity and thermoelectric power of terbium oxide films TbO1.75−x upon the temperature (250 to 600 °C) and oxide composition (x = 0 to 0.25) is investigated. The results obtained are interpreted in terms of the small polaron theory. The thermoelectric power of TbO1.75 does not depend on temperature and is equal to −35 μV/K and the dependence of thermoelectric power of TbO1.75−x on the parameter x is in accordance with Heike's formula for the hopping. Also, some parameters of charge transfer mechanism motion are determined. The activation energy of drift mobility of small polarons in TbO1.75 is equal to 0.40 eV and the small polaron radius is equal to 0.21 nm. The concentration of small polarons in TbO1.75−x does not depend on temperature and is equal to the concentration of trivalent terbium ions.
Soliton excitations in one‐dimensional molecular systems
Authors: Brizhik L. S. , Davydov A. S. 
Published: July 2007

AbstractIt is shown that the presence or the absence of a soliton excitation threshold and the threshold values depend on the character of the excitation distribution at the initial time moment. A study is made of the time evolution of an excitation given at the initial moment as a hyperbolic secant, in form of a rectangular step, and as a decreasing exponential.
Thermal conductivity of germanium containing dislocations at low temperatures
Authors: Ansari M. A. , Kumar Anil , Srivastava B. K. 
Published: July 2007

AbstractTo study the frequency dependence of the phonon–dislocation scattering, the phonon conductivity of germanium with dislocations is analysed using Holland's model and Kumar and Sinha's relaxation time for the phonon–dislocation scattering processes. A reasonably good agreement is observed between present theory and experimental data of Sato and Sumino.
A binary ferromagnetic alloy with magnetic moments dependent on local environment. II. Neutron magnetic elastic scattering and hyperfine field distribution
Authors: Zaborov A. V. , Medvedev M. V. 
Published: July 2007

AbstractThe neutron magnetic elastic scattering and the hyperfine field distribution are calculated for a collinear ferromagnetic alloy with magnetic moments which depend on their local chemical environment in a step‐like manner (Jaccarino‐Walker model). The question is analyzed how, using experimental data, one can discern the model under study from a binary magnetic alloy with competitive nearest‐neighbour exchange interactions and permanent magnetic moments. In the framework of the Jaccarino‐Walker model the concentration dependences of the spontaneous magnetization and Curie temperatures for Ni and Co alloys with elements of the Pt as well as Pd group are considered.
Molecular‐type channeling of relativistic electrons in crystals
Authors: Vyatkin E. G. , Filimonov Yu. M. , Taratin A. M. , Vorobiev S. A. 
Published: July 2007

AbstractChanneling of relativistic electrons in 〈110〉 direction in a diamond crystal and the channeling radiation spectra are investigated using computer simulation by the binary collision model and using the model of a continuum potential of the atomic rows. In a computer experiment the atomic‐ and molecular‐type states of channeled electrons are revealed, and the orientational dependence of the electron trapping probability in these states is obtained. The peculiarities revealed of the angular distributions and radiation spectra of electrons in the molecular‐type states allow to discover these states in the experiment.
Reflectance and thermoreflectance spectra and energy band structure of GeSe crystals
Authors: Valiukonis G. , Gashimzade F. M. , Guseinova D. A. , Krivaitė G. , Kulibekov A. M. , Orudzhev G. S. , Šileika A. 
Published: July 2007

AbstractThe reflectance spectra of orthorhombic GeSe crystals are studied in the region 0.5 to 12 eV in polarized light with E ∥ a and E ∥ b at 290 K and a Kramers‐Kronig analysis is performed. The thermoreflectance spectra are investigated in the region 1 to 5 eV for E ∥ a and E ∥ b at 300 and 90 K. The energy band structure calculations of GeSe are carried out by the pseudopotential method, and the spectra of the imaginary part of the dielectric constant are calculated by the k · p method. A classification and interpretation of main structures of optical spectra of GeSe by direct interband transitions at critical points T, U, T and high symmetry lines B' V, A is presented on the basis of calculated band structure and selection rules for optical dipole transitions of orthorhombic A4B6 crystals.
Influence of directed chemical bonding on the structure of metallic glasses
Authors: Hermann H. 
Published: July 2007

AbstractNon‐central potentials are used to describe directed chemical bonding due to metalloids in amorphous metal—metalloid systems. Average atomic volume, partial pair distribution functions, local symmetries, and correlation functions of symmetry coefficients are calculated for two‐dimensional model systems produced numerically by simultaneously carrying out density variation and energy relaxation. The model reproduces qualitatively essential experimental results.
A theoretical investigation of the fermi surfaces of bismuth and antimony
Authors: Rose J. , Schuchardt R. 
Published: July 2007

AbstractThe band structure and Fermi surfaces of Bi and Sb are studied with four different semiempirical pseudopotentials. By application of a Golin potential screened by the Heine‐Abarenkov form of dielectric function reasonable band structures are obtained. The calculated Fermi surfaces show very good agreement with the experimental data. Remaining discrepancies with respect to lower lying valence bands are analysed and compared with other calculations.
Decay behaviour of high‐excitation luminescence in Gap:N II. Experimental results on the densities of the coexisting phases and the relevant recombination processes
Authors: Weinert H. , Bindemann R. , Kreher K. 
Published: July 2007

AbstractThe radiative recombination of isoelectronic nitrogen‐doped GaP is investigated under high optical excitation at several temperatures (T = 2, 4.2, 27, and 77 K). A previously reported phase seperation is confirmed. The parameters of the electron—hole liquid and the coexisting low‐density phase are determined both from luminescence spectra and decay measurements. The dominating recombination processes for the carrier system are found to be phonon‐assisted band‐to‐band Auger recombination, phononless radiative recombination with participation of the nitrogen impurities, and phononless Auger recombination with participation of the nitrogen impurities. The respective rate coefficients are determined.
Electron localization on defects and optical nuclear polarization in disordered and semimagnetic semiconductors
Authors: Bagraev N. T. 
Published: July 2007

AbstractUsing optical nuclear polarization (ONP) and nuclear magnetic resonance (NMR) techniques silicon single crystal solid solutions containing impurity defects of more than one kind are studied. The application of the ONP techniques to the investigation of nonuniformly doped silicon is demonstrated. The concentration and energy fluctuations of donor levels are determined in silicon doped with elements of III to V and transition groups. Solid solution decay processes are studied by ONP techniques in silicon crystals doped with deep‐level impurities. Finally, the ONP technique is applied to the investigations of semimagnetic semiconductors.
Study of the Single and Double Groups CS and SS and Properties of Their Two Isomorphisms
Authors: Le Paillier‐Malecot A. 
Published: July 2007

AbstractThe C8 group is isomorphic to the S8 group, so with the inversion isomorphism for these double groups, the character table, the multiplication table, and the full rotation group compatibility table are established. Another isomorphism, Tisza's isomorphism, is defined. The study of the properties in the two isomorphisms shows the main advantages of the inversion isomorphism. Finally for groups having the Sn operation (n = 5, 8, 10 and 12) the correspondence between improper and inverse rotations is given and for a doubly degenerate species (with J = 1) the character value is calculated which is irrational.
Impurity Band Conduction in HgTe I. Experimental Data
Authors: Dziuba Z. 
Published: July 2007

AbstractThe magnetic field dependence of the electrical conduction in HgTe samples at 4.2 K is analysed taking into account the energy dependence of the carrier mobility. The concentration and mobility of the electric carriers are calculated. The electrical conductivity in HgTe samples at low temperatures is described by electrons in the conduction band, holes in the valence band, and electric carriers in an impurity band. The electric carriers in the impurity band behave in the magnetic field like electrons and holes with comparable values of mobility and concentration. The electrical conductivity shows a strong dependence of the mobility on the energy of the conduction band electrons.
On the Configuration Coordinate Diagram of ZnS:Fe
Authors: Zimmermann H. , Boyn R. 
Published: July 2007

AbstractA discussion is given of the configuration coordinate diagram of ZnS:Fe, which is partly based on experimental data obtained by the authors in this and in a preceding paper. Intraimpurity transitions in Fe2+ → Fe3 + e (I) and Fe3+ → Fe2+ + + h (N) are included. For the latter transitions the zero‐phonon threshold energies are found to be 2.45 eV and 1.38 eV, respectively, at 80 K, and a value of 0.375 eV is obtained for the lattice‐ relaxation energies. In the absorption spectrum at 2 K sharp lines are observed above the zerophonon threshold energy of transition I, and these are attributed to 3d‐levels in resonance with the conduction band.
Scattering of Axially Channeled Particles by Atomic Strings in Crystals
Authors: Cherdyntsev V. V. , Pokhil G. P. , Ryabov V. A. 
Published: July 2007

AbstractThe motion of axially channeled particles at shallow depth is analytically treated. It is shown that there may exist finite trajectories for particles with energies of the order of the critical energy. The effect of focusing upon backscattering yield oscillations is examined. For the transition from axial channeling to planar one, the self‐consistent solution of the equations of motion is obtained, which allows to take an exact account of the discrete arrangement of atomic rows making up a planar channel. An analysis of this solution offers a new interpretation of the processes occurring at such transitions.
Carrier Statistics in Superlattices of Small‐Gap Semiconductors in the Presence of a Quantizing Magnetic Field
Authors: Ghatak K. P. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to formulate the generalized carrier statistics in superlattice structures of small‐gap semiconductors by deriving expressions for the density‐of‐states function and the carrier concentration in such structures in the presence of a quantizing magnetic field. The corresponding expressions for superlattices of large‐gap semiconductors can easily be obtained from the generalized relations derived. These results would be more general than those reported in the literature for such structures of large‐gap semiconductors on the basis of tight‐binding approximations.
Anharmonic Study on the Debye‐Waller Factor for a Vacancy‐Trapped Mössbauer Impurity in Solid Solution of Aluminium
Authors: Acharyya P. K. , Tewari A. K. , Roy S. K. , Bhattacharya D. L. 
Published: July 2007

AbstractThe effect of anharmonicity on the Debye‐Waller factor for a simple cubic lattice containing Mössbauer atoms as impurity along with vacancies at the lattice points is evaluated theoretically using the double‐time Green's function technique in the high‐temperature limit. The contributions of the anharmonic lattice vibrations to the Debye‐Waller factor for 57Fe atoms present as a dilute impurity in solid solution of aluminium are also estimated. The exponent of the Debye‐Waller factor is found to increase much more rapidly at higher temperature for a defect lattice than that for a perfect lattice due to the presence of the anharmonic terms in the expansion of the potential energy of the crystal.
Luminescence et structure vibrationnelle des luminophores CaS:Ce3+ et CaSe:Ce3+
Authors: Asano S. , Yamashita N. , Ogawa Y. 
Published: July 2007

AbstractExcitation and emission spectra for CaS:Ce3+ and CaSe:Ce3+ phosphors are measured at 6, 80, and 300 K. The vibrational structure on the emission bands 2T2g → 2F5/2, 2F7/2 and the excitation band 2F5/2 → 2T2g is analysed by the use of energy matrices in order to determine the coupling constant of spin‐orbit interaction ζf and the crystal field parameters V, V for the 4f orbit. In addition, some information on the transfer of the excitation energy from the host crystal to an unexcited Ce3+ ion is obtained by the aid of the diffused reflection spectra of CaS, CaSe, SrS, and SrSe phosphors containing no activator.
Picosecond Study of the Exciton Gas Cooling
Authors: Amand T. , Cornet A. , Pugnet M. , Collet J. , Brousseau M. , Razbirin B. S. 
Published: July 2007

AbstractThe exciton gas cooling in several materials. namely CdSe, CuI is investigated. The exciton gas temperature is measured directly from picosecond time resolved luminescence. It is shown that the cooling kinetics are well explained by emission of acoustical phonons by excitons. The lattice temperature is deduced, as well as the density of excitons created after the exciting laser pulse.
Tight‐Binding Cluster Model for C, Si, and Ge. II. Size and Shape Dependence of Some Cluster Properties
Authors: Künne L. , Skála L. , Bílek O. 
Published: July 2007

AbstractThe analytic description of the electronic structure of the s‐states tight‐binding cluster model of C, Si, and Ge (part I) is used for the investigation of the dependence of some electronic properties of the clusters on their size and shape. Clusters in the form of cubes, plates, and rods are considered. The rate of convergence of the cluster properties to the corresponding limit values is discussed.
Carrier Density near the Semiconductor‐Insulator Interface. Local Density Approximation for Non‐Isotropic Effective Mass
Authors: Paasch G. , Übensee H. 
Published: July 2007

AbstractFor bent bands in a semiconductor near the interface to an insulator, a modified local density approximation is described which takes into account the influence of the interface barrier in the potential. Simple expressions are obtained for the electron and hole densities in a multi‐valley semiconductor with non‐isotropic parabolic bands. Due to the interface barrier the densities decrease to zero towards the interface. The characteristic length for this decrease is determined by the effective mass tensor and by the orientation of the interface. Results of self‐consistent density calculations are reported.
Cooperative Jahn‐Teller Orbital Ordering in KCuF3 and K2CuF4 Crystals
Authors: Nikiforov A. E. , Shashkin S. Yu. , Levitan M. L. , Agamalyan T. H. 
Published: July 2007

AbstractTwo mechanisms of Cu2+ orbital ordering in KCuF3 and K2CuF4 are considered: the Jahn‐Teller and the exchange mechanisms with account of the crystal elastic energy. The Jahn‐Teller coupling constants and exchange parameters necessary for the evaluation of angles characterizing the orbital and crystal structures of crystals are estimated. It is shown that the exchange mechanism alone cannot explain the experimentally observed values of orbital structure angles. Within the frames of the Jahn‐Teller mechanism both, orbital and magnetic structures of KCuF3 and K2CuF4 are explained and the connection between the orbital structure angles of these crystals is established and also a qualitative explanation of the orbital structure angle values experimentally observed in MnF3 and KCrF3 is given.
On the Translation Mode of the Kink Lattice of a Quasi‐One‐Dimensional Peierls‐Fröhlich System with a Nearly Half‐Filled Band
Authors: Fischbeck H. J. 
Published: July 2007

AbstractThe translation mode of the kink lattice of a quasi‐one‐dimensional Peierls‐Fröhlich system in the continuum limit is investigated by means of the Landau expansion of the thermodynamic potential. An expression for the sound velocity is given and numerically evaluated.
The Rôle of Two‐Level Systems in Amorphous Metallic Alloys. I. Induced Anisotropy in Amorphous Ferromagnets
Authors: Kronmüller H. 
Published: July 2007

AbstractThe induced anisotropy in amorphous ferromagnets is attributed to the directional ordering of atom pair axes. The thermodynamics and micromagnetic background of this process is treated on the basis of two‐level systems which are identified with mobile atom pairs in the neighbourhood of free volumes. The rǒle of ‘reversible’ and of ‘irreversible’ relaxation processes is discussed in detail.