bluuebunny/crossref_metadata_2025 huggingface dataset:
On the decay properties of the M′ center in LiF crystals
Authors: Bosi L. , Nimis M.
Published: July 2007

For the first time properties concerning the luminescence decay time as well as the relative quantum yield of M′ center in LiF X‐ray irradiated samples are simultaneously and accurately investigated as a function of temperature in the range 12.5 to 335 K. Some discrepancies are found between the decay time values and those obtained by other authors in incomplete runs of measurements. The explanation of this difference may be connected to the coloration process and in particular to the generally high M′ center concentration: on the contrary the M′ center concentration in the samples investigated is low but nevertheless typical for laser operation. Data analysis indicates that more than one nonradiative process is involved in the M′ center decay. It is also ascertained that at fixed temperatures the decay time is independent of the M′ center concentration in the range investigated (i.e., restricted to low concentrations) and of the ageing of the samples.
Local phonons in crystals with electron centres
Authors: Lakhno V. D. , Chuev G. N.
Published: July 2007

The changes are investigated in the phonon spectrum for the F‐centre in the presence of excess electron. The frequencies of local phonons for the ground and the first excited self‐consistent states of the F‐centre in KC1 are calculated. The adiabatic approximation is used to determine a secondorder correction to the energy for self‐consistent states in the F‐centre. As a limit the resting polaron is considered. For excited self‐consistent states local modes are found with frequencies larger than in optical phonons. It is also found that excited self‐consistent states of the polaron show a phonon (pseudo Jahn‐Teller) instability.
Green functions for polariton modes in magnetic superlattices
Authors: Raj N. , Tilley D. R.
Published: July 2007

The linear response of magnetic‐polariton modes in an infinitely extended magnetic superlattice to an r.f. applied magnetic field is considered. The resulting Green functions are given in mixed position, wavevector form and also in wavevector, wavevector form. As is expected, the poles of the derived Green functions give the dispersion relations for magnetic polaritons in a bulk magnetic medium and also in a magnetic superlattice.
Construction and application of the Green's function for stepwise constant potentials
Authors: Trott M. , Schnittler Ch.
Published: July 2007

The path‐integral‐inspired approximation method is a convenient tool for the construction of a WKB‐like Green's function. This method is generalized to the case of potentials with finite steps by investigating the exact Green's function of a single finite step. To demonstrate the utility of this method the single quantum well is studied in detail: For the stepwise constant potential the density of states of the bound as well as of the continuum states is given. For a smooth potential bottom semiclassical quantization rules are derived for different band bendings. The series representation of the Green's function allows the derivation of an appropriate local density of states necessary for a modified Thomas‐Fermi approximation.
Distortion of the crystal field in the van Vleck paramagnet LiTmF4 activated by isovalent impurities
Authors: Aminov L. K. , Vinokurov A. V. , Kurkin I. N. , Kostetskii Yu. Yu. , Korableva S. L. , Salikhov I. Kh. , Sakhaeva S. I. , Teplov M. A.
Published: July 2007

The spin‐lattice relaxation times of Ce3+, Nd3+, Yb3+ ions are measured in LiTmF4 single crystals at temperatures (1.6 to 5.0 K) and frequencies 9.4 and 23.0 GHz. An observed exponential dependence of the relaxation rate on temperature, T ∼ exp (−Δ/kT), shows that relaxation proceeds through Van Vleck Tm3+ host ions, and for the Nd3+ ion it is possible to distinguish the contributions to relaxation of the nearest and more distant coordination spheres. The distinction of the activation energy Δ from the excitation energy of the lowest Tm3+ doublet state in the ideal crystal (32 cm−1) is explained by a strong distortion of the crystal field at the Tm3+ ions nearest to the impurity. Investigations of the optical absorption spectra of Tm3+ ions in pure and doped LiTmF4 single crystals are in good agreement with this point of view.
Wannier functions for d‐band of ferromagnetic nickel
Authors: Modrak P. , Wojnecki R.
Published: July 2007

The method of direct variational calculation of Wannier functions is applied to the ferromagnetic nickel. The calculations are performed within the framework of the unrestricted Hartree‐Fock theory. The Slater‐Koster parameters obtained are compared with other results and with the parameters used in model Hamiltonians for ferromagnetic nickel.
Temperature dependence of carrier trapping in bulk vitreous GeSe3 from transit time measurements
Authors: Calas J. , Abdel‐maksoud S. , Averous M.
Published: July 2007

Transit time measurements in the low signal approximation are reported for bulk vitreous GeSe3. The temperature range investigated is 100 to 300 K. The shape of the transient current can only be explained by a model with two trapping centers, a shallow one and a deep one. The shallow level is described by Tt1 and Td where Tt1 and Td are the times spent in the free state and on the trap, respectively. For the deep level the probability for a carrier reemission is neglected; the time Tt2 spent in the free state before trapping is only taken into account. The spectral sensitivity for photocarrier creation is also given with a maximum at 2.7 eV, i.e. higher than the energy of the band gap.
Anomalous magnetic field dependence of electron mobility in anisotropic ferromagnetic semiconductors
Authors: Okladnoy Yu. G.
Published: July 2007

The magnetic field dependence of the electron mobility in an easy‐axis ferromagnetic semiconductor is investigated for the case when the magnetic subsystem is described by a Heisenberg Hamil‐tonian with a weak anisotropy. It is found that, under definite conditions, the transversal magnetic field leads to an increase in magnon concentration and, accordingly, to a decrease in the electron mobility, while for isotropic ferromagnetic semiconductors only a decrease of the concentration and an increase of the mobility can take place for increasing magnetic fields.
Determination of deformation potential constants of arsenic
Authors: Golban I. M.
Published: July 2007

The galvanomagnetic coefficients of arsenic are calculated by means of a variational method taking intravalley scattering of charge carriers on longwave acoustic phonons into account. The experimental data of galvanomagnetic phenomena in weak magnetic fields are processed with the help of the formulae obtained and the constants of deformation potentials of electrons and holes are calculated in a wide temperature range (77 to 305 K).
The behaviour of the vortex state in magnetic superconductors
Authors: Saif A. G.
Published: July 2007

The distribution of the magnetic field inside a ferromagnetic superconductor (FS) is developed. The behaviour of the surface pinning in different geometries of FS system is considered. It is shown that, for FS systems, the superheating field is of the order of thermodynamic critical field for magnetic superconductors, H.
Mössbauer lineshape in the case of diluted ferromagnetic alloy thin films
Authors: Urbaniak‐Kucharczyk A. , Osetek Z.
Published: July 2007

The theory of Mössbauer line shape in fluctuating environment is applied to the case of thin film of a diluted alloy. The distribution of the spin autocorrelation time characterizing the line shape in the vicinity of phase transition point across the sample is calculated. It is shown that the change of concentration of magnetic atoms in diluted alloys leads to a variety of Mössbauer spectra at the same sample temperature. All the results obtained are calculated for the particular case of S = 1/2 and for a film with b.c.c. lattice, although another crystallographic lattices may be consider as well.
The Ising model of the two‐dimensional quasiperiodic lattice
Authors: Doroba A. , Sokalski K.
Published: July 2007

The magnetic structure of a two‐dimensional system of Ising spins arranged in the Penrose‐like lattice is investigated by means of the Bethe‐Peierls‐Weiss method applied to the nonperiodic lattice. Six types of spin‐sites are distinguished and seven exchange integrals depending on the spin enviroment are introduced. It is checked that this method applies only to the case of all nonzero exchange integrals. Phase diagrams and the thermodynamic and magnetic quantities for various points in parameter space are calculated. The stable and unstable magnetic ordered phases are found. For the antiferromagnetic case points of full compensation appear.
On the relation between structural phase transitions and spin reorientation transition in anisotropic ferromagnets
Authors: Schreiber J. , Bläsing J. , Flach S.
Published: July 2007

On the basis of Hollstein‐Primakoff transformation for the Heisenberg model with anisotropy a new theoretical description of the spin reorientation transition in ferromagnetic systems is given. An effective Hamiltonian is derived, which is identical with the scalar Φ4‐lattice model of structural phase transitions. Especially the appearance of precursor clusters of the low temperature phase above the phase transition point is discussed. If the reorientation transition takes place at sufficiently low temperatures the existence of defect pinned cluster states can lead to glass‐like behaviour. Experimental consequences are considered. In relation to the anomalous properties of high‐Tc superconductors special attention is paid to the importance of a crossover from a soft mode or mean‐field‐like behaviour into the regime of cluster fluctuations in strongly non‐linear dynamical systems.
The coexistence of unstable, metastable, and separated Frenkel pair defects in solids. III. Theory of the non‐impact mechanisms for defect formation in non‐metals
Authors: Dzhumanov S. , Khabibullaev P. K.
Published: July 2007

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

An exact analytical solution is found for the Ising model consisting of central and three side chains. It is shown that a doubling of the specific‐heat maximum can occur in the vicinity of lines separating the ground state phases of such a system.
Electronic Structure and Magnetooptical Effects in γ‐Ln2S3
Authors: Babonas G. , Dagys R. , Pukinskas G.
Published: July 2007

Faraday rotation and magnetooptical polar Kerr effect are studied in γ‐Ln2S3 crystals. The peculiarities of the magnetooptical spectra in Ln2S3 are interpreted on the basis of the regularities of f–f and f–d transitions in free Ln3+ ions taking into account the mixing of the excited localized and band states.
Resonant Raman Scattering in ZnxHg1–xSe
Authors: Kumazaki K.
Published: July 2007

Raman scattering by phonons is measured in narrow‐gap semiconductor, ZnxHg1–xSe, with x = 0 to 0.4 on (100) surface near the E1 + Δ1 energy gap at room temperature. Plasmon–LO phonon coupling modes are explained by a model taking into account the two‐mode behaviour of TO phonons. The photon energy dependence of scattering intensity shows a strong enhancement near the E1 + Δ1 energy gap. The results obtained from the experiments are compared with the results of Raman scattering, far‐infrared reflection, and ellipsometric measurements of other narrow‐gap semiconductors.
Triplet Molecular Excitations in Potassium Halide Cyanide Crystals. I. The CN– Impurity Centre
Authors: Camargo S. S. , von der Weid J. P.
Published: July 2007

The decay kinetics and emission intensity of the UV emission associated with the a3II → X1Σ+ electronic transition of the CN– molecular ion in potassium halides are investigated between 10 and 450 K. Two different energy transfer mechanisms from the host crystal to the impurity molecules are observed: the free exciton diffusion and the thermally activated migration of VK centers. A non‐radiative process is observed at high temperatures and is attributed to the coupling of the molecular excitation to local lattice phonons, probably the breathing mode of the neighbouring cations.
Free Energies of Polyatomic Polarizable Dipole‐Active Particles in Polar Media
Authors: Marsagishvili T. A. , Machavariani M. N.
Published: July 2007

A calculation method is given of free energy change of polyatomic polarizable dipole‐active particles at their dissolution in inhomogeneous polar media. Two mechanisms of interaction between the particles and polar media are considered: solvatational and fluctuational mechanisms including ion–dipole and dipole–dipole interactions. Received analytical expressions permit to carry out the calculations for the dissoluted particles with any finite number of intramolecular degrees of freedom, taking into account the spatial and frequency dispersion of media.
Thermodynamics of Deformation under Irradiation
Authors: Sarce A. , Savino E. J.
Published: July 2007

An irreversible thermodynamic model is proposed for describing the deformation of a crystal under stress and irradiation. A thermodynamic inequality is found to relate the lattice straining and stress with the irreversible part of the free energy density. As an application of the model the case of straight dislocation climbing under irradiation is studied.
Crystal Dynamics of F.C.C. Inert Gas Solids
Authors: Mishra S. K. , Singh T. N.
Published: July 2007

Results for the phonon dispersion curves along the [ζ00], [ζζ0], [ζζζ], symmetry directions and the Debye characteristic temperatures for Ne, Ar, Kr, and Xe rare gas solids are obtained on the basis of a five‐parameter non‐central force model. These results are compared with the experimental values with remarkable success. The Cauchy discrepancy is also explained on the basis of the model.
Phonon Dispersion in an α‐Perylene d12‐Crystal at 10 K
Authors: Schleifer J. , Kalus J. , Schmelzer U. , Eckold G.
Published: July 2007

Phonon dispersion curves for the 24 external and some of the internal modes in α‐perylene‐d12 (C20D12) are measured at 10 K for the [ζ00], [0ζ0], and [00ζ] directions by coherent inelastic neutron scattering and Raman scattering. Calculations are performed with a semi‐rigid‐molecule‐model, based on well‐known 6‐exp‐potential functions. The agreement between measurements and calculations is satisfactory. Because of strong mode coupling the identification of the character of the closely neighbouring phonons is often not unique.
Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. II. The Cubic–Monoclinic Phase Transition of Pure Rubidium Cyanide
Authors: Yang Zhengju , Luty F.
Published: July 2007

The cubic–monoclinic structural phase transition of RbCN is investigated with the elastic dipole model. The calculation shows that the monoclinic structure of RbCN consists of two groups of dipoles of equal number but aligning in two different orientations, which are obtained from the strain of the unit cell in agreement with the experiments. A stable configuration of the two groups of dipoles is proposed. The alternate displacement of the cations calculated from this configuration agrees with the experiment in direction but is too large in magnitude due to the elastic continuum model used. The interaction between neighboring dipoles is the main part of the ordering energy in contrast to the ferroelastic case of KCN. In fact a new kind of ordering transition – antiferroelastic phase transition – is proposed for RbCN.
Nonlinear Optical Nutation on Interexciton Transitions in Cu2O. Analogue of the Equidistant Three‐Level System
Authors: Shmiglyuk M. I. , Bardetskii P. I. , Tiron S. D.
Published: July 2007

The nonlinear nutation on the optical transitions between the IS(Λ) and 2P(Λ, 2Λ, Λ, Λ) exciton states of the Cu2O yellow series is studied theoretically. An idealized case is considered when one coherent excitonic mode of a macroscopic amplitude is created in the 2P(Λ) state by the external resonant pumping. It is shown that in this case the CO2‐laser induced dipole transition scheme is the same as for the model equidistant three‐level system. The evolution of the nonstationary state of the exciton–photon system to the stationary one due to the polarization damping is considered. The phase diagrams are investigated both, at strong and weak damping.
A Weak‐Coupling Calculation of the Binding Energy and Effective Mass of a Polaron in a Multiple Quantum Well
Authors: Lai W. , Butcher P. N.
Published: July 2007

The Fröhlich electron–phonon interaction in a multiple quantum well structure (MQW) is studied in a perturbation scheme. The dispersion relation of the polaron is obtained with an analytic form factor in a well and an overlap factor between wells. The polaronic binding energy and effective mass are compared with results for a single quantum well.
On the Theory of Auger Recombination in Disordered Semiconductors. A Green's Function Approach
Authors: Quang Doan Nhat
Published: July 2007

A Green's function approach based on the density‐operator formalism is developed to calculate the lifetime of Auger recombination in disordered semiconductors, taking explicitly into account translation‐symmetry breaking and the contribution of band‐tail states. The theory is applied to disordered materials which can be described by the smooth random field model. It is shown that the classical approximation is sufficient to produce the effect of the disorder on Auger recombination processes. Then a general expression for the Auger lifetime is derived in the form of the volume and configuration average of a local lifetime. The influence of the random field is reduced to a modification of the energy conserving δ‐function and the distribution functions of non‐equilibrium carriers. The Auger lifetime or recombination rate depends on the mean square of the random potential fluctuation, Ψ1. In the case of nondegenerate semiconductors, the Auger recombination rate is exponentially enhanced with increasing Ψ1, so that an estimate of the random parameter might be possible from Auger lifetime measurements. As an example, the Auger coefficient for p‐type GaSb is evaluated for the case of the random field due to thermal fluctuations of charge carrier concentrations.
The Hyperfine Field Distribution in Thin Films of Binary Diluted Alloys
Authors: Urbaniak‐Kucharczyk A.
Published: July 2007

In amorphous ferromagnets spatially fluctuating exchange interaction give rise to a critical behaviour substantially different from crystalline magnets. Within the framework of a molecular field theoretical approach, a non‐local Landau‐Ginzburg equation is applied for thin amorphous film in the vicinity of phase transition point by means of a correlated molecular field, which can only vary on larger scale than the spin correlation length. Therefore, the manner how the structural disorder affects the critical behaviour changes with temperature. The calculation of the hyperfine field distribution measured in the Mössbauer experiment is done for the case of a binary alloy with simple cubic lattice. Numerical results for various surface parameters and temperatures are obtained.
Correlation between the Mössbauer and Semiconductor Parameters of Tin Telluride
Authors: Motiejūnas S. , Baltrūnas D. , Gečiauskaitė N. , Makariūnas K.
Published: July 2007

The observed correlation between the 119Sn Mössbauer isomer shift δ and the hole concentration in tin telluride is explained on the basis of the latest literature data on the peculiarities of the peculiarities of the band structure. It is evaluated that the temperature change from 40 to 400 K should not influence the isomer shift.
Kondo Effect and Direct Interaction. Renormalization‐Group Approach
Authors: Allub R.
Published: July 2007

Wilson's renormalization‐group approach is used to study the magnetic susceptibility of a model with two different magnetic impurities. The particular case is considered in which only one impurity is coupled to the conduction band (Kondo coupling) and there is a direct interaction (JL) between the two impurities. For ferromagnetic interaction (JL > 0) between the localized impurities, a magnetic ground state is found and a divergent susceptibility at low temperatures. For (JL < 0), two different Kondo temperatures and a nonmagnetic ground state are distinguished.
The Irreversibility and Viscosity Effects in Dilute Ferrimagnets
Authors: Efimova N. N. , Popkov Yu. A. , Tkachenko N. V.
Published: July 2007

An investigation is made of magnetic viscosity and irreversibility in systems with short‐range superexchange (dilute ferrimagnetic oxides), where these effects are directly to the nature of the spin glass (SG) state. It is found that the irreversibility effects may be attended by other characteristic features of the SG state (the magnetic viscosity, the dependence of the low temperature behaviour of σZFC (T) on the field H), or alternatively, may exist without them, and are proper to various magnetic states: SG, superparamagnetic, as well as non‐collinear and disordered ferrimagnetic ones. In contrast, the existence of the logarithmic‐low magnetic viscosity is uniquely associated with the SG state.
Surface Spin‐Wave Mode Excitation in Bulk Amorphous FeNiB Alloys
Authors: Frait Z. , Fraitová D.
Published: July 2007

Experimental data on the surface spin‐wave mode excitation and magnetic surface anisotropy energy obtained by the method of ferromagnetic resonance and antiresonance are presented for as‐prepared and annealed bulk samples of amorphous alloys FexNi1−xB0.2, x = 0.4 to 0.7. For x = 0.4 the temperature interval 200 to 650 K is investigated, for x = 0.5 to 0.7 RT‐results are introduced.
Reflectivity Spectra and Band Structure of the Zinc and Cadmium Diphosphides
Authors: Sobolev V. V. , Kozlov A. I. , Polygalov Yu. I. , Tupitsyn V. E. , Poplavnoi A. S.
Published: July 2007

Precision reflectivity spectra of the tetragonal ZnP2, CdP2 for E ∥ c, E ⟂ c and monoclinic ZnP2 for E ∥ a, E ∥ b, E ∥ c are investigated at 80 and 293 K. New reflectivity structures are observed including the exciton peaks in the monoclinnic ZnP2. The thermoreflectivity spectra of CdP2 are obtained at 193 K. The band structure of the tetragonal ZnP2 and CdP2 and CdP2 is calculated using the pseudopotential method at the symmetrical points T, Z, A, M, R. A comparison of the reflectivity data with the results of the ZnP2 band structure is made.
Crystal Structure and Magnetooptical Properties of Cd1−xMnxTe with High Mn Concentrations
Authors: Babonas G. , Galazka R. R. , Pukinskas G. , Šileika A.
Published: July 2007

Cd1−xMnxTe crystals with compositions 0.1 < x < 0.7 are studied. It is observed that in Mnconcentrated crystals (x = 0.40, 0.64) are structural peculiarities which cause extra reflections in the Laue and Debye‐Sherrer patterns and the optical anisotropy of those samples. In Cd1−xMnxTe samples with x = 0.64 the effective birefringence is 4.2 × 10−3 and the splitting of the exciton peak is equal 0.7 meV. The dispersion of the Faraday rotation at 300 K is well described by a single‐oscillator approximation for all the investigated Cd1−xMnxTe crystals. In the region of the absorption edge of highly Mn‐concentrated crystals the magnetic circular dichrosism specta have additional contribution which can be related with an excitation of Mn2+ ions. In these crystals the temperature dependennce of magnetic circular dichroism in reflectance shows some peculiarities which are interpreted by the influence of antiferromagnetic interaction between the Mn2+ spins.
Local Static and Dynamic Atomic Displacements in Disordered Niobium Carbide
Authors: Gusev A. I. , Rempel A. A.
Published: July 2007

A neutron diffraction study is made of disordered niobium carbide NbCy (1.00 ≧ y ≧ 0.75) in the region of its homogeneity. The dependences of the mean‐square static and dynamic displacements of atoms on the composition of niobium carbide are determined. It is suggested that in niobium carbide localized metal—carbon bonds predominate over delocalized metallic interactions.
A Study of the Second and Third Neighbour Structure in Chalcopyrite CuGaSe2 by EXAFS
Authors: Antonioli G. , Lottici P. P. , Razzetti C.
Published: July 2007

EXAFS measurements on CuGaSe2 at the Ga, Cu, and Se K‐absorption edges are performed and the second and third shells of atoms around the absorbing one are considered. It is shown that an investigation up to the third neighbours by standard EXAFS data analysis techniques, in the usual approximations, gives reliable results in this complex structure. The EXAFS spectra can then give useful information on the structural distortions in the tetragonal chalcopyrite compounds.
A Study of Interstitial Impurity Diffusion by the Linear Response Theory
Authors: Kogutyuk I. P. , Keivan P. N. , Rarenko I. M.
Published: July 2007

The diffusion of interstitial impurities is studied within the linear response theory using Hamiltonian describing localized and quasi‐free states of impurity particles, as well as their interaction with lattice vibrations. The diffusion coefficient for light impurity atoms is shown to deviate from the Arrhenius‐type linear dependence ln D ∼ 1/T at high temperatures.