bluuebunny/crossref_metadata_2025_split huggingface dataset:
EPR Study of Impurity Colour Centres in P‐State in Alkali Halides
Authors: Baranov P. G. , Khramtsov V. A. 
Published: July 2007

AbstractSeveral types of (Ga°), (In°), and (Tl°) centres in the P‐state are produced in NaCl and KCl crystals doped with gallium, indium, and thallium by X‐irradiation, followed by suitable thermal and optical treatments. The EPR spectra of these centres are studied and the parameters of the spin Hamiltonian are determined from these spectra. The hyperfine interaction constants of (Ga°) and (In°) centres in NaCl are found to be nearly equal to those of free gallium and indium atoms. The structure of the centers investigated is discussed. In NaCl: Sn and KCl: Pb crystals X‐irradiated Sn+ and Pb+ centres in the P‐state are observed. The 2S1/2 state Pb3+ centres are found to have anisotropic hyperfine interaction constants.
Coherent Potential Approximation of Short‐Range Order in Cluster Models of Alloys
Authors: Batirev I. G. , Katsnelson A. A. , Kertész L. , Szász A. 
Published: July 2007

AbstractIn cluster approximation of coherent potential method the density of electron states of transitional element alloys with short‐range order is obtained. On the base of these calculations the configurational part of the total energy is determined and the equilibrium value calculated of the short‐range order parameter on the first co‐ordination sphere. The obtained parameter of orderliness in most of the considered systems agrees by sign with the experimental data and qualitatively they depend on the concentration on the right way.
Zeeman Effect at the 3T1 → 3T1(P) Absorption Transitions of CdS:Ni2+
Authors: Broser I. , Germer R. , Schulz H.‐J. 
Published: July 2007

AbstractWith magnetic flux densities up to 10 T, Zeeman experiments are carried out on CdS: Ni2+ crystals at low temperatures. Shifts and splittings of the 3T1(F) → 3T1(P) absorption components are studied in polarized light for H ‖ c and H ⟂ c orientation. The static crystal field theory is not a sufficient theoretical concept to interpret the findings, dynamic interactions must rather be considered.
Polarons and Wannier Excitons in Anisotropic Polar Crystals
Authors: Pertzsch B. , Rössler U. 
Published: July 2007

AbstractFor the case of anisotropic band masses and anisotropic electron–phonon coupling the polaron problem is treated by the method of Lee, Low, and Pines. In the same case the phonon‐induced effective interaction between electron and hole in a Wannier exciton is an anisotropic generalization of the well‐known Haken potential. Self‐energy and mass renormalization of the polaron as well as the binding energy of the exciton and the influence of the different terms of the effective potential are discussed as a function of the parameters of anisotropy.
Adiabatic Variational Calculation of the Lattice Relaxation at Metal Surfaces
Authors: Hietschold M. , Paasch G. , Baktoš I. 
Published: July 2007

AbstractThe relaxation is considered of the top lattice plane on surfaces of simple metals which is determined by a minimum surface energy. A general formulation of the problem is given which allows clear classification of previous theoretical attempts and their comparison with the present model. The latter is based on a variational procedure in terms of the density functional formalism using a parametrized surface model with extended ion cores (Ashcroft model potentials). Especially stressed should be the adiabatic properties of the model consisting in the fact that the electron density changes when the ionic positions are shifted. Numerical results for (100)‐Li, (110)‐Al, and (111)‐Al surfaces are presented. The relaxations have different signs, and they are smaller than 2% of the interlayer spacing even for the case of Al where some LEED interpretations indicate large contractions.
Analysis of the Dielectric Behaviour of Alkali Halide Crystals
Authors: Shanker J. , Sundaraj R. 
Published: July 2007

AbstractAn analysis of the dielectric data at low temperature (2 K) and at room temperature (290 K) is performed for the entire family of NaCl and CsCl structure alkali halide crystals. The recent data on dielectric constants and their pressure and temperature derivatives are used to study the nature of some important physical quantities like the energy gap between bonding and anti‐bonding states, the Phillips‐van Vechten electronegativity parameter and the Szigeti effective charge parameter. Some interesting results are obtained using the Penn model for the electronic dielectric constant and the Lawaetz relation between electronegativity and effective charge parameters.
Dynamic Spin Susceptibility of an Interacting Electron Gas
Authors: Choudhury S. K. , Mohanty S. P. 
Published: July 2007

AbstractA simple theory of dynamic spin susceptibility χ(q, ω) of an interacting electron gas is presented by using the equation of motion method for the double time retarded Green's function. A suitable moment conserving decoupling approximation is used and an expression for χ(q, ω) is obtained which is quite general and results of all previous authors can be obtained from it in appropriate limits. The enhancement function I(q), in the theory shows a peak at q ≈ 2qF. By using a screened Coulomb potential and an effective mass approximation, the exchange enhancement of the spin susceptibility of alkali metals is calculated and the results agree quite well with experiments.
Tl− Centres in KCl Crystals
Authors: Ioan A. , Topa V. 
Published: July 2007

AbstractElectrolytic colouring at about 300 °C and 8000 V/cm, in KCl:T1+ single crystals with a 10−4 mol% concentration of T1+‐ions, gives rise to the appearance of two new absorption bands peaking at 4.35 and 3.35 eV. The modifications of the absorption spectra of the coloured crystals induced by different colouring conditions, by the recording temperature and by the heat treatments in argon, hydrogen, and water vapour atmospheres are investigated. All experimental data support the substitutional T1−‐ion model, proposed in this paper as the colour centre responsible for these two new bands.
On the Optical Properties and Electronic Structure of AgSbTe2
Authors: Baleva M. 
Published: July 2007

Abstractp‐type polycrystalline samples of AgSbTe2 are investigated. The reflectance and thermoreflectance spectra are measured and the results obtained are quantitatively interpreted. The absolute maximum in the reflectance spectra is found to be shifted to smaller energies in comparison to that of PbTe and the other lead compounds and AIVBVI tellurides. Two additional structures are observed in the thermoreflectance spectra of AgSbTe2 in comparison with PbTe. These structures and the shift of the maximum in the reflectance spectra are explained with imbedding the band structure of its binary analog PbTe into the AgSbTe2 zone.
Magnetic Field Effect on the Decay Times of KCl:Sn
Authors: Hizhnyakov V. , Kalder K. , Mihkelsoo V. , Niedrais H. 
Published: July 2007

AbstractThe effect of pulsed magnetic fields up to 15 T on the decay times of KC1:Sn AT luminescence is investigated at 4.2 K. The decay consists of two exponential components. The decay time of the fast component decreases from 3.3 × 10−3 s at H = 0 to 2 × 10−5 s at H = 15 T. Magnetic field dependences of the decay times are discussed in terms of a model with a strong interaction between the excited electronic states of Sn2+ centres and Eg vibrations.
Short‐Time Carrier Transport in Amorphous Pentacene
Authors: Hesse R. , Bässler H. 
Published: July 2007

AbstractMotion of holes generated in an amorphous pentacene layer by a N2 laser flash is examined within a time range 10 ns to 1 p. Pentacene layers are prepared by vapour deposition onto a substrate held a t 140 K. An initial current spike is observed which is attributed to motion of holes with an short‐time mobility of the order of 0.1 cm2/Vs. Subsequently, carrier trapping occurs a t a rate constant > 107 s−1. The temperature dependence of the mobility is interpreted in terms of hopping through an array of hopping sites distributed in energy according to a Gaussian distri‐bution function.
Boundary Conditions for Stimulated Raman Effect of a Semi‐Infinite Piezoelectric Cubic Crystal
Authors: Merten L. , Wenk J. 
Published: July 2007

AbstractThe boundary conditions on the surface of a semi‐infinite crystal are formulated and solved for the so‐called two‐beam method on condition of normal incidence. The solutions are three “reflected” and three coupled “transmitted” waves. The electric amplitudes of the “reflected” and “transmitted” waves can be represented by explicit formulae. For continuously decreasing electric amplitude EL of the pump wave (EL → 0) the solutions change continuously into the well‐known Fresnel formulae of classical crystal optics.
Coherence Properties of Dynamically Diffracted X‐Rays
Authors: Holý V. 
Published: July 2007

AbstractThe description of dynamical diffraction of X‐rays by means of the mutual coherence functions of primary and diffracted beams is presented. The mutual coherence functions of a beam diffracted from a plane‐parallel crystal in Laue geometry are computed and the influence of the crystal thickness on the coherence width is investigated. The possible method is shown for measurement of a mutual coherence function of an X‐ray.
Structure and Energy Levels of the Glide 60° Partial in Silicon
Authors: Jones R. , Marklund S. 
Published: July 2007

AbstractDeformation induced edge dislocations in Si are known to be dissociated into pairs of 60° partials and act as electrical recombination centres. The structure of this partial is investigated using isotropic elasticity theory and a simple core reconstruction is suggested. The effect of this reconstruction is to eliminate all dangling bonds leaving only an empty band in the upper part of the band gap.
Electron‐Phonon Interaction and Superconductivity in Metals
Authors: Jain S. C. , Kachhava C. M. 
Published: July 2007

AbstractA first principle derivation, in terms of electron‐ion pseudopotential and the phonon spectrum, is presented for the electron‐phonon coupling constant λ. The phonon parameters, needed in the calculation, are characterised by a single average square frequency, which is evaluated after Allen and Cohen. The computed λ, along with the values of Coulomb pseudopotential μ* and Debye temperature θD, leads to an over‐all satisfactory result for the transition temperature and isotope effect exponent according to the formulation developed by McMillan. Further, the calculations demonstrate unambiguously the existence of Matthias regularities.
Pseudocubic Angular Dependence of the M = − 1/2 to + 1/2 EPR Transitions for Ions with S = 3/2 Produced by Small Crystal Fields of Arbitrary Symmetry and Random Strains
Authors: Gehlhoff W. 
Published: July 2007

AbstractPrevious investigations of the angular dependence of the −1/2 ⟷ +1/2 transition which turned out to be pseudocubic in spite of lower centre symmetry are extended to the case of arbitrary symmetry. Moreover the influence of random strains is calculated. The result is that also in both these cases the centre of gravity of the line groups exhibits a cubic angular dependence. Thus in the case of unresolved structures and non‐detectable ± 1/2 ⟷ ± 3/2 transitions the exact symmetry of the centre cannot be directly deduced from the angular dependence. The contributions from the local lattice distortions to the cubic angular dependence vary essentially inversely with the square of the magnetic field and can be determined by measuring at different microwave frequencies.
Low‐Temperature Optical Properties of Impurity Aggregates in Pb2+‐Doped KCl Crystals
Authors: Mugeński E. , Damm J. Z. 
Published: July 2007

AbstractLow‐temperature absorption, emission, and excitation spectra of substitutional Pb2+ ions (2 to 100 ppm) in KCl crystals subjected to various thermal pretreatments are examined. The existence of two quite different aggregate types composed of Pb2+‐cation vacancy dipoles is ascertained. The aggregates of the first type, thermally stable below 80 °C, appear in samples stored e. g. at room temperature. Their optical properties (small changes in the original absorption spectrum, characteristic emission bands partially overlap that ascribed to the isolated dipoles) suggest a rather weak interaction between component impurity dipoles. The aggregates of the second type appear in samples annealed at higher temperatures up to 250 °C. Their optical properties (new distinct absorption bands, characteristic emission separated from that ascribed to isolated dipoles) suggest a strong interaction between component impurity dipoles. The optical properties (15 K) related with the above aggregates as well as with isolated dipoles and some unidentified aggregation products are compiled.
X‐Ray Determination of Bond Charges in Silicon
Authors: Pietsch U. 
Published: July 2007

AbstractA bond charge model is introduced for the reevaluation of X‐ray data for silicon with respect to the electron density. Spherical silicon atoms and bond charges are adjusted separatly. In contrast to the model of deformable valence orbitals the size and shape of the bond charge can be investigated directly. The results are compared with calculations from empirical pseudopotentials and from the Dawson model of deformable orbitals.
Phase Boundaries between the Paramagnetic and the Antiferromagnetic Phases and between the Paramagnetic and the Spin‐Flop Phases of the Heisenberg‐Ising Model
Authors: Katsura S. , Shimada K. 
Published: July 2007

AbstractThe phase boundary between the paramagnetic and antiferromagnetic phases, and that between the paramagnetic and spin‐flop phases of the Heisenberg‐Ising model with anisotropic exchange energy are calculated by the method of pair approximation. The critical field curves are satisfactory except at the very low temperature. The reliability of the critical field in the low temperature region is closely related to the problem of the appearance of the anti‐Néel point, and is discussed by calculating the values of the Néel point and the anti‐Néel point by the method of the square approximation and comparing them with those by the pair approximation.
Dielectric Properties of Bi1−xSbx Alloys at the Semiconductor‐Semimetal Transition
Authors: Rudolph R. , Krüger H. , Fellmuth B. , Herrmann R. 
Published: July 2007

AbstractThe composition dependence of the lattice dielectric constant of semiconducting Bi1−xSbx alloys is investigated by means of helicon wave propagation for B∥C1 in high magnetic fields in the neighbourhood of the semiconductor‐semimetal transition. In contrast to the smooth variation of the parameters of the isoenergy surface of the electrons, in the neighbourhood of the transition first a rapid increase of the dielectric constant is observed, followed by a discontinuous drop when the band overlap begins. The comparison with theoretical calculations allows the conclusion that the lattice dielectric constant must be correlated with the indirect band gap of the alloy – the parameter of the semiconductor‐semimetal transition.
Electronic, Structural, and Magnetic Properties of 57Fe Atoms Created by 57 Co Electron Capture Decay in CoF2 and in CoCl2− and FeCl2− Bispyridine Complexes
Authors: Friedt J. M. , De Jesus Filho M. F. , Sanchez J. P. 
Published: July 2007

AbstractA comparative investigation of the 57Fe absorption and emission spectroscopy data in hosts of CoF2, CoCl22py, and FeCl22py is reported in both the paramagnetic and antiferromagnetic phases of these compounds. The electron capture decay products are observed to coexist in the Fe2+ and Fe3+ ionic configurations in CoF2, while only the Fe2+ charge state is stabilized inFeCl22py and CoCl22py hosts. Distributions of hyperfine interactions are observed in the complex ligand compounds FeCl22py and CoCl22py, whereas there is no indication for such effects in the monoatomic ligand compound CoF2. This indicates unique unperturbed substitutional rest sites in CoF2, whereas in the other hosts, part of the decay products are observed in a distribution of defect sites.
The Kinetics of Stable Heterogeneous Binary Systems
Authors: Püschl W. , Aubauer H. P. 
Published: July 2007

AbstractAmong thermodynamically stable systems homogeneous one‐phase states are compared with two‐phase heterogeneous ones, while no restriction is made about the physical origin of stability. In the case of transitions from a one‐phase state to another one‐phase state or a two‐phase system, a continuous spectrum of relaxation times appears as a difference to a transition from a two‐phase to another two‐phase state: in this latter case one finds two processes of distinctly different rates in good agreement, with experiment. With the aid of a stochastic theory, containing elements of classical nucleation and coarsening theory, the early, as well as the late kinetic change of the size distribution function as well as of momenta, describing the system, are derived. This theory also allows for a rise of the number of zones of a phase during annealing as a contrary effect to coarsening.
Infared Spectra of the Neutron Irradiated Quasi‐One‐Dimensional Charge Transfer Salts TEA (TCNQ)2 and QN (TCNQ)2
Authors: Kamarás K. , Holczer K. , Jánossy A. 
Published: July 2007

AbstractThe infrared vibrational spectra of the organic quasi‐one‐dimensional charge transfer salts quinolinium (TCNQ)2, and triethylammonium (TCNQ)2 change markedly upon irradiation by high energy neutrons. A reduction of the intensity of some totally symmetric modes and an increase of visibility of other modes are observed in the irradiated samples. The results are discussed in the framework of the electron‐vibrational interaction theory. The doses required to obtain observable changes are relatively high and point rather to a model of simple electron coupled vibrational modes extended over a few molecules than to phase oscillations of a collective state with a long coherence length.
Temperature Dependence of Bond charge Vibration in Silicon
Authors: Pietsch U. , Unger K. 
Published: July 2007

AbstractWith help of a bond charge model introduced in a previous paper the thermal motion of the silicon atoms and that of the bond charge (BC) is separated. This analysis is made with structure factor data from silicon of Aldret and Hart, measured at two temperatures. The observed temperature dependence of the BC is caused mainly by the larger vibration amplitudes of the BC's in comparison with that of the Si atoms. Experimentally, a change of the BC amount is not detectable. The mean square displacement of the BCs is 4.2 times larger than that of the silicon atoms for 92.2 and 293.2 K, respectively. This fact is explained on the basis of the changing amount of the BC in the vibrating lattice, which corresponds to the results of calculations by Maschke and Baldereschi.
Radiation‐Induced Emission of F2 Centres in KCl
Authors: Chandratillake M. R. , Newton G. W. A. , Robinson V. J. , Rodgers M. A. J. 
Published: July 2007

AbstractAn emission has been observed in KCl single crystals subjected to 12 MeV electron pulses. The emission spectrum peaks at 1200 nm (1.03 eV) and has a temperature‐independent lifetime of 29.7 ns up to room temperature. Experiments with crystals previously irradiated to produce F and F2 centres showed that the emission mainly arose from direct excitation by the electron pulse of previously existing F2 centres. The lifetime data, but not the spectrum, are in good agreement with published data.
Magnetic Behavior of van Vleck Ions and an Electron Gas Interacting by Exchange
Authors: Palermo L. , Da Silva X. A. 
Published: July 2007

AbstractThe magnetic behavior of a model in which van Vleck ions, under the action of a crystal field, interacting by exchange with an electron gas is investigated. The condition of onset of ferromagnetism and the behavior of the critical temperature, band and ionic magnetizations (and susceptibilities) versus temperature, as a function of the band width, exchange interaction, and the crystal field splitting energy parameters are obtained within an approximation equivalent to a molecular field formulation.
Calculations of Solution Energies of Alkaline‐Earth Metal Ions in Alkali Halide Crystals
Authors: Urusov V. S. , Dudnikova V. B. , Garanin A. V. 
Published: July 2007

AbstractThe Born‐Mayer ionic theory of lattice energy is used to solve the problem of solution of B2+ ions in AX crystals with NaCl structure (A alkali metal, B alkaline‐earth metal, X halogen). About fifty combinations of initial parameters are obtained, by varying the ionic radii, polarizabilities, repulsion parameters, and pure AX and BX2 lattice energies. For example, there are four variants of the repulsion parameters: average ones and those determined from the elastic, di‐electric, and atomic spectral properties. The model is sufficiently accurate to yield reasonable values of solution energies for the most ionic impurity lattices (all fluorides, barium and strontium chlorides). Both, the “polarization catastrophe” (for large impurity ions on small cation sites) and lack of an ionic model for the Mg2+ impurities (except for fluoride) and all iodides are considered to be the main factors which reduce the calculation validity.
Lattice Sums on Noncentrosymmetric Cubic Ionic Crystals
Authors: Jain A. K. , Verma M. P. 
Published: July 2007

AbstractGeneral connections between lattice sums of a definite kind, corresponding to all the cubic ionic crystals are derived and discussed. Tables of values of certain sums are given which together with the tables earlier published and the relations in the present paper can give any of the lattice sums of the class considered dor all the cubic ionic crystals.
Raman Scattering of Light in Antiferromagnetic Chromium
Authors: Cuden C. B. , Mota R. 
Published: July 2007

AbstractRaman scattering of light in antiferromagnetic chromium is discussed in terms of conventional second‐order time‐dependent perturbation theory. The scattering cross‐section as a function of frequency and temperature is calculated for the scattering of light by one‐electron, one‐hole, and electron‐hole pair excitations. It is shown that the unphysical divergence of the scattering crosssection for the photon energy transfer equal twice the antiferromagnetic energy gap found by Kwok, Woo, and Jha is removed by taking properly into account the statistical coherence factors.
Role of Magnetization in the Electron Quasiparticle Energy in the s–d Model of Ferromagnetic Semiconductors
Authors: Čápek V. 
Published: July 2007

AbstractIt is shown how the method of momenta based on fitting the lowest momenta of the spectral function may be reconciled with general arguments requiring that the magnetization can enter neither the position nor the form of quasiparticle peaks in the spectral function. The magnetization then enters just the weights of quasiparticle poles. Therefore, the temperature dependence of the quasiparticle energies strongly suppressed, in contrast to most of the contemporary theories.
Calculation of Vibrational State Density and Long‐Wavelength Spectral Density of Compositionally Disordered Chains
Authors: Böttger H. , Kleinert P. 
Published: July 2007

AbstractThe problem of a possible disorder induced reflection of the vibrational state density in infrared and Raman spectra is studied for simple mass disordered chains. The state density and the long‐wavelength spectral density are calculated exactly for the case of infinite mass impurity atoms and approximately by an embedded cluster method, which is applicable to systems with arbitrary impurity mass. A remarkable resemblance between state density and spectral function can occur.