bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended Model of Bond Charges and Its Application in Calculation of Optical Properties of Crystals with Different Types of Chemical Bonds
Authors: Tsirelson V. G. , Korolkova O. V. , Rez I. S. , Ozerov R. P.
Published: July 2007

A method for calculating the optical characteristics of crystals with different types of chemical bonds within the framework of the dielectric theory of chemical bond put forward by Philips and Van Vechten is suggested. The calculating scheme which does not contain adjustable parameters is based on the bond charge model designed by Levine, which is generalized for the case of multiple bonds and modified involving the density functional method data on the spatial distribution of electrons in atoms. The structural elements of the method are: the screened Coulomb potentials and radii of the atomic core, bond lengths and charges, and the distances from the nuclei to the centres of gravity of the latter. The calculated characteristics of the crystals (dielectric permittivity, quadratic and cubic non‐linear susceptibilities, electrooptical constants) are in good accordance with experimental findings. An attempt is made to predict the non‐linear optical characteristics according to precision X‐ray diffraction data on the electron structure of its only representative, lithium formate deuterate LiHCO2 · D2O, whereby a fairly good fit with the experimental data is achieved.
K‐Absorption Spectra of Copper Oxides
Authors: Aggarwal O. P. , Saxena N. N.
Published: July 2007

The extended fine structure of K‐absorption edge of copper in its oxides is studied using a 40 cm curved crystal spectrograph. The observed shift of K‐edges of copper in the oxides is better explained with MO and SRO theories. Separations apparent between the absorption minima corresponding to copper and oxygen atoms in the lattices of two oxides support the MO viewpoints.
Quantum‐Theoretical Model of Adiabatic Rate Processes in Condensed Systems or at Interfaces
Authors: Lorenz W. , Engler C.
Published: July 2007

A quantum‐theoretical model of rate processes in condensed systems is developed which is capable of treating partial charge transfer phenomena and chemical bond formation. Adiabatic local potential surfaces of a reactive subsystem are subjected to a unitary transformation into species potential surfaces; the phonon‐assisted conversion of chemical species can then be calculated in the common T‐matrix framework. In numerical calculations, anharmonicity of species potential surfaces and dependences of the electronic transition element upon nuclear coordinates is allowed for. As specific application, photoelectrochemical processes on semiconductor surfaces with fractional electrons or holes are considered.
Stimulated Brillouin Scattering of Laser‐Radiation by an Electron‐Acoustic Wave in Magnetised Semiconductor‐Plasmas
Authors: Guha S. , Basu C.
Published: July 2007

Using the hydrodynamic model of a plasma, the stimulated Brillouin scattering of laser radiation by an electron‐acoustic wave is investigated analytically in a semiconductor plasma in the presence of a dc magnetic field including the effect of the ponderomotive force. It is shown that the magnetic field decreases the threshold electric field and the growth rate.
Theory of Second‐Order Auger Recombination in Strong Degenerate Small‐Gap Semiconductors Application to PbSSe
Authors: Beiler Marion , Mocker M. , Ziep O.
Published: July 2007

A theory to estimate the efficiency of second‐order Auger processes in strongly degenerate systems (T → 0 K) is developed, whereby a parabolic isotropic band structure model is adapted to PbS0.1Se0.9. The calculation of the net recombination rate refers to a range of doping and excitation concentration where first‐order Auger processes are strongly reduced or, in the zero temperature limit, are even forbidden. The numerically calculated small‐signal lifetime for a semiconductor with the doping concentration ND = 1017 cm−3 has the order of magnitude ≈ 10−6 s.
The Auger Processes with Energy Transfer to the Bound Charge Carriers in Multi‐Valley Semiconductors
Authors: Vorobev Yu. V. , Tolpygo E. I. , Sheinkman M. K.
Published: July 2007

The theory of the Auger processes of capture of charge carriers with the energy transfer to the bound charge carriers is extended to the case of a semiconductor with different valleys of the C‐band. Using hydrogen‐like Ψ‐functions for the charge carriers in the impurity centres separated with distances higher than the sum of the effective radii of the interacting states, expressions are obtained describing the dependences of the cross‐sections on the characteristic parameters for the four types of Auger processes: hole capture by the “donor—donor” complex, and the capture of the electron from the upper valley by the complexes “donor—donor”, “donor—acceptor”, “acceptor—acceptor”. It is shown that in many cases the cross‐section of the process examined can surpass the effective size of the bound electron state and reach a value ≈ 10−12 cm2. On the basis of the data obtained an interpretation is given of a number of experimental facts connecting the effects of capture and ionization in GaAs doped with deep‐level impurities (O, Fe, Cr) and InP:Fe.
Impurity Conduction along the Least Resistance Paths of Granular Insulating Thin Films
Authors: Barrière A. S. , Gevers G.
Published: July 2007

The electrical charge transfer is investigated through Au—FeF3—Au thin‐film structures as a function of the crystallization degree of the insulating layers. For a constant growth rate, the texture of the samples, prepared by sublimation under vacuum, depends essentially on the substrate temperature during the condensation of the vapours (Ts). Between 450 and 650 K, the FeF3 thin films are granular. The crystallized grains, the average diameter of which increases with Ts, are embedded in a disordered matter. Under these conditions, the dc conductivity of the structure greatly depends on the preparation parameter Ts. However, in all cases, as for many other insulators, the charge transfer throughout FeF3 is due to the presence of localized electronic states situated into its band gap. These states correspond to a weak lack of fluorine and are situated at 1.1 eV below the conduction energy. Now it is demonstrated that the corresponding Coulombic wells in interaction are more particularly concentrated in the intergranular zones of the layers. If their density remains constant in the whole, it grows with Ts in these regions when the volume of disordered matter decreases, which defines the least resistance paths. Along these percolation ways, the average height of the potential barriers separating two consecutive states decreases when Ts increases. In consequence, if the dc conductivity results from thermally activated jumps of electrons above these potential barriers at high temperature, below a temperature which increases with Ts a hopping process predominates.
Electron Transfer and Thermal Vibration Parameters in Titanium Nitride: An X‐Ray Diffraction Study
Authors: Field D. W.
Published: July 2007

An X‐ray diffraction study of titanium nitride powder of composition TiN0.89 is carried out at room temperature. The electron transfer from the Ti atom to the non‐metal sites is found to be (1.5 ± 0.3) electronic charges. The values of the r.m.s. vibration amplitudes of the atoms are uTi = (7.12 ± 0.04) pm, uN = (6.1 ± 0.3) pm, and the Debye temperature is (580 ± 20) K.
The Distribution of Magnetic Moments and the Temperature Dependence of Reduced Hyperfine Fields in Amorphous Ferromagnets
Authors: Kaneyoshi T. , Tamura I.
Published: July 2007

The distribution of magnetic moments in amorphous transition metal—metalloid ferromagnetic alloys is first estimated from the linewidths of hyperfine fields. The result shows that there exists a rather broad distribution of magnetic moments with some spins aligned antiferromagnetically in the alloys. The temperature dependence of reduced hyperfine fields in the alloys is evaluated by a simple molecular‐field theory, taking account of the distribution of magnetic moments in addition to the usual exchange fluctuations. Quantitative agreement between the theoretical and experimental curves is more rectified at the intermediate reduced temperature range, in comparison with the case of the usual exchange fluctuations.
Transient Coherent Anti‐Stokes Raman Spectroscopy of Surface Polaritons
Authors: Likholit N. I. , Ponath H.‐E. , Strizhevskii V. L. , Yashkir Yu. N.
Published: July 2007

A theory of the coherent anti‐Stokes Raman spectroscopy (CARS) of surface polaritons (SP) is developed. General expressions for the intensities of ultrashort SP pulses excited by the biharmonic pump pulses and expressions for the CARS signal intensity are obtained. The specific features of the SP pulse generation and scattering are analysed.
The Theory of Double Gamma Resonance in Paramagnetics
Authors: Sadykov E. K.
Published: July 2007

The theory of double γ‐resonance for a paramagnetic system is suggested. The electron—nuclear (EN) state representation is used which allows to descibe the cases where the effective field approximation is not correct. The theory enables one to calculate the quasienergetic structure of the γ‐resonance spectra at the conditions of radiofrequency (rf) excitation at the frequencies of the nuclear magnetic resonance (NR) and the electron magnetic resonance (EPR) from a single point of view. The method allows also to describe consistently DGR spectra in the limit of slow electron relaxation (ER) and in the frame of a stochastic model for arbitrary relaxation rate.
Exact Density Functionals for Ground‐State Energies. I. General Results
Authors: Englisch H. , Englisch R.
Published: July 2007

The exact one‐particle density functionals by Levy and Lieb for the calculation of ground‐state energies are analysed. A method for the calculation of the Levy‐Lieb functional is proposed. Based on a work by Lieb, the range of validity of the exact self‐consistent equations by Kohn and Sham is determined. A self‐consistent procedure which is applicable in a wider range is presented.
Effect of Supercurrent on Charge Imbalance Relaxation in a Phase Slip Centre
Authors: Chashoo G. J. , Singh Y.
Published: July 2007

The quasiparticle charge imbalance relaxation time in the nonequilibrium state of a phase slip centre in indium whiskers is calculated taking into account the depairing effect due to supercurrent and the finite size of the core. The normal‐like length for the first phase slip centre for various temperatures below the transition temperature is calculated and compared with the experimental data. The analysis shows that the core of phase slip centre is about four times the Ginzburg‐Landau coherence length. This result is new. Further the effect of pair breaking due to supercurrent on the charge imbalance relaxation time for various values of τE is calculated for temperatures 1 to 50 mK away from the transition temperature.
Electrical Resistivity Calculations for Amorphous CuxAl1−x
Authors: Knuyt G.
Published: July 2007

The electrical resistivity ϱ and its temperature coefficient α are calculated for different compositions of the CuxAl1−x amorphous alloy using a pseudopotential theory. The calculated resistivity ϱ(x) agrees well with the experimental data when hybridization effects for copper are included. Different pseudopotentials are tested on their validity. The calculated α(x) curve does not reproduce the experimental CuxAl1−x data accurately, but has characteristics found in other experimental data. Finally a mechanism is suggested which can be responsible for the resistivity minimum at low temperatures for amorphous alloys in certain cases.
Time‐Dependent Ginzburg‐Landau Equations for Anisotropic Superconducting Alloys
Authors: Vones G. , Schachinger E.
Published: July 2007

In the framework of space and time dependent Green's functions an implicite expression for the energy integrated electron Green function is presented for anisotropic superconducting alloys. Normal and paramagnetic impurity scattering is included as well as relaxation processes due to inelastic electron scattering. The theory is later on specialized for an anisotropic system with normal momentum scattering only in order to study the ‘smearing’ out of the anisotropy. A separable model is finally employed to describe the anisotropy of the Fermi velocity and of the electron—phonon interaction. Within this model the influence is studied of the mean square anisotropy and of the normal impurity concentration on the Ginzburg‐Landau parameter, on the critical temperature, on the upper critical magnetic field, and on the penetration velocity of the flux vortices.
Fluctuations in a Nonequilibrium System of Electrons and Magnons in Ferromagnetic Semiconductors
Authors: Ya. Korenblit I. , Tankhilevich B. G.
Published: July 2007

The fluctuations in the electron and magnon systems of a ferromagnetic semiconductor in strong electric fields are investigated. The expressions for the correlation functions of the magnon temperature and the longitudinalmagnetic moment fluctuations are derived. The magnon noise temperature is obtained and it is shown that it may exceed the magnon temperature.
On the Theory of Solitary Wave Excitation in Molecular Crystals by a Coherent Electromagnetic Field
Authors: Kruglov V. I.
Published: July 2007

A closed integro‐differential equation is obtained which describes solitary wave propagation in a molecular crystal. It is shown that from this equation a system of differential equations for the module of the exciton amplitude and the slow part of phase follows, as well as the dispersionrelation. On the basis of the method proposed for solving nonlinear equations two types of solitary waves are found, as well as a system of algebraic equations for defining the soliton parameters. All the results are obtainedwithout using truncated equations and taking into account Pauli statistics for excitons.
Nonlinear Exciton Transmission in CdS Non‐Homogeneous and Non‐Stationary Model Calculations
Authors: Nguyen Hoang Xuan , Zimmermann R.
Published: July 2007

The transmission of a thin semiconductor platelet is studied by solving Maxwell's equation together with a rate equation for the exciton concentration. The concentration induced exciton broadening serves as nonlinear mechanism. Numerical results for the diffusion‐controlled concentration profile in the sample are presented. As a second case, the temporal transmission lineshape of a Gaussian input pulse is calculated and compared with our experimental results on CdS. The hysteresis phenomenon found is interpreted in terms of a transient effect.
Dispersion and Absorption Anomalies in Three‐Level Systems
Authors: Hönerlage B. , Bigot J. Y.
Published: July 2007

Using the density‐matrix formalism, the dielectric function of athree‐level system under high excitation conditions is determined. The density matrix being calculated by a continuous matrix inversion, non‐resonant contributions and saturation effects can be fully accounted for and the stability of absorption and dispersion anomalies may be discussed.
Infrared Reflectivity Plasma Spectra of TlBiTe2 Single Crystals
Authors: Paraskevopoulos K. M. , Siapkas D. , Economou N. A.
Published: July 2007

Infrared reflectivity plasma measurements performed in the range 300 to 4000 cm−1 on TlBiTe2 single crystals with a high density of coherent and semicoherent twins, at room temperature, reveal a frequency relaxation time of the form τ−1(ω)  τ0−1 + bωn. With n = 2.35 satisfactory fits to the experimental plasma reflectivity data are obtained incorporating the above expression for τ(ω) in the Drude model. Discrepancies between the classical theory and the experiment are attributed to the scattering of free electrons by twin boundaries.
Absorption and Magnetic Circular Dichroism Spectra of CsI:Tl+3
Authors: Stillman M. J. , Jacobs P. W. M. , Gannon K. Oyama , Simkin D. J.
Published: July 2007

The temperature dependence of the optical absorption and magnetic circular dichroism (MCD) of CsI crystals doped with Tl+ is measured between liquid helium temperature and room temperature. The absorption spectra are more complicated than usual for impurity ions with the s2 ground‐state configuration and show five strong bands on the long‐wavelength side of the absorption edge. Three of these bands are assigned to internal transitions of the Tl+ ion and the other two to charge‐transfer transitions. The first and second moments of the first two absorption bands, as well as the first and third moments of thecorresponding MCD bands, are determined from spectra measured below 140 K. For these bands at higher temperatures and for the remaining bands strong overlapping precludes a meaningfull determination of the higher moments. Coupling constants and g‐values are obtained from the moments, and the origin of the spectral bands is discussed.
Correlation of Zero Field Splittings and Site Distortions Interstitial Incorporation of Mn2+ in Urea‐Ammoniumchloride (H2N)2CO · NH4Cl
Authors: Heming M. , Lehmann G.
Published: July 2007

In (H2N)2CO · NH4Cl single crystals doped with Mn2+ three crystallographically inequivalent sets of EPR spectra with relative intensities of 8:3:2 are observed and analyzed. The second order zero field splitting parameters b02 = ‐744.7; ‐712.2; ‐736.5 and b22 = ‐127.1; ‐160.8; ‐111.2 (all in 10−4 cm−1) and the directions of their principal axes can only be explained by incorporation of Mn2+ into interstitial sites midway between two NH4 sites with two water molecules replacing these ammonium ions in close analogy to NH4Cl:Mn.
Investigation of the Weak‐Field Charge Transport in Semiconducting V2—VI3 Compounds with Trigonal Symmetry I. Expanded Model for the Transport Coefficients
Authors: Stordeur M.
Published: July 2007

In the series of trigonal V2—VI3 semiconductorsBi2Te3, Bi2Se3, and Sb2Te3 up to now it has not been succeeded to interpret the temperature dependence of the weak—field charge transport for Sb2Te3 single crystals in terms of a physical relevant model with reasonable semiconductor data. Therefore, an expanded transport model is presented takinginto account nonparabolic manyvalley band structure as well as the simultaneous action of anisotropic mixed charge carrier scattering by acoustical phonons and ionized impurities in the relaxation time approximation. Under these conditions the expressions for the thermoelectric, galvano‐ and thermomagnetic coefficients and the Lorenz numbers are given. These formulas are also valid for Bi2Te3 at pure acoustical mode scattering and for Bi2Se3 at single‐valley band structure.
Neutron Scattering Studies on Phase Transition and Phonon Dispersion in Cs2NaBiCl6
Authors: Prokert F. , Aleksandrov K. S.
Published: July 2007

The structural phase transition (PT) of elpasolite‐type crystal Cs2NaBiCl6 is investigated by neutron scattering. At first the acoustic phonon dispersion is measured at room temperature for the highsymmetric directions Δ, ∑, and Λ of the Brillouin zone. The transverse rotary mode is studied for phonon wave vectors q parallel as well as perpendicular to Δ and the dispersion shows a quasitwo‐dimensional behaviour of the Cl‐octahedra rotation. At cooling down to the PT, this branch shows a softening along Δ, reaching the lowest energies at the zone centre. The PT, which is found to be of weakly first order, seems to be driven and triggered by the ferrorotative octahedra mode.
Cluster‐Bethe‐Lattice Treatment of the Interstitial Boron Centre in Irradiated Gallium Arsenide
Authors: Kleinert P.
Published: July 2007

The radiation‐induced interstitial defect B(1) in GaAs is theoretically analysed by a cluster‐Bethe lattice treatment. Theoretical results obtained for a B—Ga dumbbell in gallium arsenide agree quite well with experimental data. The dumbbell coupling is about three times stiffer than the bonds between host‐lattice atoms. The separation of thedumbbell atoms amounts to one lattice constant. Due to the isotopy of gallium atoms all B(1) bands should exhibit a double‐peak structure with a small frequency split of about 1, 0.1, and 0.4 cm−1 for the A1, B1, and B2 modes, respectively. A resolution of these splittings would supply additional evidence for the B(1) defectmodel discussed here.
The Energy Band Structure of the Corundum (0001) Surface with Different Extent of Hydroxylation
Authors: Pushkarchuk A. L. , Mardilovich P. P. , Trokhimets A. I. , Zhidomirov G. M. , Gagarin S. G.
Published: July 2007

A theoretical study of the energy band structure is made for corundum (α‐Al2O3) (0001) surface within the frameworkof the crystalline orbital method. From the results, the dispersion dependences of the electronic energy in chosen directions of the surface Brillouinzone are obtained. For the Al atoms sp‐ and spd‐orbitals are considered to evaluate the effect of an appropriate basis on the results. The dependence of the energy band structure parameters on the extent of the surface hydroxylation is established. A comparison of the theoretical data with experimental ones is made.
A Theoretical Study of Simple Complexes of Point Defects in Alkali Halides by the Lattice Static Method
Authors: Augst G. R. , Vladislavskii Yu. I.
Published: July 2007

Expressions are obtained for the energy of alkali halide crystals with two kinds of simple complexes of point defects – divalent impurity with vacancy and bivacancy – using the lattice static method. The heat of solution of Mg2+, Ca2+, Sr2+, and Ba2+ in NaCl, KCl, and KBr is calculated. Numerical calculations show that in some cases the nearest‐neighbour complex is less stable than the next‐nearest‐neighbour complex. The formation energy of a bivacancy is calculated in the same crystals. The results are consistent with those obtained experimentally. It is shown that in the latter case the configuration of the nearest‐neighbour complex is the most stable one.
Intraconduction Band Magneto‐Optical Study of InSb under Hydrostatic Pressure
Authors: Huant S. , Dmowski L. , Baj M. , Brunel L. C.
Published: July 2007

The cyclotron resonance and electron spin resonance of n‐InSb under hydrostatic pressure up to 1 GPa are investigated using photoconductivity techniques. All the transitions observed are fitted using a modified Pidgeon‐Brown model with a set of band parameters recently proposed by Goodwin and Seiler and a change of the band gap of dEg/dP = (0.140 ± 0.004) meV/MPa, a value in good agreement with experimental results.
Calculation of the Effect of Hydrostatic Pressure on the Band Structure of GaP and GaSb
Authors: Gorczyca Izabela
Published: July 2007

The band structure of GaP and GaSb is computed by the empirical pseudopotential method (EPM) including a nonlocal correction. The pressure dependence of the energy gaps and the wave functions are then calculated for these materials.
The Electronic Spectrum of the CrO Ion in the Ca2SiO4 · CaCl2 Host Lattice
Authors: Borromei R.
Published: July 2007

The polarised absorption spectrum of single crystals of Ca2SiO4 · CaCl2 containing chromium as CrO or CrO is measured at 4.2 K in the range 8000 to 46000 cm−1. By a careful analysis based on a Td → D2d site symmetry perturbation and on the band polarisation behaviour, it is concluded that the observed spectrum is due to CrO, the ground state is 2E and the system of bands in the region 10000 to 20000 cm−1 corresponds to the ligand field transition. Moreover all the observed bands except that at 37730 cm−1 correspond to a 2T2 excited state.
Charge Ordering in the Anti‐Th3P4 Structure
Authors: Lorenz B.
Published: July 2007

The existence of charge ordering in rare‐earth compounds crystallizing in the anti‐Th3P4 structure is investigated. On the basis of Madelung energy calculations it is shown that for instance in Eu4As3 the electrostatic interactions stabilize a charge ordered low temperature phase. The thermodynamics and the transition to the disordered phase are described by a lattice gas model. The transition is found to be of first order. The transition temperature estimated for Eu4As3 lies well above room temperature. The theoretical results are compatible with recent experiments, although the transition itself has to be confirmed by high temperature measurements.
Low‐Temperature Photoluminescence of the Aggregate Centres in Eu2+‐Doped KCl Crystals
Authors: Mugeński E. , Cywiński R.
Published: July 2007

The emission spectra and fluorescence lifetimes of different aggregation products of Eu2+ dipoles in KCl matrix are examined in the range 15 to 300 K. Two aggregation types are formed in dependence on the annealing temperature. The optical properties of the aggregates (i) and (ii) formed at RT and 125 °C are very similar to those characteristic of isolated dipoles. Above 125 °C both aggregates undergo decomposition. A third aggregation product is formed between 200 and 250 °C. Differently from (i) and (ii) the pertinent absorption and emission spectra do not show any vibronic structure. The effect of the above aggregation products on the fluorescence lifetime of isolated dipoles present in crystals is ascertained.
Absorption of Circularly Polarized Light by Solids
Authors: Jalbert Ginette , Brandi H. S.
Published: July 2007

The multiphoton absorption rate of circularly polarized light, by direct‐gap crystals, is investigated following a non‐perturbative scheme proposed by Jones and Reiss. It is possible to derive closed analytical solutions, for the N‐photon transition rate, valid for all field strengths of practical interest. The accuracy of the approximations introduced in deriving these results is determined comparing the numerical computations of the multiphoton transition rate (“exact”) with the analytical solutions. Specific calculations are done for ZnS and GaAs in the presence of a Nd laser. It is shown that this formalism leads to a total transition rate which has not the tunneling behavior previously discussed by several authors within similar contexts.
Excitonic Surface Polaritons in Luminescence from ZnTe Crystals
Authors: Brodin M. S. , Bandura V. M. , Matsko M. G.
Published: July 2007

The form and structure of reflection and exciton–polariton luminescence spectra of ZnTe crystals are studied in the region of the ground (n = 1) exciton state. The longitudinal–transverse splitting magnitude ΔELT is determined from the shape of the reflection spectra. A detected doublet structure of an emission band from the lower polariton branch is associated with the k‐linear term. The evolution of bulk and surface polariton luminescence spectra versus temperature and wave length of the exciting light is investigated.
Dynamical Behavior of the High Density Electron–Hole System in CdSe
Authors: Unuma Y. , Abe Y. , Masumoto Y. , Shionoya S.
Published: July 2007

Time changes of exciton reflection spectra in CdSe under high intensity excitation by picosecond pulses corresponding to band‐to‐band excitation are observed at 2 and 77 K, in order to obtain further information on the dynamical behavior of high density electron–hole plasma. It is found that just after picosecond excitation the exciton reflection structure disappears, but it recovers gradually with the lapse of time, and that the stronger the excitation intensity is, the longer the recovery time becomes. Comparing these results with time‐resolved luminescence spectra observed under the same excitation conditions, it is concluded that as time proceeds, the electron–hole plasma state is transformed to the high density exciton state, and that the luminescence in the late stage is due to the inelastic collision of excitons. It is sure that the formation of electron–hole liquid does not take place.
Pressure Dependence of the Melting Point of Al
Authors: Soma T. , Itoh T. , Kagaya H.‐Matsuo
Published: July 2007

The temperature dependence of the mean‐square displacement for Al is quantitatively calculated from first principles. The Debye temperature at higher and lower temperatures is also estimated using Debye's model. Then, using the volume dependence of the mean‐square displacement, the pressure effect on the melting temperature of Al is studied by Lindeman's melting law, and the melting curve obtained increases as function of the compressed volume.
Group Representation of the Formation Probabilities of Athermal Vacancy Clusters in Atomic Collision Cascades
Authors: Melker A. I. , Romanov S. N.
Published: July 2007

Athermal formation of vacancy clusters in displacement cascades is considered in the binary collision approximation. A diagram technique describing the process is suggested. On this basis the group representation of the formation process of vacancy cluster is constructed. The vacancy distribution in the clusters is found in good agreement with the computer simulation results for both f.c.c. and b.c.c. metals.
Comparison of an Extended Interstitial with a Split Interstitial in Silicon
Authors: Wesser K. , Sahu S. N. , Karins J. P. , Corbett J. W.
Published: July 2007

Molecular mechanics (MM) is a computer program used in organic chemistry to model the interactions of atoms in a molecule and thereby determine its configuration. The program models the interactions between atoms using two‐body potentials, bond‐bending and bond‐twisting force constants, and van der Waals interactions. In this paper MM is applied to silicon for the first time and used to study defect structures in crystalline silicon. In particular, the Jackson model and the <100> split interstitial are treated and configurations obtained. The resultant structures are then used for molecular orbital calculations using extended Hückel theory (EHT), to give oneelectron energy levels in the band gap. It is found that the Jackson interstitial has a high formation energy which does not favor this defect as a high temperature defect in silicon.
Divacancy in H.C.P. Metals
Authors: Monti A. M.
Published: July 2007

Static properties of divacancies at first, second, third, and fourth neighbours are investigated in a h.c.p. lattice by using computer simulation techniques. The calculations are performed with short range pair interatomic potentials fitted to some Mg properties. The formation, relaxation, and binding energies as well as the strength dipole tensor of the above defects are computed and the results compared with those of earlier authors. The corresponding formation and binding entropies are also calculated and the defect stability analysed. From the results, the instability of the third neighbour divacancy can be predicted.
Dispersion Relations for Magnon‐Polaritons in Uniaxial Ferrimagnetic Crystals
Authors: Merten L. , Kotzott R. , Lehmeyer A.
Published: July 2007

General dispersion relations are derived for the components of the permeability tensor and the refractive indices of uniaxial ferrimagnetic crystals making use of symmetry properties. The zeros of the polynomials in the dispersion relations can be interpreted as frequencies of special magnons and magnon‐polaritons. Some of these frequencies correspond to longitudinal magnons in the limit of large wave vectors.
On Phase Transitions in LiNH4SO4
Authors: Torgashev V. I. , Dvořák V. , Smutný F.
Published: July 2007

A Landau‐type thermodynamie theory describing the sequence of phase transitions in lithium ammonium sulphate at atmospheric pressure is developed. The form of the phase diagram is derived and compared with that constructed on the basis of published experimental data. The existence of a new monoclinic high pressure phase is proposed. Formulae for permittivity are presented and compared with available experimental data. Soft mode features of Raman and infra‐red spectra are briefly discussed.
Time‐Resolved Reflectivity Measurements on RF Sputtered a‐Si:H Alloy
Authors: Lue Juh Tzeng
Published: July 2007

Photoinduced carrier lifetimes of RF sputtered a‐Si:H alloy are measured by time‐resolved reflectivity and photoconductivity decay methods. Both experiments indicate a lifetime of about 5 μs. A calculation of the relaxation time of photogenerated carriers from extended mobility edge to midgap localized states satisfactorily agrees with this value.
Crystal‐Independent Interionic Potentials and the Lattice Dynamics of the Perovskite‐Type Layer Material K2ZnF4
Authors: Rauh H. , Geick R.
Published: July 2007

The phonon dispersion relations of K2ZnF4 are analyzed by lattice dynamical rigid ion and shell model calculations. It is shown that the concept of crystal‐independent interionic potentials is applicable for this non‐cubic substance. There is a structural unit in the tetragonal perovskitetype layer material K2ZnF4 in common with the cubic perovskite KZnF3, namely the ZnF6 octahedra. The influence of the crystalline environment on the lattice dynamical behaviour of this structural unit is studied by comparison of the phonon dispersion relations of both materials.
Self‐Consistent Dynamical Theory for Heisenberg Spin Glasses
Authors: Schreiber J. , Schulz D.
Published: July 2007

A sel‐consistent RPA theory is constructed to describe a spin glass (SG) state in the Heisenberg model (S = 1/2). The investigations are based on the assumption of a collinear spin structure and of strong quantum fluctuations: 〈S〉 ≪ 1/2 (quantum spin glass QSG). In the lowest order the structural fluctuations are expressed by the fluctuations of the molecular fields Hi, for which the probability distribution is self‐consistently determined by a Lorentzian one with a temperature dependent width Γ(T). This quantity plays the role of an order parameter. The temperature dependence of the specific heat and the susceptibility qualitatively agree with experiments.
Spin Green Functions for Ferromagnetic Films with Asymmetric Boundary Conditions
Authors: Kontos D.
Published: July 2007

A microscopic theory is employed to calculate the spin Green functions for thin films of Heisenberg ferromagnets. The effect of general asymmetric boundary conditions is considered including surface anisotropy (“pinning”) and variation of the exchange parameters. Results are also obtained for the spin wave spectrum and the layer magnetization.
Influence of Perpendicular Field on Magnetic Fluctuations in Thin Films
Authors: Duszewski J.
Published: July 2007

The dynamic behaviour of fluctuations in magnetization is considered in inhomogeneous systems represented by thin films in the presence of an external magnetic field perpendicular to the easy magnetization axis. The damping and the diffusion coefficients are evaluated as a function of the intensity of the applied field. The spin correlation time observed at the Curie temperature should depend on the perpendicular field because of the Curie point shift due to the perpendicular field influence.
Analysis of Shubnikov‐De Haas Oscillations in HgSe
Authors: Hein G.
Published: July 2007

For the description of beating effects and of the angular dependence of Shubnikov‐De Haas oscillations (SDH) of the narrow‐gap semiconductor HgSe, a method is developed which can be used to estimate parameters from measurements of the transverse SDH effect. Also the influence of quadratic terms in the energy versus magnetic induction relation of the Landau levels can be studied.
A Dynamical Theory for a Disordered Hubbard Chain far from Equilibrium. I. Extended Master Equations
Authors: Heiner E.
Published: July 2007

By use of Robertson's time‐dependent projector technique a system of 2N evolution equations is derived for a disordered Hubbard chain in the kinetic state. Making simplifying assumptions it reduces to two nonlinear partial differential equations.
Mössbauer Relaxation Spectra Due to Electric Field Gradient Reorientation and Nuclear Hopping for an I = 5/2 to 7/2 Nuclear Transition
Authors: Gorobchenko V. D. , Litterst F. J.
Published: July 2007

The shape of Mössbauer relaxation patterns is derived for a Mössbauer atom jumping in a tetrahedral cage with a correlated electric field gradient reorientation for an I = 5/2 → 7/2 nuclear spin transition. A stochastic relaxation model is applied.
Small‐Signal AC Response of Two‐Dimensional Hot Electrons in Quantum‐Well Structures of Polar Semiconductors
Authors: Bhattacharya A. , Ghosal A. , Chattopadhyay D.
Published: July 2007

Small‐signal ac mobility of hot electrons moving two‐dimensionally in the lowest sub‐band of a quantum‐well structure is studied on a drifted Maxwellian model incorporating polar optic and acoustic scattering. Numerical results are obtained for GaAs considering a dc bias field of 1 kV/cm. The small‐signal ac mobility is found to be constant up to 350 GHz at 77 K and up to 120 GHz at 120 K. The drift velocity, however, begins to lag behind the field from 50 GHz at 77 K and from 10 GHz at 120 K.
On Quasistationary States in the Multipulse Spin‐Locking
Authors: Feldman E. B. , Summanen K. T.
Published: July 2007

A new approach to the problem of quasistationary state analysis in the multipulse spin‐locking experiment is developed. The readjustments of the quasistationary states under the influence of multispin resonance processes are discussed. The quasistationary magnetization values obtained within the scope of the approach are compared with experimental data.
LCAO‐Xα Calculations of Transition Metal Clusters
Authors: Seifert G. , Eschrig H.
Published: July 2007

The electronic structure of some transition metal clusters (V6, Cr6, Cu6, Ag6) is studied by an approximate LCAO‐Xα scheme. Energy level spectra are discussed with respect to other theoretical investigations. The density‐of‐states curves are represented and compared with those from band‐structure calculations. The correlation between binding energies of clusters and the corresponding cohesive energies of the bulk material is shown. Furthermore, the binding energies in copper clusters versus cluster size are discussed. Finally, some experimental results according beams of copper clusters and ESR studies of matrix isolated copper clusters are explained briefly.
Multiple Scattering of Axially Channeled Particles by Thermal Vibrations and Electrons
Authors: Ivanov M. A. , Kvashnina L. B.
Published: July 2007

Within the framework of the classical small‐angle scattering theory a microscopic description of positively charged particle behaviour during axial channeling in a crystal is given. Assuming that statistical equilibrium in a transverse plane is established, the differential Fokker‐Planck‐type equation is obtained from the detailed‐balance relation. The coefficients of this equation are determined by the atomic scattering potential and distribution function of scatterers and are studied at various relations between the amplitude of the thermal atom vibrations and their screening radius. It is shown that for relatively small depths (high transverse energies) the processes of direct particle knocking‐out of a channel are predominant. At low transverse energies the scattering particle behaviour is determined by nuclear and electron diffusion processes. In this case, if the distance of closest approach of the particle to a chain exceeds considerably the amplitudes of atomic displacements, the corresponding coefficients are analogous to those obtained earlier.
Optical and Energy‐Dispersive X‐Ray Investigations of the Mixed Halide SmFCl
Authors: Bolduan F. , Hochheimer H. D. , Beck H. P.
Published: July 2007

The mixed halide compound SmFCl is studied at room temperature by X‐ray and optical investigations in order to look for a pressure induced structural or valence change. The results show that in the pressure range up to 22 GPa there is no structural change. Though also an abrupt pressure induced valence change (Sm2+ → Sm3+) is excluded the results are not in contradiction with the occurance of a gradual valence change.
Overshoot in Low‐Conduction Semiconductors
Authors: Gerlach E.
Published: July 2007

It is shown that semiconductors, for particular scattering mechanisms, may have a strong peak in the conductivity s̀′(ω), if the ratio of the dc‐scattering frequency and the plasma resonance frequency is larger than one. This peak immediately leads to a velocity overshoot for cold electrons, when applying an electric field pulse.
On the Nonlinear Light and Sound Absorption in Materials with Weakly Bound Atoms
Authors: Bonch‐Bruevich V. L. , Kakhlishvili T. Z.
Published: July 2007

Some optical and acoustical effects are studied which are due to the anharmonicity of vibrations of weakly bound atoms. Discontinuities are calculated of the sound absorption coefficient and of the real and imaginary parts of the differential dielectric permeability. Amplitudes are estimated of the vibrations corresponding to the nonlinear resonances at the frequencies ω = ω0/2 and ω = ω0/3, ω0 being the eigenfrequency in the linear regime.
Far‐Infrared Dielectric Function of Zincblende ZnS
Authors: Memon A. , Tanner D. B.
Published: July 2007

The complex dielectric response function of zincblende ZnS is determined at 300 K by dispersive Fourier transform spectroscopy. The frequency range studied, 150 to 450 cm−1, spans the frequency of the q = O transverse optic (TO) phonon mode. The frequency dependence of the anharmonic self‐energy function Γ(ν) of the q = 0 TO phonon is calculated from these data. The features observed in the spectrum of Γ(ν) are satisfactorily assigned to multi‐phonon processes by comparison to theoretical lattice dynamics calculations for cubic ZnS.
Structural Disorder Model of Amorphous Semiconductors Thermodynamics of a‐As
Authors: Vaid B. A. , Sharma K. C.
Published: July 2007

The structural disorder model of amorphous semiconductors, near the amorphous to crystalline transition, recently proposed, is generalized for triply coordinated As. The model is able to explain at least qualitatively the change in enthalpy and the configurational entropy during transition.
Static and Thermophysical Properties of Mixed Crystal Systems
Authors: Gupta B. R. K.
Published: July 2007

An analysis of the interionic potential is performed to study the static and thermal properties of KClKBr and KBrKI mixed crystals for the entire range of composition. The interionic potential consists of the long‐range Coulomb and three body interaction, the short‐range van der Waals attraction, and the overlap repulsion, effective up to the second neighbour ions. Instead of using the BM‐type short‐range potential the Hafemeister and Zarht (HZ)‐type repulsive potential is considered between the nearest as well as between the next nearest neighbours. The three body charge transfer parameter f(r) and repulsive hardness parameters are evaluated using respectively the Cochran formula and overlap integrals. The van der Waals interaction coefficients are determined using the Slater‐Kirkwood variational approach. The calculated values of cohesive energy, bulk modulus, and the pressure derivatives of bulk modulus for the mixed crystals under study agree fairly well with available experimental data. The results achieved by previous investigators are also shown for the sake of comparison with the present and experimental investigations.
Correlation and Spectral Properties of Individual Particles of Molecular Crystals with Isolated Point Imperfections
Authors: Vikhrenko V. S. , Kulak M. I.
Published: July 2007

The analogue of the dynamical equations for a crystal lattice is used to calculate the momenta time correlation functions and vibrational spectral densities of individual particles in heavy rare gas solids with defects. Some peculiarities in the behaviour of particles near a vacancy and light or heavy substitutional imperfections are discussed.
Some Comments and Corrections on the Defect Diffusion Models of Dielectric Relaxation
Authors: Bozdemir S.
Published: July 2007

An attempt is made to improve the “defect‐diffusion model” initially proposed by Glarum. Some of the basic ideas underlying the model and assessing its success and rationality as applied to polymer relaxation are discussed. The model is generalized by developing a new one‐dimensional “molecular chain‐defect diffusion model”, namely, extending the single dipole relaxation to a linear chain molecular system. A dipole correlation function derived from this new model under various physical conditions, appears in the form of the Williams‐Watts empirical decay function φ(t) = exp [−(t/τ)γ] with 0 < γ ≦ 1. The results obtained lead to a molecular interpretation of this “universal” non‐exponential decay function.
Anomalous High‐Temperature EPR Linewidths in the Spinel Solid Solution Cu2xCr2xSn2−2xS4
Authors: Colombet P. , Glaunsinger W. S.
Published: July 2007

The spinel spin‐glasses Cu2xCr2xSb2−2xS4 are studied by electron paramagnetic resonance in the temperature range 4 to 560 K. The linewidths at high temperatures are much larger than expected from magnetic measurements, and for 0.25 ≦ x ≦ 0.50 the linewidths are effectively dipolar although the lineshape is Lorentzian. The experimental and estimated exchange‐narrowed line‐widths at high temperatures are then compared for ferromagnetic‐antiferromagnetic and predominantly antiferromagnetic insulating spin‐glasses in which the magnetic ions occupy face‐centered‐cubic lattice sites or B‐sites of the spinel structure.
Umbrella‐Type Magnetic Structures in Diluted Ordered Lithium Ferrospinels
Authors: Maltsev V. I.
Published: July 2007

A symmetry analysis of ferrimagnetic structures is carried out in spinels that are isostructural with ordered lithium ferrite. The decrease of crystal symmetry due to the formation of atomic superstructure is shown to be a condition for realization of umbrella‐type magnetic structures in compounds of this class. The neutron diffraction data for lithium‐aluminium and lithium‐gallium ferrospinels are given which confirm the results of the theoretical treatment.
Specific Heat and Magnetocaloric Effects in TbPO4 1. Experiments
Authors: Üffinger G. , Kasten A.
Published: July 2007

At low temperatures TbPO4 undergoes two successive phase transitions. Antiferromagnetic ordering along the tetragonal c‐axis at TN1 = 2.28 K is followed below TN2 = 2.13 K by a structure of lower symmetry where the moments are tilted off the c‐axis by about 20°. The B‐T phase diagram (B along c) is determined down to 1 K by means of specific heat, adiabatic and isothermal field sweeps. In applied field there is an additional spin‐flop phase (between Bc1 = 0.61T and Bc2 = 1.06T in the limit T → 0).
Free Energy of the Amorphous Ferromagnets with Heisenberg Exchange Interaction and Liquid‐Like Disorder
Authors: Vakarchuk I. A. , Rudavskii Yu. K. , Ponedilok G. V.
Published: July 2007

A continuous integration method is used for the investigation of the Heisenberg quantum model with structure disorder. The free energy of such system is obtained as the perturbation theory series of the inverse cube of effective exchange interaction radius for arbitrary temperature and spin value. The contribution of magnetic and structure fluctuation effects to the thermodynamics, magnetization of the system, and temperature of the ferromagnetic phase transition is investigated. Numerical calculations on the base of model systems show that the change of critical temperature and low temperature magnetization at the amorphization of a crystal are in qualitative agreement with experimental results.
The Influence of Correlation and Band Structure Effects on an Exciton Weakly Bound to an Isoelectronic Impurity
Authors: Geistlinger H. , Weller W.
Published: July 2007

A variational method for the ground state of an exciton bound to an isoelectronic impurity is developed. In contrast to the HTL model the correlation between the electron and the hole is taken into account for the first time, using instead of the hole coordinates the relative electron‐hole coordinates. In this way it is possible to describe the whole region from strong exciton binding, where the HTL model is a good approximation, to the free‐exciton limit, impossible to reach in the HTL model. Furthermore, the method predicts a small potential region (≈ 10 meV) above the threshold for electron binding, where the exciton is still bound. Because the impurity potential is short‐ranged instead of the effective‐mass‐approximation a band structure parametrization of the lowest conduction band is used. As a numerical example the case of GaP:N is considered.