bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative Magnetoresistance in Zinc Selenide
Authors: Ivanova G. N. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractThe effect of negative magnetoresistance (NMR) is found and studied in low‐ohmic n‐ZnSe crystals with electron concentrations from 2.1 × 1016 to 4.9 × 1017 cm−3 which is manifested as a reduction in resistance of the crystals in the magnetic field. The investigations are made in the temperature range 1.65 to 300 K. Basic regularities of NMR in specimens with an electron concentration of about 1017 cm−3 are well correlated with the Toyozawa theory developed on the assumption that in the impurity band of a semiconductor states exist partly filled with electrons. The relation between NMR and temperature and magnetic field for these specimens is described by the Curie‐Weiss law down to the Néel temperature TN = 2 K; at lower temperatures a deviation is observed. A relationship between the localized magnetic moment and magnetic field is found and explained. In lightly doped n‐ZnSe crystals where the impurity conduction is of hopping nature, the NMR effect is explained qualitatively on the assumption that the magnetic field affects the density of states near the Fermi level.
Temperature Dependences of the Nonradiative Multiphonon Carrier Capture and Ejection Properties of Deep Traps in Semiconductors. II. Interpretation and Extrapolation of Capture Data
Authors: Pässler R. 
Published: July 2007

AbstractOn the basis of our semiempirical theory of nonradiative multiphonon (NMP) carrier capture processes a numerical analysis and extrapolation of experimental data on electron capture coefficients of the third acceptor level of copper and the second acceptor level of gold in germanium is made. The associated configuration coordinate diagrams are determined. From the correlation between NMP electron and hole capture properties follows that the NMP mechanism for hole capture is comparatively little effective (at usual temperatures). The activation of NMP carrier capture by thermal motion of the lattice is found to be more pronounced than suggested by Sinyavskii and Kovarskii. the uncertainties inherent to extrapolations up to very high temperatures are shown analytically to be much larger than expected by Henry and Lang. The high‐temperature capture cross‐sections of the traps under study are estimated to lie within the range 10−16 to 10−14 cm2. A modification is presented of the analytical apparatus adequate for numerical applications in the ranges of low and intermediate temperatures.
Jahn‐Teller‐Type Phase Transitions in Solids during Laser Irradiation
Authors: Wautelet M. 
Published: July 2007

AbstractStrong laser irradiation is shown to modify the characteristics of the Jahn‐Teller distortion in solids. In particular, the static distortion is reduced, together with the Jahn‐Teller energy. This is due to the influence of the electronic term included in the total energy of the system, which changes with the relative populations of the fundamental and excited states.
Theory of Spin–Phonon Interactions in a System of Paramagnetic S = 3/2 Ions
Authors: Psaltakis G. C. , Cottam M. G. 
Published: July 2007

AbstractCalculations are presented for the thermodynamic properties and the excitation spectrum of an interacting spin–phonon system with S = 3/2. A diagrammatic technique is employed based on a recent generalisation of the drone‐fermion representation for S > 1/2. Corrections to the free energy and to the specific heat are calculated, including contributions up to second order in the spin–phonon interaction. Estimates are given for Cr3+ ions in MgO. The dispersion relation of the coupled spin–phonon modes is also evaluated in second order.
Lattice Dynamics of [Ni(NH3)6] (ClO4)2, [Ni(NH3)6] (BF4)2, and [Ni(NH3)6] (PF6)2
Authors: Kulczycki A. 
Published: July 2007

AbstractThe lattice dynamics of crystalline [Ni(NH3)6] (ClO4)2, [Ni(NH3)6] (BF4)2, and [Ni(NH3)6] (PF6)2 is studied in the framework of the point charge model. Phonon frequencies, in six high‐symmetry directions, and elastic constants are calculated. Good agreement with the experimental data for Raman active frequencies is achieved.
Intrinsic Glide Resistance on {100} Planes in Alkali Halides
Authors: Suzuki T. , Skrotzki W. , Haasen P. 
Published: July 2007

AbstractIn the alkali halides the critical resolved shear stress for slip on {100} planes becomes strongly temperature dependent below a critical temperature. In addition the activation volume decreases below 100b3 (b Burgers vector). This behaviour can be explained in terms of a large intrinsic resistance to dislocation motion on this slip plane. The Peierls stresses for {100} slip are of the order of 10−2 c44 (c44 shear modulus for the {100} plane).
On the Luminescence of Some s2‐Ion‐Activated Alkaline‐Earth Phosphates
Authors: van der Steen A. C. , Aalders Th. J. A. 
Published: July 2007

AbstractThe luminescence properties of β‐Ca3(PO4)2:Tl+, β‐Ca3(PO4)2:Bi3+, and α‐Sr3(PO4)2:Sn2+ are reinvestigated. The emission spectrum of β‐Ca3(PO4)2:Tl+ consists of two bands which can be ascribed to a Jahn‐Teller effect in the excited state of the Tl+ ion. The emission spectrum of Bi3+‐activated β‐Ca3(PO4)2 shows vibrational structure. The 3P0 emission of the Sn2+ ion in α‐Sr3(PO4)2 can only be observed at very low temperatures. The trap depth amounts to 23 cm−1.
Energy Band Structure and Electronic Properties of NiAs Type Compounds. II. Antiferromagnetic Manganese Telluride
Authors: Sandratskii L. M. , Egorov R. F. , Berdyshev A. A. 
Published: July 2007

AbstractThe first calculation of the electron energy spectrum of antiferromagnetic MnTe is made using Green's function method. In accordance with the experiment MnTe is found to be a semiconductor with an indirect gap ≈0.8 eV and a direct gap of ≈1.26 eV. The results obtained confirm the validity of Allen's qualitative model for the MnTe energy structure. Special moments of symmetry are discussed. The semiconductor character is shown to be connected with antiferromagnetic order. The effective masses of valence band top electrons are calculated in the kp approximation and compared with the experiment.
Charge Carrier Detrapping by Triplet Excitons
Authors: Petelenz P. 
Published: July 2007

AbstractVarious possible channels of charge carrier detrapping by triplet excitons via exciton and/or charge transfer are considered. It is concluded that the charge transfer mechanisms are much more feasible than the direct excitation transfer. If the transport in the neighbourhood of the trapped charge is coherent, the dominating detrapping channel is expected to be that proceeding via a virtual CT state. The possible experimental consequences are discussed and new experiments are suggested.
Neutron Scattering Studies on Phase Transitions and Phonon Dispersion in CsSrCl3
Authors: Prokert F. 
Published: July 2007

AbstractThe successive phase transitions (PT) of CsSrCl3 which belongs to the family of the cubic perovskites of the type ABX3 are investigated by inelastic neutron scattering. At first the acoustic phonon dispersion is measured in the cubic phase near the first PT. Outgoing there from it is possible to determine the sequence of the phonon mode condensation by evaluating the temperature dependence of the quasi‐elastic and Bragg scattering at the zone boundary points (M, R, and X). From the results of neutron scattering it is obvious that the PT into the tetragonal phase is caused by a condensation of a M3‐mode and that the characterization of the successive PT's, proposed originally by Alexandrov et al. is the correct one.
Phonon Modes and Infrared Absorption in the Coupled System Film–Substrate
Authors: Grosse H.‐H. , Jäger E. , Telloke U. 
Published: July 2007

AbstractThe system optical film–substrate and its vibrational modes are investigated with the help of the simple model of two coupled diatomic linear chains. It is possible to derive an analytical equation for the determination of the frequencies. But this equation can be solved only numerically. The vibrational modes, their frequencies, and the absorption in the infrared are discussed, especially the influence of the interchain coupling constant on these quantities.
External and Internal Strains in Piezoelectric Crystals
Authors: Munn R. W. 
Published: July 2007

AbstractA generalized thermodynamic theory is used to give expressions for the internal strains induced in piezoelectric crystals for given external strains produced either at constant stress or at constant electric field; only certain combinations of strains can be produced by electric fields. Previous results for the zinc blende structure are shown to follow from the general treatment, which is readily applied to any crystal structure or microscopic model.
Plasmon Dispersion in Lithium for Large Wave Vectors
Authors: Tripathy D. N. , Pal R. K. 
Published: July 2007

AbstractUsing Bohm‐Pines Hamiltonian for the electron‐plasmon system the one plasmon propagator is evaluated, the poles of which determine the plasmon frequency. It is found that the interaction term bilinear in the plasmon coordinates mostly give rise to a negative shift to the classical plasma frequency ωpl at k = 0. Redefining the critical wave vector kc used in the random phase approximation (RPA) the observed plasmon frequency of ≈ 0.9 ωpl at k = 0 in Li is reproduced. The new critical wave vector is found to be much larger than k implying that the plasmons continue to exist beyond k. The calculations for the dynamic structure factor corresponding to the plasmon excitations, Spl(k, ω), show that this has a Gaussian form for momentum transfer larger than ≈ 0.4kF. Adding to this the dynamic structure factor for the quasi‐particle excitations, it is possible to observe a structure in the total S(k, ω) near k ≈ k. The plasmon dispersion and line‐width estimated from the theory for Li are found to agree fairly well with those of the experiments.
On the Problem of Vibrational Surface States in Strongly Anisotropic Crystals with Uniaxial Long‐Range Interaction
Authors: Petrova T. G. , Syrkin E. S. 
Published: July 2007

AbstractThe influence of strong uniaxial anisotropy on the vibrational states of an infinite crystal is studied. Interatomic interactions along the direction of anisotropy are assumed to be of long‐range type. It is found that the anisotropic interaction creates the additional gaps between the bulk bands of frequencies and brings about new localized surface modes inside these gaps as compared to the isotropic case. The frequencies and damping decrements of the gap surface waves are obtained.
Excitation Spectra of Disordered Systems. I. General Theory
Authors: Chen Y. C. , Wu Shi‐Yu , Sinai J. J. 
Published: July 2007

AbstractThe approximate method developed by Wu for the study of the lattice dynamics of one‐dimensional disordered systems is extended to be applicable to two‐ and three‐dimensional systems. The basic ideas of the approach are reviewed and the multi‐dimensional form of the approximation is developed. Applications are made to periodic lattices in all dimensions and the one‐dimensional disordered lattice. Comparisons with previous results show excellent agreement.
Paramagnetic Broadening of PMR Line in Ammonium Manganese Sulphate
Authors: Kapturczak J. , Pająk Z. 
Published: July 2007

AbstractFrom the angular and temperature dependences of the second moment of single crystal and polycrystalline AMS, a new effect of paramagnetic line broadening for protons of ammonium ions is evidenced. The possible sources of apparent local fields, characterized by the distribution parameter introduced, are discussed.
Isothermal and Frequency‐Dependent Perpendicular Susceptibilities of the One‐Dimensional Ising Model with Nearest and Next‐Nearest Neighbour Interactions
Authors: Goncalves L. L. 
Published: July 2007

AbstractExact expressions for the isothermal and frequency‐dependent perpendicular susceptibilities are obtained for the Ising model (s = 1/2) with nearest and next‐nearest neighbour interactions under zero external field. The static correlations are obtained by mapping the model in a pseudo Ising model with nearest‐neighbour interactions under an external field. The difference between the isothermal and isolated susceptibilities is discussed.
Lattice Green's Function for Thin Films. The S.C.(001) Thin Film Green's Function
Authors: Wachniewski A. 
Published: July 2007

AbstractThe lattice Green's function for thin films is defined by modifying the usual definition of the lattice Green's function for bulk crystals. This definition comprise the thin film wave functions and quantum numbers. The general case of complex boundary parameters (i.e. complex surface energies) is considered and the corresponding formulas for the wave functions are derived. For the s.c.(001) thin film the lattice Green's function is given as a sum of finite number of terms each of which includes a complete elliptic integral of the first kind. The results of the numerical calculation obtained with aid of this formula are shown by graphs.
High Magnetic Field Observation of the Resonance Donor States of S in InSb
Authors: Porowski S. , Konczewicz L. , Kowalski J. , Aulombard R. L. , Robert J. L. 
Published: July 2007

AbstractElectrical transport measurements in InSb heavily doped with sulfur (n ≈ 5 × 1018 cm−3) are performed. At T = 4.2 K the Hall coefficient and transverse magnetoresistivity are measured as a function of pressure up to 2100 MPa and magnetic field up to 18 T. At the highest pressure, a decrease of the frequency and a decrease of the damping of Shubnikov‐de Haas oscillations are observed. These effects are explained as a result of the transfer of electrons from the conduction band to the resonance states of sulfur. At atmospheric pressure these states are 0.55 eV above the bottom of conduction band. In the lower pressure range, the experimental dependence of the effective Dingle temperature TD* = TD + Ti can be explained by the model in which the scattering by ionized impurities and short‐range potentials are taken into account. At the highest pressures a change of inhomogeneity of carrier concentration due to the transfer of electrons to the resonance states has to be considered.
Lattice Dynamics of ZrC Using Keating's Approach
Authors: Murty J. V. S. S. Narayana , Rao R. Ramji 
Published: July 2007

AbstractKeating's model is extended to work out the lattice dynamics of ZrC which crystallises in the rocksalt structure. The lattice specific heat is calculated using the frequency distribution function obtained on the present model. The agreement with the experiment is good.
Impurity‐Associated Colour Centres in Mg‐ and Ca‐Doped Al2O3 Single Crystals
Authors: Kulis P. A. , Springis M. J. , Tale I. A. , Vainer V. S. , Valbis J. A. 
Published: July 2007

AbstractIn Mg‐ and Ca‐doped α‐Al2O3 crystals irradiated by X‐rays at 80 K new paramagnetic colour centres are observed having an absorption band at about 255 nm and an emission band at 310 nm. The hyperfine structure of the EPR spectrum indicates that the unpaired electron spin interacts mainly with two Al27 nuclei. The optical and EPR spectra are consistent with the model of a centre involving one electron trapped at an anion vacancy adjoining the substitutional divalent ion (FMg or FCa). The luminescence band at 290 nm observed in the TSL peak at 225 K is suggested to result from the recombination of the holes with the FMg(FCa) centres.
A Statistical‐Pseudopotential Approach to the Calculation of Atomic Short‐Range Order in Solid Solutions
Authors: Khwaja Farid A. , Razmi M. S. K. 
Published: July 2007

AbstractA method to calculate the atomic short‐range order (SRO) for any number of coordination spheres is described in the framework of a statistical‐pseudopotential approximation. Calculations are carried out using second‐and third‐order perturbation expansion of the ionic potential for Al–10 at% Zn, Ni3Fe, and a series of Ni and Pt solid solutions. The numerical results obtained for the SRO parameters on the first three coordination spheres in the two cases are compared with the experimentally measured values. It is found that the third‐order theory gives a reasonable agreement with experiment.
On the Optical Properties and Electronic Structure of Solid Solutions of (Agx/2Pb1–xSbx/2)Te Type
Authors: Baleva M. , Stoyanov S. D. 
Published: July 2007

AbstractThe reflectance spectra in the energy range 0.4 to 4.0 eV at 300 K and thermoreflectance spectra in the energy range 1.0 to 4.0 eV at 70 and 240 K of solid solutions of (Agx/2Pb1–x·Sbx/2)Te type for x=0.2, 0.4, and 0.6 are obtained. On the basis of these measurements some conclusions about the change of the electronic band structure with the composition on going from PbTe to the AgSbTe2 zone are given.
Exciton Thermoabsorption of GaSe1−xSx Solid Solutions
Authors: Angelini V. , Casalboni M. , Grandolfo M. , Vecchia P. 
Published: July 2007

AbstractResults are reported obtained at liquid nitrogen temperature by thermally modulating the absorption of GaSe1−xSx solid solutions. In order to clarify the relations among different polytypes, their optical properties, and growth methods, a complete series of measurements is performed, varying the compositional parameter x from 0 to 1, for single crystals grown both from the vapour and from the melt. The results are consistent with the existence of a unique polytype (ε) for x ≈ 0 in crystals grown by both methods. Discontinuities in the exciton ground state energy E0 versus x curves are related to interpolytype transitions, namely γ → β andε → β, for melt‐ and vapour‐grown crystals, respectively.
Paramagnetic Spin Relaxation Due to Spin—Spin Interaction Assisted by Spin—Phonon Interaction or Vice Versa (II)
Authors: Srivastava K. K. P. , Singh H. C. 
Published: July 2007

AbstractFor paramagnetic ions the electronic spin—spin and spin—lattice relaxations taking place independently are well known. In the first part of this paper a new type of “mixed spin relaxation process” has been considered in which dipolar spin—spin and spin—phonon (or orbit—lattice) interactions are jointly needed to effectively produce a relaxation transition, and the rate‐expression for this process has been obtained on phenomenological considerations. In this part of the paper the “mixed spin relaxation rates” for substitutional paramagnetic Fe2+(5D) ions in zinc carbonates are explicitely calculated and then compared with experimental data obtained from the analysis of the Mössbauer magnetic hyperfine spectra of this system at liquid helium temperatures. It appears that at low temperatures this process also provides a competing mode for the exchange of energy between electronic spins and phonons.
The Dependence of Magnetic Ordering Temperature in Amorphous Semiconductors on Paramagnetic Centre Concentration
Authors: Khokhlov A. F. , Mashin A. I. , Satanin A. M. 
Published: July 2007

AbstractIn silicon amorphized by ion implantation (a‐Si) the dependence of magnetic ordering temperature (θ) on localized spin concentration (Ns) is studied by EPR method. Ns changes by varying the Ne+ ion dose from 6 × 1014 to 2 × 1017 cm−2 and sample annealing. From the comparison of the data obtained with literature ones conclusions are made about the existence of two critical values of Ns in a‐Si (≈ 1019 and ≈ 2 × 1020 cm−3), when a transition occurs from paramagnetism to antiferromagnetism (at T < θ) and from antiferromagnetism to ferromagnetism, respectively.
A Systematic Application of Gyarmati's Wave Theory of Thermodynamics to Thermal Waves in Solids
Authors: Fekete D. 
Published: July 2007

AbstractAn analysis is made of the approximate character of Fourier's heat conduction equation with respect to the theory of irreversible thermodynamics and with the various generalizations of the linear theory. The different explicit forms of the thermal wave equations in solids are deduced on the basis of the wave theory of thermodynamics developed by Gyarmati and the generalizations of the linear wave equations to quasilinear equations are treated. Finally, the derived equations are compared with the equations of the phonon dynamical theory and an analysis of the experimental situation is given.
Red Photoluminescence of α‐HgS Single Crystals
Authors: Soler G. A. , Aicardi J.‐P. , Leyris J.‐P. 
Published: July 2007

AbstractCathodoluminescence measurements on cinnabar (α‐HgS) published in a previous paper show that the emission peaked at 1.9 eV obeys a vibronic mechanism. The purpose of the present paper is to complete this characterisation by photoluminescence and excitation measurements (shape of spectrum, kinetics, thermal quenching). These different results allow to calculate the configurational coordinate diagram and to determine its location in the gap. It is also pointed out the influence of the traps and the non‐radiative centres revealed by measurements of photoconduction and thermal‐stimulated current.
Influence of Electron—Electron Scattering on Lorentz Number in Narrow‐Gap CdxHg1−xTe
Authors: Dubowski J. J. 
Published: July 2007

AbstractThe Lorentz number in CdxHg1−xTe (0.045 ≦ x ≦ 0.33) in the temperature range from 30 to 300 K is investigated experimentally and theoretically. Samples with an electron concentration of 1017 cm−3 ≦ n ≦ 1018 cm−3 are used. The experimental data compared to theoretical calculations show that e—e interaction plays an important role in samples with n ≦ 2.5 × 1017 and for x ≦ 0.15 at temperatures higher than about 30 K. For samples with higher electron concentration this mechanism becomes completely negligible.
Interband Magnetooptical Studies on the Semimagnetic Semiconductor Hg1−xMnxSe
Authors: Dobbowolska M. , Dobrowolska M. , Ga R. R. , Mycielski A. 
Published: July 2007

AbstractInterband magnetooptical studies are performed on Hg1−xMnxSe alloys at temperatures from 10 to 40 K and compositions x up to 11.5%. The obtained spectra are analysed using the Pidgeon‐Brown model modified by exchange interaction. Band parameters, including exchange integrals, are determined by a fitting procedure of the interband transition energies.
Real and Apparent Photoconduction in Single Crystals of Methyltriphenylphosphonium (TCNQ)2−
Authors: Eley D. D. , Kinnear S. , Willis M. R. 
Published: July 2007

AbstractPhotocurrents in single crystals and compressed discs of methyltriphenylphosphonium (TCNQ)2− can be observed at low temperatures where the dark current is greatly reduced, or by the use of a chopped light source and a narrow band amplifier or oscilloscope display. By chopping at appropriate frequencies the true photocurrent can be observed and bolometric effects eliminated. The true photocurrent, which is ohmic and linear with light intensity, shows a threshold at (2.7 ± 0.1) μm. The carrier lifetime is 140 ms above and below the phase change at 310 K, but at the phase change more than one lifetime is observed due to trapping.
A New Interpretation of EXAFS Spectra in Real Space. I. General Formalism
Authors: Babanov Yu. A. , Vasin V. V. , Ageev A. L. , Ershov N. V. 
Published: July 2007

AbstractIt is shown that the problem of determining the function of radial atomic distribution around an absorbing atom by oscillations of the X‐ray absorption coefficient belongs to a family of incorrect problems. A regularization algorithm is proposed for the problem concerned. Computational schemes realized involving the use of computers are described. Some results of model calculations are given.