bluuebunny/crossref_metadata_2025_split huggingface dataset:
The coexistence of unstable, metastable, and separated Frenkel pair defects in solids. III. Theory of the non‐impact mechanisms for defect formation in non‐metals
Authors: Dzhumanov S. , Khabibullaev P. K. 
Published: July 2007

AbstractA general theory is developed of non‐impact mechanisms of the unstable (U), metastable (M), and separated (S) Frenkel pair defect creation in non‐metals that is realized at the decay of excitons, electron‐hole (e‐h) pairs, and holes. A two stage self‐trapping model of excitons (holes) is proposed. The initial stage of self‐trapping is considered in the framework of a simple continuum model and its final stage in the framework of a quasi‐molecular model. The formation of a quasimolecular type self‐trapped exciton (STE) is followed by its spontaneous transition or by the transition with overcoming the potential barrier from centrosymmetric (CS) to different off‐centrosymmetric (OCS) positions. In this configuration the dynamic displacement and dissociative decay of an STE molecular ion with the creation of Frenkel pairs become possible. The direct displacement possibility of an STE molecular ion from the CS to an interstitial position is also analysed. The reasons of the low efficiency of Frenkel pair creation in alkali halides at the decay of e‐h pairs and holes is clarified. The possibility is shown of STE decay into the neutral U, M, and S anion Frenkel pairs as well as into the charged U and M cation Frenkel pairs. The theory proposed explains satisfactorily all the experimental data available.
Complete order parameter condensate of low‐symmetry phases upon structural phase transitions
Authors: Chechin G. M. , Ivanova T. I. , Sakhnenko V. P. 
Published: July 2007

AbstractA group‐theoretical method within the framework of the Landau theory of phase transitions is proposed to obtain and analyse a complete set of critical (primary) and noncritical (secondary) order parameters condensing as a result of a phase transition (complete condensate). The principal problems that can be solved by this method are formulated. A number of theorems describing the structure of complete condensate are proved. As an example, phase transitions are examined in crystals having O(Fd3m) space symmetry induced by six‐dimensional irreducible representations.
An XPS study of chemical order in hydrogenated amorphous silicon‐carbon alloy films
Authors: Smith G. B. , McKenzie D. R. , Martin P. J. 
Published: July 2007

AbstractThe Si(2p) and C(ls) XPS spectra of a‐Si1‐xCx: H films are studied before and after argon ion etching. Two specimens, with x = 0.26 and x = 0.39 are prepared by glow discharge decomposition of SiH4 and CH4 gases diluted in hydrogen. The as‐prepared specimens show adsorbed free carbon and silicon oxides which are substantially removed by ion etching. Both specimens indicate a preference for bonding between Si and C atoms, even after the randomizing effect of the ions. The specimen with x = 0.39 shows essentially complete chemical order while the other specimen shows some carbon not bonded to silicon as well as a substantial amount of silicon not bonded to carbon. The results agree with electron diffraction observations on the same specimens.
Photoemission on AB semiconductor material. Cd3As2, Zn3As2, Cd3P2, Zn3P2 crystals and thin films
Authors: Hupfer A. , Hirsch D. , Schulze S. 
Published: July 2007

AbstractThe density of valence states of sputter‐annealed Cd3As2, Zn3As2, (Cd0.54Zn0.46)3As2, Cd3P2, and Zn3P2 crystals as well as in situ UHV deposited Cd3As2 and Zn3P2 thin films are determined with UV (He/Ne I, II) and X‐ray (Zr Mζ, Al/Mg Kα) photoemission. Some AB valence electron density of states data reported in literature and measured by X‐ray emission and UP/XP spectroscopy are verified by the experiments. All AB materials studied provide UPS/XPS curves, which are qualitatively similar to those reported for AIIBVI compounds.
X‐ray photoelectron spectra of high Tc bismuth compounds. General trends for layer structures
Authors: Bocquet A. E. , Dobson J. F. , Healy P. C. , Myhra S. , Thompson J. G. 
Published: July 2007

AbstractAnalysis by XPS and XAES has been carried out for Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 HTSC compounds. Some preliminary results are also reported for a Tl specimen with predominant Tl2Ba2CaCu2O8 stoichiometry, as well as La0.6Sr0.4CoO3 which is a “metallic” oxide, but is not superconducting above 4.2 K. Anomalous low binding energy contributions are found for the main alkaline earth envelopes (Ba 3d, Ca 2p, and Sr 3d) for all of these compounds. Likewise, two distinct contributions to the O 1s envelope are observed. The Bi and Tl 4f envelopes and binding energies are consistent with these species being subject to metallic screening. Possible implications of these observations for the electronic structure of the layered HTSC oxides are discussed in the context of a “screening” as well as a “shake‐down” model.
AC conductivity of inhomogeneous semiconductors in the presence of classically high magnetic field
Authors: Chaikovskii I. A. , German A. I. 
Published: July 2007

AbstractResults are given of a calculation of the transverse effective ac conductivity, σ(ω), in electrically in homogeneous semiconductors in the presence of a classically high magnetic field H (ω is the frequency of the alternating electric field). The expressions for σ(ω) are obtained with the aid of summation of diagrammatic series. It is shown that in the frequency range ωτM ≪ ξ2/3β−4/3 (τM is the Maxwell relaxation time; β = μH/c; μ the carrier mobility; ξ = 〈(n(r) − 〈n〉)2〉/〈n〉2; n(r) is the local value of the carrier density; 〈n〉 its mean value) σ (ω) ∝︁ H−4/3, and when ωτM ≈ ξ2/3β−4/3 there should be a change in the dependence on H. When ωτM ⪆ ξ2/3β−4/3, σ(ω) ∝︁ HP−2 like in an homogeneous sample.
Non‐equilibrium velocity autocorrelation function for semiconductors in the presence of trapping phenomena
Authors: Macucci M. , Pellegrini B. , Terreni P. , Reggiani L. 
Published: July 2007

AbstractThe velocity autocorrelation function is calculated analytically in the presence of an external electric field for a simple model semiconductor when both, generation‐recombination and scattering processes take place. The analytical theory, which follows a standard probability calculation, is complemented by an appropriate Monte Carlo simulation. Both, analytical and numerical results, by accounting for the interaction between different processes, are found to generalize existing approximate solutions. In the presence of increasing fields the velocity autocorrelation function is found to exhibit long‐time tails, due to generation‐recombination processes, as well as a significant increase of the square mean value of the velocity because of the onset of hot‐electron effects.
Tensor fields in crystals and band representations of space groups
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractThe connection between tensor field and band representations of space groups is established. A tensor field representation is a direct sum of several simple band representations. Its irreducible components are easily found from the tables of simple band representations. The vibrational tensor field representations for some high‐Tc superconductors are considered in this context.
The Generalized Fractals and Statistical Properties of the Pore Space of the Sedimentary Rocks
Authors: Nigmatullin R. R. 
Published: July 2007

AbstractA new class of fractals with random values of scales are developed. In accordance with a statistical self‐similarity principle the probability distribution function of scales is found. The formulae for fractal porosity are obtained and a comparison with recent experiments is made. A new expression for a fractal component “containance” in polyphase systems is obtained.
Three‐Body Force and Shell Model Contributions to Third‐Order Elastic Constants for Fluorite Structure Crystals
Authors: Singh R. , Shanker J. 
Published: July 2007

AbstractExpressions for the third‐order elastic constants of fluorite structure solids are derived by taking into account the three‐body forces and inter‐sublattice displacement through the shell model. The third‐order elastic constants and pressure derivatives of second‐order elastic constants are calculated for CaF2, SrF2, BaF2, and their mixed crystals. The results obtained with the help of present model show satisfactory agreement with experimental values.
Thermodynamic Parameters of Anti‐Frenkel Formation in Alkaline Earth Fluorides
Authors: Haridasan T. M. , Sekar P. 
Published: July 2007

AbstractThe entropy of formation of anti‐Frenkels in CaF2, SrF2, and BaF2, at constant volume is computed using the Green's function technique. The results on the constant pressure quantities of enthalpy, formation volume, and Gibbs free energy are presented.
Order–Disorder Model of Phase Transition in AxB1−x Binary Systems of F.C.C. Structure
Authors: Wang Qiang , Zhang Xiao‐Wen , Gu Bing‐Lin 
Published: July 2007

AbstractBy means of the cluster variation method, and introducing the nearest‐neighbour interaction, a phase diagram of the AxB1−x binary system with f.c.c. structure is obtained. A calculation of the lattice parameters versus composition is carried out, and the results show that the formation of an amorphous alloy in an immiscible FeCu system could be attributed to the lattice deformation.
A Quantized Screening Theory for the Surface Energy of Solids in the Hydrodynamic Jellium Model
Authors: Babiker M. , Cottam M. G. 
Published: July 2007

AbstractA simple model for the surface energy of solids in the jellium model is described, based on the modifications of the screening properties in the presence of a free surface. In contrast to the case in the bulk, a constituent charge and its screening cloud will acquire position‐dependent electric multipole distributions. The interaction of these with the free longitudinal polarization field gives a measure of the surface energy of the solid. The calculations are presented within the dispersive hydrodynamic (jellium) approximation taking two alternative forms of the boundary condition. The applicability of this theory to the surface energy of metals is discussed.
Macroscopic Electrodynamics of Ultra‐Thin Films
Authors: Khudik B. I. , Lozovskii V. Z. , Nazarenko‐Bary Akhtar I. V. 
Published: July 2007

AbstractAn approach, based on the Green's function method, for constructing the ultra‐thin film electrodynamics is developed. The electrodynamics Green's functions of the isolated dielectric film as well as of the substrate are constructed. The dispersion laws of the electromagnetic waves on the films are investigated.
Density of States in Transition Metal–Metalloid Amorphous Alloys
Authors: Jezierski A. 
Published: July 2007

AbstractThe electronic density of states in transition metal–metalloid non‐crystalline alloys is calculated using the recursion method and the tight binding linear muffin tin orbital method. In the total density of states the main peak is observed near the Fermi energy. The density of states at the Fermi energy in Ni0.7B0.3(1−x)P0.3x non‐crystalline alloys decreases with increasing concentration of phosphorus.
Ground State of the Gd3+ Ion in MF2 Single Crystals under the Influence of an External Static Electric Field
Authors: Guskos N. 
Published: July 2007

AbstractThe quadratic electric field effect for cubic Gd3+ centers in MF2 single crystals is discussed in terms of the quasimolecular and superposition model. Very high electric fields (above 300 kV/cm) are required to observe this effect. Zero‐field splitting of Gd3+ ions in the crystal field is also discussed. It is shown that these models interpret the changes in the induced B spin‐Hamiltonian parameter consistently.
On the Theory of Conduction of Antiferromagnetic Semiconductors
Authors: Karpenko B. V. , Kuznetsov A. V. , Falkovskaya L. D. 
Published: July 2007

AbstractThe kinetic properties of an isotropic antiferromagnetic nondegenerate semiconductor in a high electric field are investigated theoretically. By solving a system of kinetic equations for electrons and magnons a nonequilibrium electron distribution function is found. It is shown that under certain conditions the volt–ampere characteristic calculated with the use of this function may have an N shape.
Electrical Conductivity, Magnetic Susceptibility, and Infrared Spectra in the Superconducting Systems BiSrCaCuO and TlBaCaCuO
Authors: Gruber H. , Krautz E. , Fritzer H. P. , Gatterer K. , Popitsch A. 
Published: July 2007

AbstractSince the properties of the high temperature superconducting systems TlBaCaCuO and BiSrCaCuO depend very sensitively on composition and structures various preparation methods are applied and the products are tested by measuring the transport and magnetic susceptibility properties together with their IR‐spectra. Most samples show multiphase structure. The highest transition temperature with zero resistance Tco ≈︁ 125 K, is found in the system TlBaCaCuO, which is lowered to Tco ≈︁ 102 K in the case of doping with Ag.
Elementary Excitations in Two‐Sublattice Spin Model with Three‐Ion Interaction
Authors: Lipowski A. , Onyszkiewicz Z. 
Published: July 2007

AbstractA two‐sublattice spin model (S = 1) with three‐ion interactions besides the usual exchange terms is investigated. By means of standard basis‐operator representation within the high density expanison method, formulae for the temperature‐depedent spectra of elementary excitations are obtained. The results in the limit T → 0 are compared with the experimental spectrum of elementary excitations for field‐induced metamagnet FeCl2.
Lattice Distortion‐Induced Quadrupole Interactions, Phases, and Excitations in J = 1 Tetragonal Paramagnets
Authors: Ulner J. , Durczewski K. 
Published: July 2007

AbstractA quadrupole‐quadrupole Hamiltonian for a deformed J = 1 paramagnet of f‐shell localized effective magnetic moments (rare earths, actinides) is derived. The Hamiltonian includes all the interactions between the relevant quadrupole operators and corresponds in particular cases to purely phenomenological Hamiltonians obtained by symmetry considerations. The molecular field and equation‐of‐motion method is applied for studying the system described by this Hamiltonian in the case of the doublet–singlet crystal field splitting in the quadrupolarly disordered phase of the phase diagram.
Radiation Induced Luminescence from Dipoles Immersed in a Solid with a Rough Surface
Authors: Nkoma J. S. 
Published: July 2007

AbstractLuminescence is modelled as radiation from an oscillating dipole immersed in a solid with a rough surface. Maxwell's equations are solved and the zero order and first order electric fields in the roughness amplitude are obtained. It is found that the first order contribution becomes comparable to the zero order contribution only when the roughness amplitude is large, of the order of 1000 nm. The effects of dipoles oriented parallel and normal to the z‐axis are compared. The results are applied to a system of GaP with a rough surface and bounded by vacuum.
On the Excitation and Emission of the Infrared Luminescence of Wide Band Gap Mn II–VI Semimagnetic Semiconductors
Authors: Benecke C. , Busse W. , Gumlich H.‐E. , Hoffmann H. , Hoffmann S. , Krost A. , Waldmann H. 
Published: July 2007

AbstractThe IR emission and the corresponding low energy excitation spectra of the wide band gap semimagnetic semiconductors Zn1−xMnxTe, Cd1−xMnxTe, Zn1−xMnxSe, Cd1−xMnxSe, Zn1−xMnxS, and Cd1−xMnxS are critically discussed in the light of the models proposed until now. The similar shape of these spectra and the comparison with the spectra due to Mn in tetrahedral coordination lead to the conclusion that the longwave emission and excitation bands of these substances can tentatively be interpreted as due to cubically coordinated Mn2+ ions on interstitial sites or in octahedrally coordinated MnTe, MnSe, and MnS cluster. The crystal field parameters B, C, and Dq of these Mn2+ ions (Td or Oh symmetry) are determined on the basis of the experimental data.
Structural Studies of Charged Hard‐Sphere Mixtures through Blum's Generalized “Γ” Parameter. Application to Molten RbCl and RbBr
Authors: Rao R. V. Gopala , Satpathy A. 
Published: July 2007

AbstractThe most general solution for the direct correlation function of unequal diameters for charged hard‐sphere mixtures is given by Blum and Tibavisco in the mean spherical model approximation. Hiroike has given expressions for Cij(r), the direct correlation function (DCF), in a form convenient for numerical caluculations. These equations are used in the evaluation of partial structure factors of RbCl and RbBr. The DCF expressions contain a parameter Γ which is analogous to the Debye inverse length parameter. This parameter is calculated numerically. From the partial structure factors, the partial radial distribution functions, the co‐ordination numbers, charge–charge and number–number correlation functions are obtained. Also computed are the compressibilities from the partial structure factors in the long wave limit, which are in satisfactory agreement with literature values. For the case of RbCl no literature values are available. – The present method is different from the previous ones in the sense that it requires a minimum number of parameters, namely the ionic diameters. It is found that this model reproduces all the characteristics of fused salts, and the results compare satisfactorily with experiment.
Plane Wave Diffraction by a Deformed Crystal
Authors: Kulda J. , Lukáš P. 
Published: July 2007

AbstractThe dynamical description of neutron propagation in distorted crystals is reconsidered for cases of small deformation gradients where the effect of interbranch scattering (creation of new wavefields) remains negligible. Under such conditions the neutron eigenfunctions in both, transparent and absorbing crystals follow adiabatically the variation along the beam path of the deviation from the Bragg condition. With their help the rocking curve is derived explicitly for the symmetrical Laue case and the extension to asymmetrical geometries is discussed in detail. The resulting formulas, though lengthy, posses a simple enough structure to facilitate qualitative as well as quantitative discussions of the behaviour of the Pendellösung oscillations and anomalous transmission under the influence of deformation or of external fields on the diffracting neutrons.
The Sink Strength of Dislocation Dipole and Low‐Angle Tilt Boundary
Authors: Galimov R. R. , Goryachev S. B. 
Published: July 2007

AbstractA method is proposed for calculating the sink strength of dislocation ensembles with an allowance for the stress elastic interactions between point defects and dislocations. The method is based on the use of the radius of the activationless capture of a point defect by the elastic field of the sink (dislocation or ensemble as a whole). The value of the radius is about the spacing at which the interaction energy becomes equal to the thermal energy of a point defect. The expressions for the sink strength of the simplest dislocation ensembles (a dislocation dipole and a low‐angle tilt boundary) are obtained and analysed.
A Nonlocal Continuum Approach to the Dynamics of Crystals. II. B.C.C. Lattice
Authors: Idiodi J. O. A. , Lee Yinggang 
Published: July 2007

AbstractA continuum approach to lattice dynamics, incorporating effects of nonlocality, is developed. This is an extension to the b.c.c. lattice of a previous work which dealt mainly with the s.c. and f.c.c. lattices. In the treatment of the boundary conditions that arise in the presence of a surface, one is able to exhibit the rich possibilities that are accessible to the general and unified treatment presented here. It is most unlikely that the extra structure identified in the boundary conditions, as compared to several other treatments in the literature, would make a null contribution to various theoretical predictions in the dynamics of solid surfaces. In the appropriate limits the formalism passes over to the conventional elastic continuum theory.
Vibration Spectra and Phase Transitions in Layered Semiconducting Ferroelectrics with TlGaSe2 Structure. II. Thermodynamic Description of Phase Transitions
Authors: Goncharov Yu. G. , Kozlov G. V. , Kulbuzhev B. S. , Shirokov V. B. , Torgashev V. I. , Volkov A. A. , Yuzyk Yu. I. 
Published: July 2007

AbstractA thermodynamic theory of phase transitions in crystals with TlGaSe2 structure is developed. The nature of order parameters is discussed on the basis of spectroscopic data. A phase diagram is constructed in the plane of the model coefficients. Conclusions are made to the trigger character of the phase transitions observed at low temperatures.
On the Mean Square Displacements (MSD) of Hg and Te in HgTe
Authors: Madhavan Y. , Ramachandran K. , Haridasan T. M. 
Published: July 2007

AbstractThe mean square displacements (MSD) of Hg and Te in the perfect system of HgTe are worked out in the modified rigid ion model of Plumelle and Vandevyver. Also the MSD of Hg and Te neighbours around anion and cation vacancies in HgTe are worked out giving an active role for the vacancy following the theory of Maradudin et al. The results are compared with experimental values.
Exciton Transfer between Localized States in CdS1–xSex Alloys
Authors: Gourdon C. , Lavallard P. 
Published: July 2007

AbstractPicosecond time resolved luminescence is investigated of excitons localized by alloy potential fluctuations in CdS1–xSex. Time resolved luminescence spectra, as well as time decay curves and time integrated luminescence spectra of a CdS0.36Se0.64 sample are fitted using a model in which transfer to lower energy states occurs through the tunnel effect assisted by acoustic phonons. The density of states is taken to be exponential with a characteristic energy, E0, equal to 2.2 meV. The radiative lifetime is 1.5 ns. The nonradiative lifetime due to transfer is inversely proportional to the number of available states at lower energy. Close agreement with the experimental results can also be found with a phenomenological model.
Résonance magnétophonon avec retournement de spin dans l'antimoniure d'indium
Authors: Galibert J. , Perrier P. , Askenazy S. 
Published: July 2007

AbstractNous rendons compte dans cette lettre de la première mise en évidence de la transition fondamentale entre les niveaux résolus en spin 0−0+ dans InSb, qui prouve de manière indubitable l'existence dans ce matériau, de transitions avec retournement de spin induites par phonons.
Effects of Hydrostatic Pressure on the Cu+ Center in Potassium Halides
Authors: Emura S. , Ishiguro M. 
Published: July 2007

AbstractIt is found that a Cu+ center in KBr single crystals shows a new emission peak at 335 nm and a new absorption peak at 245 nm, when high pressure is applied to the crystal. These peaks show amazing temperature and pressure dependences as follows: a) The new peaks are observed under application of pressure after cooling the crystal. b) When the crystal is pressed prior to cooling, the new peaks do not appear. c) The new peaks can be observed, if the pressure is removed below 190 K. d) The emission intensity increases with temperature under the fixed pressure, while the absorption intensity reduces gradually. e) The new peaks disappear when the crystal is warmed higher than around 210 K. Similar results are observed both in KCl and KI as well as in KBr. The change of the off‐center behaviour from a deep off‐center to a shallow one due to the applied pressure is observed. The relation of the Cu+ position and its ionicity is discussed.
Electronic Structure and Magnetooptical Effects in γ‐Ln2S3
Authors: Babonas G. , Dagys R. , Pukinskas G. 
Published: July 2007

AbstractFaraday rotation and magnetooptical polar Kerr effect are studied in γ‐Ln2S3 crystals. The peculiarities of the magnetooptical spectra in Ln2S3 are interpreted on the basis of the regularities of f–f and f–d transitions in free Ln3+ ions taking into account the mixing of the excited localized and band states.