bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kondo‐Like Behaviour of the Electrical Resistivity of the Compound Pro0.25La0.75Al3
Authors: Lippold B. , Müller H. 
Published: July 2007

AbstractThe temperature dependence of the electrical resistivity of Pr0.25La0.75Al3 is investigated. The 4f part of the resistivity shows Kondo‐like behaviour. Using the experimental crystalline electric field splitting scheme and the Hamann factor, the 4f part of the resistivity can be fitted with the parameters ϱ = 0.139 μΩ cm, TK = 83.5 K, and S = 0.004.
Microscopic Model for the Ferroelastic Transition in KLiSO4
Authors: Žekš B. , Lavrenčič B. B. , Bling R. 
Published: July 2007

AbstractA microscopic model for the ferroelastic transition in KLiSO4 at Tc = 190 K is proposed. The model is based on the ordering of the “top” SO4 oxygen into one of the three off‐centre sites below Tc. It yields a transition of first order and agrees with the predictions of the Landau theory for the hexagonal‐orthorhombic equitranslational transition.
Short‐Range Order Model of GexS1−x Glasses and Utilization of This Model in Calculation of the Optical Gap and the IR 367 cm−1 Band Intensity
Authors: Černošek Z. , Černošková E. 
Published: July 2007

AbstractA short‐range order model (SRO model) of GexS1−x glasses is proposed and utilized to calculate the optical gap values and the IR 367 cm−1 band intensity. The optical gap values of the SRO model structural units are derived for calculation. Based on the description according to the SRO model it can be stated that the studied IR band is probably due to vibrations of the Ge‐S bonds in the (Ge‐S)n chains.
Theory of the Power Spectrum and Scattering Properties of Three‐Dimensional Disordered Systems Having a Variable Degree of Short‐Range Order. I. Continuous Spectrum
Authors: Celasco M. , Mazzetti P. , Stepanescu A. 
Published: July 2007

AbstractA new approach to power spectrum calculation of structures characterized by a spatial distribution of localized physical events, which has the advantage of being flexible enough to describe practically any type of local order and of giving the results in a very compact and general form, is given. Starting from a completely ordered three‐dimensional structure, with the elementary events arranged according to an arbitrary crystallographic order, the disorder is introduced by displacing the elementary events from their lattice position. The displacements are described from a probabilistic point of view by means of three general distribution functions which can be related to the interaction forces acting between nearest neighbour events and using a convolution technique for describing self‐consistently the whole structure, whose statistical properties remain translationally invariant. A simple analytic expression is obtained where different degrees of short‐range order with any local crystallographic configuration can be introduced and characterized.
Photo‐Induced Transformation of Close Frenkel Pairs in Strontium Fluorite
Authors: Eshita T. , Tanimura K. , Itoh N. 
Published: July 2007

AbstractLaser‐induced change is studied of the optical absorption and luminescence due to F‐H pairs generated by an electron pulse in SrF2. It is found that laser irradiation near 2.34 eV at a delay of 26 μs after an electron pulse by which F‐H pairs are generated reduces the component I of the pairs that has a decay time of 59 μs and optical absorption bands at 2.34 and 4.13 eV and enhances the component II that has a decay time of 7.7 ms and has optical absorption bands at 2.7 and 3.35 eV. Laser irradiation near 2.7 eV at a delay of 4 ms after the electron pulse is found to induce the reverse reaction. Studies of dichroism of the laser‐induced reduction and enhancement of the optical absorption bands and the luminescence reveal that the direction of the Σ‐Σ transition of the F molecular ion is converted by the transformation from I to II and vice versa. It is suggested that the component I corresponds to the F‐H pairs at nearest‐neighbour and II to those at the next‐nearest neighbour sites.
Diffusion Model for Charge Transport by Moving Dislocations in Simple Ionic Crystals
Authors: Tóth A. , Keszthelyi T. , Kálmán P. , Sárközi J. 
Published: July 2007

AbstractA diffusion model for the calculation of the charge transport caused by moving dislocations in simple ionic crystals is developed. The model is based on the assumption that the charge transport originates from the diffusional motion of vacancies under the influence of the potential field of moving dislocations. The numerical results obtained for LiF and NaCl doped with divalent cation impurities show that the assumed mechanism is suitable for the explanation of the main features of the experimental results.
Theory of the Dependence of the Phase Boundary of FeBr2 Metamagnet on Hydrostatic Pressure
Authors: Onyszkiewicz Z. 
Published: July 2007

AbstractA two‐sublattice Ising model is proposed with special four‐spin interactions added in order to describe the FeBr2 metamagnet. The important fact is that the four‐spin interaction terms are not even functions of spin sublattice operators. Thermodynamical properties of this model are investigated in the molecular field. The complete phase diagrams for FeBr2 as functions of hydrostatic pressure are obtained numerically. Moreover the theoretical results are compared with experiment.
Self‐Consistent Semi‐Classical Dynamic Theory of Non‐Radiative Capture and Emission Statistics in Defect Semiconductors
Authors: Mandelis A. 
Published: July 2007

AbstractA self‐consistent, semi‐classical theory of the non‐radiative capture and emission rates of carriers in defect semiconductors is presented. The lattice is treated in the configuration coordinate approximation and thermal averages of transition rates and cross‐sections are calculated in the experimentally important statistical limit. The semi‐classical theory gives explicit expressions for the time‐dependent transition rates following optical excitation of carriers initially trapped in defect states within the band‐gap of the semiconductor. In the steady state and in the thermodynamic limit, the predicted rates are in agreement with experiment. The theory bridges the gap in the literature between rigorous but complex quantum‐mechanical theories and rough but experimentally useful semi‐classical calculations, while it makes apparent the connection to Shockley‐Read statistics.
Low‐Temperature Pair Associates of H Centres in KBr
Authors: Akilbekov A. , Elango A. 
Published: July 2007

AbstractIn the course of investigating the annealing of KBr crystals X‐rayed at 4.2 K the creation of new pair associates of interstitial halogen atoms (di‐H centres) with an absorption band at 3.85 eV is detected. The 3.85 centres arise only as a result of thermodestruction of the well‐known di‐H centres with an absorption band at 4.4 eV. The properties of these new centres are studied and the possible ways of halogen association in KBr are discussed. As a model for the 3.85 centres a model of (Br)2 dimers is proposed, in which the optical transition differs from that in Br ions both by size and direction. The range of KBr absorption spectra between Br and Br absorptions (3.6 to 4.4 eV) is attributed to the absorption of (Br)2 dimers. The V4A centres in KBr with Li or Na impurities have obviously also a (Br−2)2 structure.
Ellipsometric Investigation of Lattice Vibrations in Anisotropic Systems. α‐Quartz
Authors: Jungk G. , Röseler A. 
Published: July 2007

AbstractThe ellipsometric equation for uniaxial crystals with the optic axis parallel to the reflecting surface is used to calculate the dielectric function from experimental data on α‐quartz in the range 700 < ω < 1200 cm−1. The experimental arrangement as well as the mathematical procedure are presented. The results confirm the known mode frequencies including the selection rules and show above the influence of many‐particle effects. The latter can be described approximately as for electronic spectra.
Analysis of the Short‐Range Repulsive Potential in Alkali Halides
Authors: Kaur A. J. , Bhende W. N. , Bakhshi P. S. , Shanker J. 
Published: July 2007

AbstractThe applicability of the Woodcock potential form is considered for studying the crystalline properties of alkali halides. This potential form represents the composite form of the inverse power dependence and the exponential dependence of the repulsive energy on interionic distance. The cohesive energy, pressure derivative of bulk modulus, thermal expansion coefficient, and the Grüneisen‐Anderson parameters are calculated for sixteen NaCl‐structure alkali halide crystals. The results are discussed and compared with available experimental data. The corresponding values obtained from the Born‐Landé inverse power form and from the Born‐Mayer exponential form are also presented for the sake of comparison. The important contribution is the finding that the Woodcock potential is applicable to all the three states viz. molecular state, liquid or molten state, and crystalline state of alkali halides.
New Approach to the Theory of Hybrid Excitations in Magnetic Dielectrics
Authors: Škrinjar M. J. , Kapor D. V. , Šetrajčić J. P. , Ivić Z. 
Published: July 2007

AbstractAn analysis is made of the magnetic and optical properties of an antiferromagnetic dielectric (AFD) in constant magnetic field. Hybrid excitations appearing in AFD during the single‐particle transitions represent a mixture of magnetic excitons and photons. The direct relationship between the average magnetic and electric dipole moment of the crystal is a consequence of the hybridization of elementary excitations. This relationship is described by the magneto‐optical tensor, which is expressed through the microscopic features of the system, more precisely, through electric dipole and magnetic dipole moments of the transitions in the paramagnetic ions in AFD.
Biexciton Two‐Photon Absorption and Raman Scattering in CuBr
Authors: Bobrysheva A. I. , Baltaga V. V. , Grodetskii M. V. 
Published: July 2007

AbstractThe probabilities of the two‐photon absorption by a biexciton in the ground and the first vibrational states in CuBr and the probability of the two‐photon Raman scattering with the participation of the ground and the first vibrational states of the biexciton as intermediate states are calculated by perturbation theory method. Supposing that a Lorentzian distribution of frequencies ωi of the exciting light and a Lorentzian shape of the emission lines of the excition occur, the shape of the emission line at different values of the biexciton half‐width Γm is calculated. The dependence of the Raman scattering maximum position on ωi is obtained. At the condition 2Γ ≧ Γm; Γ Γm ≦ Γf the experimentally observed deviation of the Raman scattering maximum shifting from 2Δωi, is explained. The polarizational properties of the Raman scattering probability are obtained including the case when the intermediate states are the biexcitons Γ1, Γ5, Γ3.
Electron States and Conductivity of Size Quantized Systems with Rough Boundaries
Authors: Potapenko S. Yu. , Satanin A. M. 
Published: July 2007

AbstractA new approach to the study of electron properties of the systems with rough boundaries is proposed. The boundary problem is reduced to the analysis of Schrödinger equation with effective Hamiltonian and boundary conditions for flat surfaces by using a curvilinear coordinate system. A criterion for existence of localized states is obtained and evaluation of the lifetime of resonance states arising near the bulges is presented. Asymptotic behaviour of the state density tails from the subbands of the size quantization, intraband and interband relaxation time, and conductivity of the film are estimated. The influence of the scattering by boundaries on the localization effects in two‐dimensional systems is investigated.
Pressure—Volume Relation in Intermediate Valence Compounds
Authors: Naudts J. , Werner A. , Hochheimer H. D. 
Published: July 2007

AbstractExperimental p—V data of the compounds YbO, Sm4Bi3, and TmSe are analysed using a simple thermodynamic model. Acceptable values are obtained for the density of states of the conduction electrons, the volume at which the bandgap closes, and the pressure dependence of the bandgap.
Asymtotic Medium Concept Applied to Correlated Point Scatterers in the Weak‐Scattering Limit
Authors: Solbrig H. 
Published: July 2007

AbstractThe concept of an asymptotic medium with a superimposed inhomogeneity shell about the source point is employed as an interpretation scheme for multiple‐scattering approximations to the averaged Green function. Including third‐order scattering (finite‐ranged pair correlation), analytical expressions are obtained for the index of refraction of the asymptotic medium and the reflection and transmission coefficients of the inhomogeneity shell as well as for the electronic density of states.
Impurities and Charge Compensation in Some Molybdenium Oxides
Authors: Grunin V. S. , Patrina I. B. 
Published: July 2007

AbstractThe role of impurities in the defect formation in MoO3 and Na2Mo2O7 crystals is discussed. The EPR spectra of the X‐ray and uv‐irradiation centres are investigated. The constants of the appropriate spin‐Hamiltonians are obtained. It is shown that the localization radius of an electron (or a hole) exceeds the interatomic distances, therefore the EPR spectra have a low symmetry with noncoincident axes of the A‐ and g‐tensors. The unpaired density distribution depends on the characteristics of the lattice and impurity cations such as the electronegativity, the coordination number, and the degree of the local environment symmetry distortion.
Theory of the Power Spectrum and Scattering Properties of Three‐Dimensional Disordered Systems Having a Variable Degree of Short‐Range Order. II. Line Spectrum and Cross‐Relation Technique
Authors: Celasco M. , Mazzetti P. , Stepanescu A. 
Published: July 2007

AbstractA new approach to the power spectrum calculation of the three‐directional distribution of physical events characterized by a variable degree of order, ranging from a perfect long‐range order to a complete disorder, including short‐range order properties, is given in Part I of the paper. In this second part simple analytical expressions of the line component of the power spectrum are obtained. The scattering properties of disordered or partially ordered atomic or molecular structures (like for instance, liquid crystals) are considered, concerning both, the diffuse and the line component of the spectrum. The case when in the local order different types of sublattices can still be identified is also considered. Applications of the above results include X‐ray and neutron scattering properties of disordered or partially ordered atomic or molecular structures concerning both, the line and diffuse component of spectrum, excess energy and power loss calculation in ferromagnets and superconductors, and physical properties of amorphous materials. Some of these applications will be discussed in a forthcoming paper.
Phonon‐Polaritons in Bilayer Systems. p‐Polarized Guided Wave Phonon‐Polaritons and Guided Wave Surface Phonon‐Polaritons
Authors: Wendler L. 
Published: July 2007

AbstractIn a bilayer system consisting of two dielectric media with local, frequency‐dependent dielectric functions in addition to the surface phonon‐polaritons other types of p‐polarized phonon‐polaritons, guided wave phonon‐polaritons and a new type guided wave surface phonon‐polaritons, can exist. These phonon‐polaritons are associated with electromagnetic fields having standing wave character in one or in both layers in the direction normal to the surfaces. The regions in the ω — k‖ plane where the different types of phonon‐polaritons of a bilayer system occur are discussed for the three physically different possibilities of combining two dielectric media. The dispersion curves and electric fields of guided wave phonon‐polaritons and guided wave surface phonon‐polaritons are calculated and presented in graphical form.
Role of the Excess Volume of Formation on Alloying
Authors: Alonso J. A. , González D. J. , Iñiguez M. P. 
Published: July 2007

AbstractIt is found that the virtual crystal model of a disordered binary alloy (in which the alloy is considered as an effective monatomic solid with atoms of intermediate characteristics between those of the two component metals) explains the tendency for a negative deviation of the alloy volume with respect to the volume predicted by Vegard's law. These volume deviations constitute an effective way of lowering the heat of formation of the alloy.
First‐Order Raman Scattering in RbCl Containing F‐Centres
Authors: Negi B. B. S. , Ram P. N. 
Published: July 2007

AbstractThe first‐order Raman spectra due to F‐centre in RbCl are calculated using a Green's function method. A simple impurity model including changes in nearest neighbour force constants is employed to calculated the Raman spectra in the A1g, Eg, and F2g modes and the results are compared with available experimental data. A 50% reduction in central force constants gives good account of the experimental values.
Spin‐Glass Behaviour in Disordered Hubbard Alloys
Authors: Fehske H. , Kolley E. , Kolley W. 
Published: July 2007

AbstractThe paramagnetism to spin glass transition in concentrated itinerant alloys AcB1‐c is studied on the basis of the random Hubbard model. Kakehashi's treatment of nonlocal spin fluctuations mapped onto an effective random‐site Ising model is combined with Nambu's Landau‐type order parameter expansion of the quenched averaged free energy based on the replica method. The temperature‐ and concentration‐dependence of the exchange couplings is determined by a self‐consistent CPA calculation. Numerical results are presented for nearest‐neighbour pair interactions, freezing temperature, specific heat, single‐site distribution functions, densities of states, and spin glass order parameters.
On the Fluctuations and Phase Transitions in Dicke‐Like Models
Authors: Loos J. 
Published: July 2007

AbstractThe fluctuation theory based on the functional integration method is developed for a multimode Dicke‐Hamiltonian with arbitrary spins and with antiresonant terms included. The effective classical Hamiltonian of the fluctuations is deduced and the equilibrium phase transition, the existence of soft modes as well as the general equations of state are discussed in this unified approach. The consequences of the rotating‐wave approximation are clearly distinguished. The solid state phenomena of the cooperative Jahn‐Teller effect and of spin‐reorientation are implied in these considerations.
Ultrasound Attenuation and Quantum Oscillations in BiSb Alloys
Authors: Dominec J. , Misek K. , Kraak W. , Herrmann R. 
Published: July 2007

AbstractThe attenuation of ultrasound is measured in Bi100−xSbx alloys (x = 0, 1.2, 4, 4.5, 5, 6.4) in an experimental arrangement, where the wave vector and the magnetic field are parallel to the trigonal axis of the sample. The period and the amplitudes of the quantum oscillations, analogous to the Shubnikov‐de Haas ones, are discussed.
The Effect of Temperature on the Optical Absorption Edge of Amorphous Thin Films of Silicon Monoxide
Authors: Al‐Ani S. K. J. , Hogarth C. A. , Waters D. N. 
Published: July 2007

AbstractThe analysis of the optical absorption edge as a function of temperature is discussed with particular reference to amorphous silicon monoxide films. The validity of the Urbach rule is investigated and the respective parameters are estimated. Experimental measurements on thin SiO films of the optical energy gap as the temperature is varied in the range 100 to 474 K, are reported and the results are discussed in terms of current theory.
Optical Properties of Bielectron—Impurity Complexes
Authors: Kovarskii V. A. , Sinyavskii E. P. , Chernysh L. V. 
Published: July 2007

AbstractA calculation of the energy spectrum of the bielectron‐impurity complex is performed. If the energy of relative motion of the two electrons which form the bielectron is much greater than the energy of the bielectron‐impurity interaction, the problem may be solved in the adiabatic approximation for the separation of “rapid” (bielectron) and “slow” motion of the bielectron as a quasiparticle in the field of the impurity potential. It is shown that the bielectron‐impurity complex spectrum has the form of an inverted hydrogenic series and near each line of the inverted hydrogenic series from the long wavelength region, the lines of the forward hydrogenic series are located. The intensities of phototransitions on the bielectron‐impurity complex levels are calculated, too. The dependence of the absorption light coefficient versus the main quantum number of the inverted hydrogenic series is investigated. The theory developed is compared qualitatively with experimental data.
Lattice Dynamics of Tetrahedral Compounds with the Local Heine‐Abarenkov Model Potential
Authors: Kagaya H.‐matsuo , Soma T. 
Published: July 2007

AbstractThe lattice dynamics of III—V and II—VI tetrahedral compounds is investigated using a recently presented binding force and the local Heine‐Abarenkov model potential. Numerical calculations on the phonondispersion curves are performed for GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, and CdTe. The resulting ones especially for TA modes are in good agreement with the observed data of the neutron scattering, contrary to those using the Ashcroft‐type potential.
Nonlinear Absorption in III—V Semiconductors
Authors: Sen P. K. 
Published: July 2007

AbstractA coherent radiation‐exciton interaction model is employed to study analytically the phenomenon of nonlinear absorption in important III—V semiconductors (viz., GaAs, GaSb, InSb, InAs), the crystals being irradiated by suitable lasers with energies (hω) nearly equal to the band gap energies (hωg). The nonoptical processesare accounted for phenomenologically by introducing a damping parameter into the equation of motion of the probability amplitude of the excited electron—hole pair state. The Wannier‐Mott type of exciton wave function is found to be responsible for the giant nonlinearity of the crystal absorption coefficient in the near resonant optical interband transition regime with h | ω ‐ ωg | of the order of the crystal exciton binding energy. The effect of renormalization of the crystal band gap in the presence of Coulomb interaction and Starkbroadening is also discussed.
Self‐Consistent Field Theory Applied to the Semiconductor Band Edge
Authors: Huhn W. , Stahl A. 
Published: July 2007

AbstractThe electrodynamics of a two‐band semiconductor with a direct gap is governed by a set of non‐linear constitutive equations which are an appropriate generalization of the Maxwell‐Bloch equations for two‐level atoms. The following quantities are connected by these equations: density matrices for electrons and holes, coherent exciton amplitudes, and self‐consistent fields. The equations are derived from a standard two‐band Hamiltonian by a thorough analysis of localization properties of electromagnetic quantities. As limiting cases the theory comprises: linear exciton polariton theory, self‐consistent field theory ofthe electron gas, Maxwell‐Bloch treatment of two‐level atoms.
On the Possibility of Bose‐Einstein Condensation and the Superfluidity of Frenkel Excitons
Authors: Šetrajčić J. P. , Kapor D. V. , Mirjanić D. 
Published: July 2007

AbstractThe characteristic time of exciton relaxation due to phonons is estimated, and as it turns to be smaller than the exciton lifetime, it is concluded that Bose‐Einstein condensation is possible in the system of Frenkel excitons. It is further shown that kinematical interaction obtained in the Boson representation due to the Paulionic character of the excitonic operators, causes the superfluid excitation transfer through the crystal.