bluuebunny/crossref_metadata_2025 huggingface dataset:
IR Absorption and Raman Scattering Spectra in Mixed Cuprous Halides
Authors: Talwar D. N. , Vandevyver M. , Kunc K. , Zigone M.
Published: July 2007

Green's function theory for the low concentration of point defects is used to calculate the impurity induced ir absorption and Raman scattering spectra in mixed cuprous halides. The same perturbation parameters extracted from the impurity mode study provide reasonable correspondence to the Raman structure data in the band mode region recently observed by Murahashi et al. and Vardeny et al.
Propagation of Displacement Pulses in Harmonic Crystals
Authors: Czachor A. , Holas A.
Published: July 2007

The time evolution of the displacement field due to a localized initial pulse is calculated for a harmonic crystal. It is analyzed in detail for some simple phonon dispersion relations and for propagation in symmetric directions. The front of the pulse usually travels with sound velocity, except the case of a concave dispersion relation – the velocity is then different (higher). A “thought” experiment in which the dispersion relation may be determined from the analysis of the time profile of the arriving signal is considered.
Theory of the Static Atomic Displacements in Ordinary Metals with Isoelectronic Impurity Atoms
Authors: Zhernov A. P. , Mamedov T. A.
Published: July 2007

Using the many‐electron theory of metals an equation is obtained for the determination of the field of atomic displacements ζm for the case of an isoelectron impurity atom. Besides the force parameters of the first order, those of the second and the third orders are also explicitly regarded in relationship for the effective force Fm, determining the static distortions of the crystal lattice near the defect. The appropriate force parameters are found in an arbitrary order using the pseudopotential theory. Regarding those terms of Fm, proportional to the force parameters of the second and third order, is shown to significantly affect the ζm values for Rm ≫ a (a is the lattice parameter).
Investigation of the Dislocation Spin System in Silicon as Model of One‐Dimensional Spin Chains
Authors: Grazhulis V. A. , Kveder V. V. , Osipyan Yu. A.
Published: July 2007

Magnetic properties of the dislocation dangling bond (DDB) spin system in silicon crystals are investigated by means of the EPR technique at T = (1.3 to 150) K. Experimental results are obtained which enable one to develop a one‐dimensional model of the spin system according to which the DDB chains are unstable with respect to the pairing of the neighbouring bonds (S = 1/2) to form singlet pairs (S = 0) at T ≦ 50 K, and, apart from that, possess a softened phonon spectrum. It is shown that both these peculiarities in the DDB chain properties can give rise to strong anomalies in the behaviour of the DDB‐EPR spectrum.
Peculiarities of an Electromotive Force Arising in a Semiconductor in a Non‐Homogeneous Magnetic Field (I)
Authors: Gulamov Sh. A. , Katulevskii Yu. A. , Muminov R. A.
Published: July 2007

The possibility of arising of both, longitudinal and transverse electromotive forces (e. m. f.) in a semiconductor placed only into a non‐homogeneous magnetic field is shown firstly. The appearance of the e. m. f. is due to the interaction of the spin and orbital magnetic moments of current carriers with an external non‐homogeneous magnetic field. The spatial distribution of current carriers, that of the electric field, and the expressions for the longitudinal and transverse e. m. f. are found by using the magnetohydrodynamical approximation.
Electroreflectance of InN Semimetallic Thin Films
Authors: Tyagai† V. A. , Snitko O. V. , Evstigneev A. M. , Krasiko A. N.
Published: July 2007

Plasma electroreflectance spectra (1.2 to 2.2 eV) and the bias dependence of capacitance are presented for InN semimetallic (N ≈ 3 × 1020 cm−3) thin films. The interference patterns in the electroreflectance spectra are analysed and grouped into two types according to the form of the electroreflectance undulations. From capacitance measurements the Fermi energy is determined to EF = (0.4 ± 0.1) eV. The contribution of Friedel oscillations to the capacitance is also discussed.
Impurity Photoconductivity of γ‐Irradiated LiF
Authors: Lee R. S. , Merklin J. F. , Marrs C. D. , Richter M. H.
Published: July 2007

The photoconductivity and absorbance of three batches of γ‐irradiated LiF crystals with different impurity levels are measured. Impurity levels are determined by neutron activation analysis. In absorbance experiments using polarized light, dichroism with 〈110〉 symmetry is observed in the region of a shoulder on the low‐energy side of the F band. The shoulder occurs in the spectral region where a photoconductivity peak is observed. It is shown that the same defect center produces the shoulder and the photocurrent peak. The data indicate that the center responsible for the photoconductivity is the Fz1 center.
Negative Magnetoresistance in Zinc Selenide
Authors: Ivanova G. N. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

The 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

On 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

Strong 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

Calculations 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

The 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

In 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

The 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

The 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

Various 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

The 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

The 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

A 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

Using 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

The 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

The 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

From 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.
The Influence of Layer Crystal Plate Thickness on Structural Phase Transitions
Authors: Lukiyanets B. A. , Danilevich‐Tovstyuk K. K.
Published: July 2007

The renormalization of phonon modes by electron‐phonon interaction in a layered crystal of different thickness is considered. It is shown that with decreasing thickness the sample becomes less liable to structural instabilities.
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

Exact 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

The 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

Electrical 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

Keating'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

In 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

A 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

The 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

Results 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

For 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

In 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

An 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

Cathodoluminescence 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

The 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

Interband 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

Photocurrents 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

It 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.
Kinetics of Defect Accumulation and Recombination. I. General Formalism
Authors: Kuzovkov V. , Kotomin E.
Published: July 2007

A general theory of the kinetics of radiation‐induced defect accumulation and recombination in solids and liquids limited by spatial correlations of Frenkel defects is presented and developed. Kinetic equations are solved making use of the superposition approximation. For the first time a correlation of the similar defects is taken into account, which arises indirectly due to dissimilar defect recombination. A radiation‐induced accumulation of immobile defects proves clearly a formation of loose aggregates of the similar defects. It is shown that a defect concentration grows with time t proportionally to 1 — exp (‐2μ0vat), μμ0 is the rate of defect production per unit volume and time, va being an annihilation volume. The less the initial defect correlation is in genetic (Frenkel) pairs, the greater is the defect concentration under saturation at high doses.
Sound Interactions with Nuclear Subsystem in Antiferromagnets
Authors: Chepurnykh G. K. , Tarasenko S. V.
Published: July 2007

A dispersion relation is obtained and studied. It follows from the relation that at low temperatures in the flop‐field region the studies of effects due to a coupling between electron and nuclear spin vibrations as well as effects due to a strong coupling between electrons and lattice vibrations substantially depend on the fact whether one takes or does not take into account sound interactions with the nuclear spin subsystem. The influence is shown of anisotropy of the relativistic part of magnetostriction on the character of the orientational phase transformations and the value of the NMR amplification coefficient.
Intrinsic Urbach Rule and Electron—Phonon Interaction in GaAs and Related III‐V Compounds
Authors: Antonioli G. , Bianchi D. , Franzosi P.
Published: July 2007

The optical absorption at the edge of the fundamental absorption band is investigated in highpurity and high‐perfection GaAs crystals. The experimental curves show an exponential decay of the absorption coefficient as a function of the photon energy (Urbach's rule) with temperature dependent slope. Since the impurity contribution can be neglected, the data are analyzed within the framework of the polaron model of phonon‐assisted transitions. The good agreement obtained between experimental and calculated curves makes it possible to conclude that the interaction of electrons with LO phonons plays a dominant role in shaping the intrinsic Urbach tail in GaAs. The same theoretical model is also applied successfully to InP and InAs using previously published experimental data.
Calculation of Structural Parmeters of Spinels
Authors: Talanov V. M.
Published: July 2007

A simple thermodynamical theory of crystal structure parameter calculation is suggested. Within the approximation of elastic atomic interaction formulae are obtained of the lattice parameter for different variants of cation distributions among non‐equivalent crystallographic positions in chemical compounds with spinel structure. The lattice parameter proved to be a function of two fundamental atomic characteristics: charge and bond length with an anion. The experimental and theoretical values are in good agreement. Calculation are made with sulfospinels.
The Local Density of States of Embedded Cu and Cu(Ni) Clusters
Authors: Van Dijkum C. E. , Lodder A.
Published: July 2007

The electronic structure of Cu and Cu(Ni) clusters is investigated being representative of the pure Cu and dilute Cu(Ni) alloy systems in a liquid or amorphous state. The clusters contain up to 43 atoms. The copper environment of the clusters is simulated by two kinds of embedding media, the John‐Keller medium and the Lenk‐Blaudeck medium. The local density of states (LDOS) for each atom in the cluster is evaluated using the formalism of Lloyd as well as of Anderson and McMillan. Calculations show that the Anderson‐McMillan LDOS, which follow from a local integration of the Green function, is preferable.
Self‐Diffusion of Iron in the Amorphous Alloys Fe40Ni40P14B6 and Fe80B20
Authors: Valenta P. , Maier K. , Kronmüller H. , Freitag K.
Published: July 2007

In amorphous and cystallized Fe40Ni40P14B6 and amorphous Fe80B20 alloys the diffusion coefficient of iron is investigated using radiotracers and a microsectioning technique. The diffusion coefficient in Fe40Ni40P14B6 can be described by an Arrhenius relation according to D equals; D0 exp (−Q/kT) with D0 equals; 10 cm2/s, and Q equals; 2.0 eV. In Fe80B20 no diffusion could be observed.
Raman Spectra of CaAs3, ús3, SrAs3, BaAs3, and α‐EuP3 and the Mixed Phases, Eu1−xSrxAs3, and Eu(P1−x Asx)3
Authors: Oleś B. , Stolz H. J. , Von Schnering H. G.
Published: July 2007

The Raman spectra of the triarsenides MAs3 (M equals; Ca, Eu, Sr, Ba), α‐EuP3 and of solid solutions, Eu1−xSrxAs3, and Eu(P1−x Asx)3, are measured. A great similarity between the phonon spectra and simple scaling relations between the corresponding lattice vibrations of the triarsenides reflect the strong structural relationships between the monoclinic MAs3 and slightly distorted triclinic CaAs3 and suggest very similar vibrational eigenvectors. The Raman spectra of the solid solutions, Eu1−xSrxAs3, and Eu(P1−x Asx)3, display a mixed one‐ and two‐mode behaviour. It is shown that the strong coupling between atoms in the puckered As(P) layers reflects itself in the appearance of high‐frequency modes associated mainly with vibrations of atoms within the puckered layer, whereas the low‐frequency modes are dominated by metal vibrations.
Infrared Absorption by Ag, Cu, and Au Acceptors in ZnTe
Authors: Samindayar K. , Magnea N. , Pautrat J. L. , Pajot B.
Published: July 2007

Infrared measurements are made on ZnTe doped with Ag, Cu, and Au acceptor impurities. Observed transitions are discussed in the framework of the theory of Baldereschi. The binding energies Ea are (123.8 ± 0.5), (150.3 ± 0.5), and (271.6 ± 0.5) meV for Ag, Cu, and Au impurity, respectively, These results are in good agreement with that deduced from luminescence experiments. The average number of emitted phonons N̄ is deduced for all known acceptors in ZnTe (Li, P, As, Ag, Cu, and Au) using luminescence and IR measurements. An empirical relation N̄ equals; 62E2a is found. The cross‐section for Au in ZnTe is found to be (3.5 ± 0.7) × 10−16 cm2 with an effective field ratio which ranges between 2.3 and 4.
Very Large Phonon‐Drag Thermoelectric Power of HgTe in Strong Magnetic Fields
Authors: Takita K. , Landwehr G.
Published: July 2007

The magneto‐Seebeck effect of almost intrinsic HgTe is investigated up to 96 kOe in the temperature range 20 to 120 K. The thermoelectric power in strong transverse magnetic fields. α⟂, is positive because the contribution of high mobility electrons is suppressed. Below about 50 K, α⟂ at 96 kOe increases rapidly with decreasing temperature and shows a prominent peak. The peak value of α⟂ of a typical sample reaches about 2 mV/K around 25 K. The dominant part of the observed value comes from the phonon‐drag effect of holes with large effective mass. The observed phonon‐drag contribution is one order of magnitude larger than that of heavily doped p‐type samples which were investigated previously. Such a large value is attributed to a substantially reduced hole—phonon scattering in the phonon relaxation mechanism of the almost intrinsic sample. According to an analysis using a model of phonon relaxation through three‐phonon processes discussed by Whitsett and Nelson, the dilation deformation potential constant of the Γ8‐band is determined as a equals; +3.8 eV using a shear deformation potential constant of b equals; −1.5 eV.
Assignment of (Tl+)2 Absorption Bands in Alkali Halides by Magnetic Circular Dichroism Spectra
Authors: Tsuboi T.
Published: July 2007

Magnetic circular dichroism spectra of absorption bands due to a Tl+ dimer center, i.e. (Tl+)2, in KI single crystals are investigated at temperatures from 25 to 300 K, which are compared with the spectra of (Tl+)2 bands in KBr and of (In+)2 bands in KCl. The absorption bands at 4.915 and 4.968 eV in KI:Tl+, which appear near the B‐band of Tl+ center, are attributed to the (Tl+)2 bands related to the B‐ and C‐bands, respectively.
Theory of Multiphonon Resonance Raman Scattering as a Function of Temperature in Polar Semiconductors
Authors: Trallero Giner C. , Lang I. G. , Pavlov S. T.
Published: July 2007

A theory is developed which describes multiphonon resonance Raman scattering processes in polar semiconductors when the temperature is not very high and the primary radiation frequency is in the fundamental absorption region. A general formula for the scattering cross‐section for any Stokes or anti‐Stokes process is presented as a function of impinging radiation frequency and temperature in the event of excitonic state interaction with longitudinal polarization lattice vibrations (LO‐phonons) considered as intermediate states. It is shown that the multiphonon resonance Raman scattering cross‐section in any process is proportional, in the first order, to the exciton‐LO‐phonon interaction constant.
Role of Noble Metal d‐States in the Formation of the Electron Structure of Ternary Sulphides
Authors: Domashevskaya E. P. , Marshakova L. N. , Terekhov V. A. , Lukin A. N. , Ugai Ya. A. , Nefedov V. I. , Salyn Ya. V.
Published: July 2007

Combined X‐ray spectroscopic and X‐ray photoelectron investigations are made of the valence electron energy spectra in the semiconducting ternary sulphides CuGaS2, AgGaS2, AgSbS2, Ag3AsS3, and CuFeS2. The main features of such spectra in the complex compounds of noble metals are shown to be governed by the resonance character of the interaction between the d‐states of noble metal and p(s)‐states of non‐metal as already observed earlier especially in binary compounds of noble metals. Its pecularities are manifesting themselves first of all by the splitting of sulphur p‐band into two components and by pushing the latter apart from the noble metal d‐band. The magnitude of this p‐band splitting increases almost linearly with the amount of copper or silver in the compound. With the use of these data for the first time the broadeningof band gap in AIBIIICVI2 ternary sulphides is explained, which occurs under substitution of copper by silver, contrary to the usual narrowing of it with the increase of the mean atomic number of a compound.
Problems of the OPW Method III. Rare Earths
Authors: Kurganskii S. I. , Farberovich O. V.
Published: July 2007

The application of the modified OPW method for calculating the band structure of rare earths is considered. The effect of the parameters of the MOPW method on the energy bands obtained is systematically studied for Eu and general rules on the choice of these parameters are found. The spin‐polarized band structure of the ferromagnetic semiconductor EuO is determined taking into account these rules. The effect of f‐states of the metal and the (m‐t) approximation of the crystal potential on the compound energy bands is studied.
Localized Positronium‐Like States in Ionic Crystals
Authors: Boev O. V. , Arefiev K. P.
Published: July 2007

The localized positronium‐like states in ionic crystals are considered as positron‐electron pair bound states in the Coulomb field of the charge Z. The system characteristics are evaluated as a function of the magnitude Z. The calculated data are in agreement with the experimental ones in alkali halides for charges Z < 0.7. The properties and the formation possibility of the positronium‐like states in ionic crystals are discussed.
Diamagnetic Band Structure Comparison of Second‐Order Perturbation with a First‐Principles Calculation
Authors: Rauh A. , Schellnhuber H. J.
Published: July 2007

The comparison is restricted to the Landau region where the periodic potential can be treated as a perturbation. The first‐principles calculation is done within a recently developed variational formalism. A two‐dimensional model potential is supposed and rational magnetic fields. For all Landau levels considered a striking agreement is found between the two energy spectra which are obtained by the perturbative and the variational method, respectively. The second‐order perturbation yields also the magnetic breakdown condition with high accuracy.
Electron‐Spin Polarization in Hexagonal Crystals Induced by Circularly Polarized Light
Authors: Wöhlecke M. , Borstel G.
Published: July 2007

From symmetry arguments general wave functions generating the irreducible representations of the double group of C6v are derived. From these wave functions selection rules for the production of spin polarized electrons along Δ in unpolarized hexagonal crystals by circularly polarized light are derived. Equal strength for spin‐up and spin‐down electrons produced by a particular transition is predicted, if right circular polarization is changed to left circular polarization. The absolute strength depends on a parameter proportional to the spatial parts of the wave functions. Very general conclusions on the effect of hybridization can be drawn.
On the Luminescence of Cs3Bi2Br9 Single Crystals
Authors: Timmermans C. W. M. , Blasse G.
Published: July 2007

The luminescence properties of Cs3Bi2Br9 single crystals are reported. Cs3Bi2Br9 is an ordered perovskite, structurally and electronically related to the cesium lead halides. Emission and excitation spectra are measured at 4.2 K. The luminescence originates from the recombination of excitons bound to defects, except for a sharp line at 459.2 nm, which is ascribed to free exciton recombination. The band‐gap transition takes place at about 2.7 eV and is found to be direct and allowed. The intensity of the emission bands and the decay times are measured as a function of temperature. The results are interpreted assuming detrapping and exciton migration.
Infrared Spectra of Single‐Crystal NiO at High Temperatures
Authors: Mochizuki S. , Satoh M.
Published: July 2007

The reststrahlen spectra of single‐crystal NiO are measured at various temperatures from 300 to 1273 K in the spectral region from 250 to 700 cm−1 by the thermal‐emission and reflection method for the first time. Remarkable changes are observed in the reststrahlen band with increasing temperatures. The spectra are analysed by means of the two‐oscillator dispersion model, and the temperature dependence of the dispersion parameters is determined. These results are discussed in the light of the theory on anharmonic crystals. The anharmonic phonon‐frequency shift is seen to become prominent with increasing temperatures. Appearance of the high‐frequency sideband is ascribed to a process involving multi‐phonons through the intermediate virtual excitation of the TO‐phonon near the center of the Brillouin zone.
Zeeman Effect in Low‐Temperature Luminescence Spectra of Molecular Ions O−2 and S−2 in Alkali Halide Crystals
Authors: Sild O. , Sildos I.
Published: July 2007

The effect of the magnetic field up to 3.5 T is investigated on the zero‐phonon luminescence lines of the molecular ions O−2 and S−2 in alkali halide crystals at 4.2 K. For the molecules oriented along the twofold axis of the cubic crystal a triplet splitting of the luminescence lines is observed. A model for the selection rules and the polarization characteristic of the Zeeman triplets is developed. The parameters of the excited electronic state can be obtained from the Zeeman triplets.
The Role of Defects on Inelastic Scattering of Mössbauer Radiation near Structural Phase Transitions
Authors: Zolotoyabko E. V. , Kashcheev V. N.
Published: July 2007

An expression for the spectrum of critical inelastic scattering of Mössbauer radiation is derived at the structural phase transition. It is assumed that the central peak (which determines such characteristics of scattered radiation as the intensity and the width) is due to slow motions of point defects. The temperature dependence of the effective line width is found to arise from vacancy diffusion in BaTiO3 to the right of the transition temperature. Qualitative agreement with corresponding experimental data is obtained.
Excitation of the hybrid mode due to modulation of an intense laser beam in a transversely magnetised semiconductor plasma
Authors: Ghosh S. , Apte N. , Agarwal V. K.
Published: July 2007

Using the hydrodynamic model of a homogeneous plasma, the modulational decay of a laser beam into an acoustic wave and another electromagnetic wave is studied in heavily doped n‐type semiconductors in the presence of a transverse magnetic field. The decay process results in the excitation of the hybrid mode. The growth rate and the threshold electric field necessary for the onset of instability is obtained in presence as well as in absence of the magnetic field. The magnetic field couples the acoustic wave and the electromagnetic waves. The growth rate of the unstable hybrid mode increases with the square of the amplitude of the magnetic field.
Photolumineseenee of ZnO single crystals: Influence of k‐linear interaction and non‐analytic long‐range exchange on the emission spectrum of the free A‐exciton
Authors: Kuhnert R. , Helbig R. , Hümmer K.
Published: July 2007

The effect of the non‐analytic long‐range exchange interaction as well as the k‐linear interaction on the photoluminescence spectrum of the free A‐exciton in ZnO is investigated. By varying the angle between wave vector and crystallographic c‐axis in uniaxial crystals one is able to “switch on and off” and to vary the coupling strength of these interactions. In order to avoid refraction complications connected with non‐perpendicular incidence the measurements are carried out at crystal planes inclined under different angles to the crystallographic c‐axis. This method enables to observe and to study systematically the influence of k‐linear terms and non‐analytic long‐range exchange on the emission spectrum for the first time without an external field.
Absorption spectra of MgF2 and AlF3, in the region of the Mg and Al L2,3 excitations
Authors: Bartlett R. J. , Olson C. G. , Lynch D. W.
Published: July 2007

The absorption spectra of thin films of MgF2 and AlF2 were measured in the region of the Mg and Al L2,3 excitations using synchrotron radiation. The spectrum for MgF2 is similar to that previously reported, but with two differences. The lowest energy (exciton) structure is resolved into two peaks leading to new values of the spin‐orbit and exchange splitting, 0.33 and 0.21 eV, respectively, and there are a number of peaks in the original spectrum that were not obtained. The AlF3 spectrum shows that these arose from AlF3, contamination of the original films. The AlF3 spectrum bears a striking resemblance to that of MgF2, indicating that critical point structures probably play no role. Structure in the first exciton peak is not resolved in the absorption spectrum but thermotransmission spectra reveal a splitting of 0.44 eV.
Determination of static bond charge properties in Ga1−xInxAs and GaAs1−yPy, solid solutions
Authors: Pietsch U.
Published: July 2007

The integrated X‐ray intensity is determined for some monocrystalline reflections of (GaIn)As and Ga(AsP) layers, grown on GaAs substrates, nearly of those compositions where the scattering amplitude of the spherical atoms vanishes. These reflections are particularly apt to inform about the charge heaping up between next neighbours. By means of a bond charge model the experimental values are interpreted. Besides, data are obtained for the mean square displacement of the matrix atoms in the mixed crystal. The mean square displacements of the atoms in the mixed crystals cannot be extrapolated from those of the end components. The atoms of the substitutional sublattice oscillate less intensively than in its binary compounds. The bond charge, however, changes nearly linearly between the end components.