bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Thermodynamic Theory of the Improper Antiferroelectric Phase Transition in ADP
Authors: Konwent H. , Lorenc J. 
Published: July 2007

AbstractThe thermodynamic theory of the elastic and dielectric properties of ammonium dihydrogen phosphate is developed on the basis of the improper phase transition. By the representation analysis the transformation properties of the two‐component order parameter are investigated and the thermodynamic potential of the Landau type describing both elastic and dielectric properties (triggered by the order parameter) is derived, which correctly describes the space group symmetry change at the transition point. Its minima and their stability conditions are also studied. The temperature dependence of the spontaneous deformations and material constants is analysed in detail and consistency with the available experimental data is briefly discussed.
High‐Temperature Series in the Quantum‐Classical Heisenberg Model
Authors: Wydro T. 
Published: July 2007

AbstractThe recently introduced quantum‐classical Heisenberg model is investigated in terms of the high‐temperature cumulant expansions. The cumulants of the diagrams up to l = 7 lines and the lattice constants of the diagrams up to l = 6 lines for inhomogeneous p.t. and f.c.c. lattices are calculated. The model parameter y expressing the relative magnitude of two types of coupling constants is taken into account. High‐temperature series for the zero‐field susceptibility are constructed for ten values of parameter y and for both p.t. and f.c.c. lattice structures. The Padé analysis of the series is performed. Critical temperatures and critical indices of susceptibility are estimated.
Statistical Theory of Electrical Resistivity of Magnetic Ternary Alloys with Partial Long‐Range Order
Authors: Richter R. , Goedsche F. , Vojta G. 
Published: July 2007

AbstractWithin the framework of the coherent potential approximation the de electrical resistivity is calculted for random ternary substitutional magnetic alloys with partial atomic long‐range order. The special case of nonmagnetic alloys with potential scattering only is included. The case of a two sublattice system with two long‐range order parameters is studied. The spin‐disorder contribution to the resistivity is treated using the s–d exchange model. The calculations are done for a single‐band tight‐binding model with diagonal disorder, three kinds of localized spins, arbitrary concentrations, and arbitrary order parameters. A general closed resistivity formula in terms of alloy, spin, and order parameters is given in second order of the scattering potential and is discussed for a number of special cases including antiferromagnetic ordering.
Microwave Spectroscopy in Semimetallic Bismuth–Antimony Alloys
Authors: Braune W. , Kuka G. , Gollnest H.‐J. , Herrmann R. 
Published: July 2007

AbstractResults are given of systematic microwave absorption measurements at 35 and 70 GHz in semimetallic BiSb alloys. The great number of experiments permits to made representative statements on the dependence of the cyclotron masses and the relaxation times of the charge carriers from the Sb concentration. Measurements of the electron‐hole hybrid‐resonance field strengths vs. the antimony concentration (x at% of Sb) show that the band parameters of the holes at T do not substantially vary for x < 6.
The Influence of Acoustic Phonon Disturbances on the Conductivity of Piezo‐Electric Semiconductors
Authors: Kocevar P. , Fitz E. 
Published: July 2007

AbstractA closed expression is given for mutual electron‐phonon drag and heating corrections to the steady‐state mobility of weakly drifting non‐degenerate carriers in a polar extrinsic semiconductor of standard band structure with dominant piezo‐electric, acoustic deformation potential, and ionized impurity scattering. The approximations involved are discussed and their range of validity is explicitly stated in terms of electron‐phonon coupling constants, non‐electronic phonon relaxation times, carrier concentration, and lattice temperature. A detailed analysis of n‐GaAs yields corrections of up to 15% to the ohmic conductivity for moderate doping and for lattice temperatures around 20 K. Corrections of more than 20% can only be expected for the non‐ohmic (hotelectron) regime and lattice temperatures below 20 K.
Paramagnetic Resonance and Thermoluminescence of the PbWO4/PbMoO4 Mixed Crystal System
Authors: Hofstaetter A. , Oeder R. , Scharmann A. , Schwabe D. , Vitt B. 
Published: July 2007

AbstractAfter X‐ray excitation of PbWO4/PbMoO4 mixed single crystals at liquid nitrogen temperature two types of MoO ‐electron centres are observed by means of EPR. For low molybdenum concentration axial S4‐symmetry centres are present, whereas in the case of crystals with high molybdenum content the centres undergo a small non‐axial symmetry distortion. The thermal decay of the MoO ‐centres, which contributes to the thermoluminescence emission of the crystals, is discussed with respect to its concentration dependence.
Comparison of Additional Boundary Conditions Based on Thermoreflectance Spectra of the An=1‐Exciton in CdS Crystals at Oblique Incidence
Authors: Stössel W. , Wagner H. J. 
Published: July 2007

AbstractThermoreflectance spectra of the An=1‐exciton in CdS are measured at 8 K for angles of incidence of the light ranging from 5° to 85°, using three different spatial arrangements between the c‐axis, the E‐ and k‐vector of light. Additional boundary conditions of Pekar, Ting et al. and Agarwal et al. are discussed for the first time in terms of optical constants. The refractive indices for these additional boundary conditions are derived, considering special features of CdS, such as optical anisotropy, exciton symmetry, and effective exciton mass anisotropy. Fitting calculations based on the experimental data show that Pekar's additional boundary condition gives the best agreement between theory and experiment.
Stress Dependence of Shallow Acceptor States in Semiconductors with Zincblende Symmetry
Authors: Pertzsch B. , Rössler U. 
Published: July 2007

AbstractThe spherical model for shallow acceptor states in cubic semiconductors is extended to consider the effect of uniaxial stress. The effective‐mass Hamiltonian including stress dependent terms is formulated using spherical tensor operators and dealt with by a variational procedure. By comparing the theoretical results with the donor‐acceptor recombination energy in stressed GaAs: Ge it is shown, that the stress dependence of the shallow acceptor is almost completely determined by the intrinsic properties of the host crystal, which are defined by the effective masses, the band deformation potentials, the spin–orbit splitting, and the dielectric constant.
Electrical Conductivity of Disordered Alloys with Strong Hybridization
Authors: Elk K. , Richter J. , Christoph V. 
Published: July 2007

AbstractThe influence of a strong hybridization on the electrical conductivity σ of disordered substitutional alloys is considered. A remarkable temperature dependence of the conductivity can already arise due to the temperature dependence of the chemical potential and the Fermi distribution function. The temperature coefficient of the conductivity can have both signs in dependence on the band filling. For special values of the electron concentration the temperature dependence of σ may be fairly large and comparable with that one obtained by the electron‐phonon scattering.
Hall Coefficient of Dilute Aluminium Alloys II. Application
Authors: Sato H. , Babauchi T. , Yonemitsu K. 
Published: July 2007

AbstractThe Hall coefficient of Al‐Ag, Al–Ga, and Al–Ge dilute alloys is measured at 4.2, 77, and 293 K as function of the magnetic field strength and solute concentrations. The range of validity of the practical formula given in the preceding paper is investigated for the case of the low field Hall coefficient of dilute alloys at 77 and 293 K.
Energy–Angle Distribution of 14N and 20Ne Ions after Passage through Thin Carbon Foils
Authors: Ellmer K. , Sturm J. 
Published: July 2007

AbstractEnergy–angle distribution of 14 and 20Ne ions penetrating carbon foils with thicknesses from 1.4 to 5.8 μgcm−2 for tilt angles up to 5° are determined. The energy of the incident ions ranged from 19 to 63 ke V (1.34 ≦ ϵ ≦ 7.96). The results are compared with the new theory of Meyer et al. on the energy‐angle distribution of heavy particles penetrating solids. Agreement is found for the angular dependence of the most probable energy loss, wheres pronounced deviations occur for the energy halfwidths‐angular dependence. An attempt is made to explain this discrepancy.
On the Theory of Light Propagation through Disordered Solids. Scattering from Configurational Fluctuations
Authors: Enderlein R. 
Published: July 2007

AbstractThe propagation of light through disordered solids is studied from a general point of view. It is shown that the total scattered light consists of two parts corresponding to phase space fluctuations and configurational fluctuations of the electromagnetic field. A general microscopic expression for the differential cross‐section of scattering from configurational fluctuations is obtained. The theory is applied to a free electron gas with fluctuating density and a non‐interacting system of polarization oscillators with fluctuating resonance frequency.
Luminescence from rare‐gas‐doped solid neon
Authors: Schuberth E. , Creuzburg M. 
Published: July 2007

AbstractThe luminescence in the vacuum‐UV from bulk polycrystals of Ne doped with Ar, Kr, and Xe is investigated. The exciting X‐rays produce free Ne host excitons which relax to their luminescing states. The guest atoms in the Ne matrix are excited, both by the free and by the relaxed excitons. The luminescence of the rare gas dopant atoms consisted of bands whose number, energies, and relative intensities are found not to change with any experimental parameter, in contrast to previous results. These luminescence bands are qualitatively explained to be due to atoms in a perturbing surrounding. Already at concentrations as low as 10 ppm, dimer formation is indicated by efficient luminescence from diatomic dopant molecules. All other observed luminescence is due to small contaminations of the supply gas and is found to be mainly due to oxygen and nitrogen.
Interatomic potentials for alkali metals. A comparative study
Authors: van Heugten W. F. W. M. , De Hosson J. Th. M. 
Published: July 2007

AbstractA comparative study of interatomic potentials for alkali metals is presented. Both, the interaction functions which are derived from phonon‐dispersion curves and Heine‐Abarenkov‐Shaw optimized model potentials are given. For comparison with experimental data some defect calculations are made to obtain the vacancy formation and migration energies in Li, Na, K, and Rb.
Electron beam excited free exciton luminescence of GaSe
Authors: Schwabe R. , Thuselt F. , Hänsel T. , Lévy F. 
Published: July 2007

AbstractOn the layered semiconductor GaSe low temperature cathodoluminescence experiments are performed. Both, the temperature dependence of the free exciton luminescence and kinetical considerations lead to the conclusion that the GaSe band structure causes a peculiar temperature dependence of the exciton band population. The latter is established as a balance between recombination, the formation of excitons from holes and direct or indirect electrons, as well as dissociation of excitons.
Ferromagnetic nickel: Self‐consistent calculation of energy bands
Authors: Marschall E. , Bross H. 
Published: July 2007

AbstractGeneralized Wannier functions defined for a complex of bands are used to fit reliably an MAPW band structure of paramagnetic nickel up to about 1.5 Ryd above the Fermi energy. By adding intra‐atomic Coulomb interaction according to Hubbard the Hamiltonian of the ferromagnetic state is constructed and is solved self‐consistently. The exchange splitting is found considerably k‐dependent. In addition, spin–orbit coupling is taken into account.
Residual electrical resistivity of alloys
Authors: Aubauer H. P. 
Published: July 2007

AbstractA general expression is derived for the residual electrical resistivity for alloys with arbitrary gradients of the concentration and the degree of order. It is applied to disordered alloys, to spinodally decomposed ones as well as for two phase structures, taking care of the finiteness of the electron mean free path Λ. In the latter case maxima of the residual resistivity appear, if the precipitate size is of the order of magnitude of the electron mean free path Λ. This agrees well with a very critical experiment, in which one and the same microstructure is analysed with electrons of varying mean free path Λ.
The anomalous Stark shift of the ground state energy of a donor–acceptor pair in an electric field
Authors: Arepev Yu. D. , Oleinik V. P. , Salkov E. A. , Tolpygo K. B. 
Published: July 2007

AbstractPhoton energies emitted from donor–acceptor pairs (DAP) in semiconductors in an electric field are calculated using a variational procedure. The linear combinations of s‐ and p‐type hydrogen‐like functions are used as trial wave functions of the pair. The magnitude of the Stark shift of the DAP ground state energy as a function R (the distance between the donor and acceptor) and θ (the angle between R and electric field direction E) are obtained for different values of E and m/m (m electron effective mass, m the same for a hole). It is shown that at small values of R and cos θ < 0 (R < aB, aB Bohr radius) the Stark shift is positive due to the strong polarization of the electron and hole clouds in the electric field.
Electron–phonon interaction and phonon conductivity of the n‐type semiconductors Mg2Ge and Mg2Sn at low temperatures
Authors: Singh Mahiradhwaj 
Published: July 2007

AbstractIt is shown that the expressions obtained by Singh for the relaxation rates of the resonance scattering of phonons by donor electrons for n‐type zemiconductors in presence of internal static and dynamic strains in the crystal can account very well for phonon‐conductivity results for the n‐type semiconductors Mg2Ge and Mg2Sn at low temperatures.
Raman Study of the Mixed System [(NH4)1−xKx]2 CuCl4 · 2 H2O
Authors: Sahni V. C. , Bansal M. L. 
Published: July 2007

AbstractA Raman scattering study in the mixed crystal system [(NH4)1−xKx]2 CuCl4 · 2 H2O is reported. It is found that this system has a strong Raman‐active B1g mode, which dominantly involves NH4/K translations and shows a two‐mode behaviour. This behaviour is examined on the basis of a variant of the REI model. Frequency variations with concentration, exhibited by other modes are also studied.
The phase diagram of a system with two order parameters. Mott transition and ferromagnetism
Authors: Litvinov V. I. , Baginskii V. M. , Mitrofanov A. A. 
Published: July 2007

AbstractThe phase diagram of the extended Caron‐Pratt model is constructed. Competing order parameters describe ferromagnetic and metal–insulator phase transitions. The possible phases, the incompatibility of the order parameters, and the existence of the tricritical point are determined.
Cross relaxation studies in the Cr3+‐doped magnetically dilute paramagnetic Al2O3–Fe2O3 system. II. Effect of temperature and external magnetic field
Authors: Srivastava J. K. , Dale B. W. 
Published: July 2007

AbstractMössbauer measurements carried out at 4.2 and 300 K in the undoped and Cr3+‐doped paramagnetic Al2O3–0.04 mol% 57Fe2O3 system indicate a temperature independence of Fe3+–Cr3+ cross relaxation process in the diamagnetic Al2O3 lattice. The measurements made in an external magnetic field Hext, of 30 kOe, applied perpendicular to the γ‐ray beam, show that even in the presence of large Hext, Cr3+ ions have appreciable effect on the shapes of Mössbauer spectra.
A macroscopic calculation of the specific heats of a vacancy
Authors: Varotsos P. A. 
Published: July 2007

AbstractThe constant pressure specific heat Δc, associated with the temperature variation of the formation enthalpy of a vacancy, is calculated from macroscopic properties of the solid. A similar calculation of the corresponding “constant volume” specific heat Δc shows that its absolute value is equal to a few tenths of k. The value of Δc is positive whereas that of Δc is negative, in agreement with recent considerations of Gilder and Lazarus.
Temperature anomalies of the magnetic hyperfine field for Sn in metallic ferromagnets and the thermal expansion of the crystal lattice
Authors: Delyagin N. N. , Krylov V. I. , Nesterov V. I. 
Published: July 2007

AbstractGreat temperature “anomalies” of the magnetic hyperfine fields H for Sn impurity atoms in Fe and Co can be completely or partially explained by the thermal expansion of the crystal lattice. Experimental data are interpreted with the help of a simple model which is based on the representation of H as a sum of partial contributions of the opposite sign with the inclusion of the results of measurements of the pressure dependence of H. The radial dependence of partial contributions into H can be examined on the basis of a joint analysis of the data on the temperature and pressure dependences of H. A brief consideration is given to other possible causes of temperature “anomalies” of the hyperfine field for nonmagnetic atoms in metallic ferromagnets.
Temperature dependence of the relaxation time of the holes in bismuth
Authors: Gollnest H.‐J. , Kuka G. , Braune W. , Herrmann R. 
Published: July 2007

AbstractCyclotron resonance experiments are described on Bi single crystals at 35 GHz. The temperature dependence of the linewidth of cyclotron resonance (CR) of the holes is discussed in detail on the basis of a lineshape analysis. At a temperature of about 5 K a peculiarity in the temperature dependence occurs which can be explained on the basis of hole scattering by phonons.
A model for TTF‐TCNQ conductivity
Authors: Benoit C. , Galtier M. , Montaner A. 
Published: July 2007

AbstractThe dc and optical conductivity of TTF‐TCNQ is described by a modd including a collective mode and small polaron hopping. The optical conductivity is expressed in terms of the one phonon density of state. Satisfactory agreement with far infrared reflectivity measurements is obtained.
Elementary excitations in ferrimagnetic and antiquadrupolar biquadratic systems (S = 3/2)
Authors: Blaszczak E. , Westwański B. , Skrobiś K. 
Published: July 2007

AbstractThe diagrammatic methods for the Racah and standard basis operators are applied to the case of two‐sublattice systems with biquadratic interactions and spin S = 3/2. The elementary excitations are calculated in the (1/z)° approximation (z is the number of spins interacting with any given spin) in three phases: antiquadrupolar, ferrimagnetic, and ferromagnetic. In the antiquadrupolar phase there are two doubly degenerate branches of magnons. The spectrum of quadrons coincides with that of magnons. Three branches of magnons and two branches of quadrons are obtained in the ferrimagnetic phase. In the ferromagnetic phase there is one branch of magnons and one of quadrons.
The isotropic limit in anisotropic dislocation theory Green's functions in a crystal containing a dislocation pile‐up
Authors: Solovev V. A. , Zolotarev S. N. 
Published: July 2007

AbstractA simple method is developed which provides the transition from two‐dimensional anisotropic ekpressions of dislocation theory to isotropic ones. Anisotropic expressions are given for the stress and displacement fields near a dislocation pile‐up (martensite crystal, crack, twin, slip band) in the presence of a single dislocation or a line force lying parallel to the pile‐up. By use of the method presented here, the corresponding isotropic formulae are obtained. These expressions are the Green's functions of dislocation theory for crystals containing a pile‐up type of defect.
Second‐order self‐energy for the Anderson model analytical results
Authors: Zieliński J. , Kozarzewski B. 
Published: July 2007

AbstractAn approximate analytical expression for the second‐order‐self energy for the symmetric Anderson Hamiltonian is obtained. It is shown that the results become exact at high temperatures and are very reasonable for the whole range of temperature and energy. This causes that the method can be relatively easily used for higher order terms making the most competent discussion of the Anderson model to be possible.
On the validity of assuming symmetrical laue diffraction conditions in calculations of diffraction contrast
Authors: Sheinin S. S. , Jap B. K. 
Published: July 2007

AbstractThe form of the dynamical theory normally used in calculations of diffraction contrast is based on the assumption of symmetrical Laue diffraction conditions. The results of previous investigations have shown this assumption to be valid for angles between the surface normal and the Brillouin zone boundary of up to 70°. The results presented in this paper show that although this is true for strong‐beam diffraction conditions, the error involved in calculations based on the assumption of symmetrical Laue diffraction conditions increases significantly as the deviation from the Bragg condition of the strong beam increases. In weak‐beam diffraction conditions significant differences between the symmetrical and non‐symmetrical Laue cases are obtained for angles between the surface normal and the zone boundary as small as 30°. This is verified by calculations of both diffracted beam intensities and dislocation profiles.
Necessity of a phase convention for effective g‐factors and role of the g‐factors in the Knight shifts of PbTe
Authors: Leloup J. Y. , Sapoval B. 
Published: July 2007

AbstractIt is shown that the g‐factors which are commonly used to describe the effect of a magnetic field on an electron in a semiconductor are phase‐dependent quantities. This difficulty, which is related to the non‐tensorial nature of the g‐matrix, is fundamental in a Knight shift theory. To solve this problem a phase convention is introduced which allows to define a „standard representation”︁ between Bloch spinors. This representation yields a common language in which the g‐factors are unambiguously defined and permits to assign a physical meaning to the sign of g⟂. The importance of the sign of the g‐factors is examplified by the surprisingly large ratio of the Knight shifts of Pb207 and Te125 in lead telluride.
Photoconduction in single crystals of a pentamethinium cyanine dye
Authors: Hauschildt D. , Fuhs W. , Hesse H.‐J. 
Published: July 2007

AbstractThe photoconductivity of a pentamethinium cyanine dye is studied on different crystal faces for light polarized parallel and perpendicular to the pentamethinium chain. According to the spectral dependence the first step in the photoconduction process is the excitation of singlet excitons. Free carriers are generated in the volume of the crystals. The photocurrent is recombination limited. The photoconductivity is found to be insensitive to irradiation with high doses of high energetic ions.
Cluster approximation for the spectral density of mixed diatomic systems
Authors: Kleinert P. 
Published: July 2007

AbstractThe spectral density of a mixed diatomic linear chain is investigated using the truncated‐T‐matrix approximation of Berk et al. Only the mass disorder is taken into account. If above the maximum host crystal frequency an impurity band exists then there occur remarkable differences between the cluster and CPA spectrum. In this frequency region the cluster results show some fine structures, which are investigated in dependence on the concentration of the impurities and on a short range order parameter, respectively. A not very pronounced fine structure occurs also between the acoustic and optic band if gap modes exist.