bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Modulation Spectra of Selenium and Their Dependence on the Uniaxial Stress
Authors: Tuomi T. O. 
Published: July 2007

AbstractWavelength‐ and stress‐modulated reflectance and transmission spectra of selenium are measured at 77 °K in the photon energy range from 1.7 to 3.7 eV. New structure is discovered, e.g. a peak at 2.0 eV in the wavelength‐modulated reflectance spectrum with light polarized parallel to the [0001] direction. Unusually large linear stress coefficients of the peaks are found. The stress coefficient of the sharp exciton peak at 1.97 eV in the wavelength‐modulated reflectance spectrum with light polarized perpendicular to [0001] is +(2.5 ± 0.4) × 10−11 eV cm2 dyn−1 for the uniaxial compression along the [0001] direction, and −(6.7 ± 0.5) × 10−11 eV cm2 dyn−1 for the compression along [1000].
Symmetry Properties of the Antiferromagnetic Structure of CuCl2·2H2O
Authors: Joshua S. J. 
Published: July 2007

AbstractNew experimental data [12] have indicated that CuCl2 · 2H2O may be a four sublattice canted antiferromagnet in accordance with Moriya's predictions [17]. However, the data obtained are too few and too weak to confirm Moriya's model. We show by using group theoretical arguments that CuCl2 · 2 H2O has in fact a canted structure with the spins canting in the x‐z plane.
Landau Damping of Magnetoplasma Excitations in Many‐Valley Semiconductors
Authors: Wallace P. R. 
Published: July 2007

AbstractTheoretical calculations are made of the effect of Landau damping and Doppler‐shifted cyclotron damping on the transverse (helicon‐like) and longitudinal (plasma) excitations of a many‐valley semiconductor such as PbTe or Ge in an external magnetic field, in the Faraday configuration. It is shown that Landau damping dominates only for low‐frequency helicon modes. For higher‐frequency modes, Landau damping is present, but generally occurs only in the frequency ranges in which Doppler‐shifted cyclotron damping is already present.
The Fine Structure of Spots in Electron Diffraction Resulting from the Presence of Planar Interfaces and Dislocations. V. Observations on Coherent Domain Boundaries
Authors: de Ridder R. , van Landuyt J. , Gevers R. , Amelinckx S. 
Published: July 2007

AbstractObservations of the fine structure of electron diffraction spots due to the presence of coherent domain boundaries in ordered Ni4Mo are compared with theoretical results derived in part III of this paper. It is shown that the predicted fine structure consisting of satellites lying in a direction perpendicular to the image fringes can be observed. How‐ever, in general, only one or two out of the four predicted satellites are registered, the intensity of the other ones being too small. Analysis is made of the fine structure and excellent agreement between theory and experiment is found. Identification of the satellites, based among others on intensity considerations is possible and illustrated on an example. Moreover, the orientation parameters such as s, Δs, and the extinction distance can be estimated from the geometry and a method is outlined allowing to calculate the absorption length from the measured intensities of the satellites.
Interatomic Interactions in Alkali Halides
Authors: Abarenkov I. V. , Antonova I. M. 
Published: July 2007

AbstractUsing free ion orbitals two‐body and three‐body potentials between nearest and next‐nearest neighbours in several alkali halides have been calculated. The two‐body potentials have been calculated without any expansion in power‐series of overlap integral S. The three‐body potentials have been calculated approximately, only terms of the order S2 being retained. The results show that the use of the free ion orbitals leads to somewhat too strong repulsion between the ions.
Ionized Impurity Scattering in Polar Semiconductors at Strong Electric Fields
Authors: Licea I. 
Published: July 2007

AbstractIonized impurity scattering processes by a strong electric field in semiconductors with an arbitrary non‐parabolicity of spherical‐symmetric conduction band are considered in the electron temperature approximation. Using the energy and momentum conservation equations, established for this case, the warm electron temperature and mobility in a polar semiconductor with a non‐parabolic energy dispersion law as that of n‐type InSb are studied. The effect of non‐parabolicity is pointed out and a comparison with the parabolic case is made.
Current Transients in the Insulator Determined by Space Charge and Diffusion
Authors: Rosental A. , Lember L. 
Published: July 2007

AbstractThe mathematical problem of one‐carrier space‐charge‐limited current (SCLC) step‐response in a perfect insulator is solved with a digital computer taking carrier diffusion into account. Curves of forward‐current density vs. time are presented with an error analysis and a brief discussion of the parameter influence for the case of a dielectric diode under different values of applied pulse voltages in the steady‐state current range where a square‐law behaviour begins to show up and inclusion of diffusion in the treatment is indispensable. The lowering of the voltage in this range deprives gradually the mean features of the SCLC transient ascertained for the diffusion‐neglected case. Last of all only the diffusion‐dominated current in the very beginning of the transients remains. The maximum time for observing the diffusion contribution to the pulse current estimated by Schilling and Schachter proves to be understated.
Thermal Expansion Coefficient and Grüneisen Parameter of Na and K Based on Toya's Electron—Phonon Interaction
Authors: Srivastava R. S. , Singh K. 
Published: July 2007

AbstractPhonon dispersion relation derived by Toya and based on the Hartree‐Fock method has been used for computation of phonon frequencies, Grüneisen parameter, and thermal expansion coefficients for sodium and potassium. The Brillouin zone was divided into 1000 miniature cells. Phonon frequencies and Grüneisen parameter corresponding to the centre of the miniature cells were computed and used for studying the variation of γM — the mean value of the Grüneisen parameter — with temperature. Variation of the thermal expansion coefficient with temperature was also studied in the manner of Wallace. It is found that the pseudopotential approach by Wallace gives practically the same results as Toya's theory, at least so far the variation of the thermal expansion curve is concerned. Similar calculations have been done by Buyers and Cowley on the basis of anharmonic effects.
On the Theory of Hot Luminescence and Resonant Raman Effect of Impurity Centres
Authors: Hizhnyakov V. , Tehver I. 
Published: July 2007

AbstractFor an impurity centre the resonant secondary radiation spectrum, consisting of luminescence, Raman scattering, hot luminescence, and interference terms, is studied at low temperatures using the model of one local or pseudolocal mode, active in the electronic transition and taking into account the change of the equilibrium position and frequency of this mode. It is shown that the latter plays an essential role in the problem of the classification of the resonant Raman scattering and hot luminescence. The anti‐Stokes region of the spectrum is analysed in detail for three cases of excitation: monochromatic, “white”, and intermediate excitation. The influence of the interference of different relaxation channels on the intensity, width, and shape of the lines is considered.
Hall Mobility of Electrons in Anthracene Crystals
Authors: Schadt M. , Williams D. F. 
Published: July 2007

AbstractThe Hall mobility for electrons has been measured in anthracene along different crystallographic axes. The electrons were injected into the crystals with solid electrodes containing anthracene negative ions (Na‐anthracene). To avoid any magnetic effects arising from photoconductivity, all experiments were performed in the dark and great care was taken to avoid double injection. The Hall mobilities for electrons at room temperature are ≈ 9 cm2 V−1s−1 (a‐axes), ≈ 7 cm2V−1s−1 (b‐axes), and < 2 cm2V−1s−1 (c′‐axes; no sign could be determined). The anomalous Hall mobilities predicted by the narrow band description of carrier transport in anthracene were not found.
Pair Formation and Tetrahedral Coordination of Co2+ in AgCl and AgBr
Authors: Koswig H. D. , Ulrici W. 
Published: July 2007

AbstractThe analysis of the optical absorption spectra (measured at 20 °K) of Co‐doped (< 800 ppm), quenched AgCl and AgBr crystals shows that in addition to octahedrally coordinated Co2+ (incorporated on cation sites) there are also tetrahedrally coordinated Co2+ ions. Tetrahedrally coordinated Co2+ arises from pairs of Co2+ ions on cation sites in which one of both Co2+ jumps on an interstitial site when both the charge compensating cation vacancies are situated in the neighbourhood of the pair. The concentration of pairs is determined by the probability to find a Co2+ ion in the neighbourhood of another one. In Co‐doped crystals additionally doped with other divalent cations the Co2+ ion jumps on an interstitial site also in that pairs in which the second cation is not Co2+. This leads to an enhancement of the concentration of tetrahedral Co2+ centres related to crystals without additional doping. The investigation of this enhancement as a function of the cation concentrations provides the spatial arrangements of the cations in the pair leading to tetrahedral Co2+ centres in the different cases.
Hot Electron Magnetoconductivity in Polar Semiconductors
Authors: Licea I. 
Published: July 2007

AbstractAn investigation is made of the magneto‐conductivity of hot electrons in polar semiconductors with an arbitrary non‐parabolicity of the spherically symmetric conduction band in the electron temperature approximation. Basing on these results the Hall effect, the relative resistivity change, and the Hall velocity in a polar semiconductor with a non‐parabolic energy dispersion law like that of n‐type InSb are studied theoretically considering only optical polar scattering and treating comparatively both non‐parabolic and parabolic cases.
Bulk Negative Differential Conductivity in Stressed n‐Type Germanium
Authors: Chattopadhyay D. , Nag B. R. 
Published: July 2007

AbstractThe velocity‐field characteristics of stressed n‐type germanium at 300 °K have been theoretically obtained assuming a Maxwellian velocity distribution function. It is found that the experimentally observed bulk negative differential conductivity cannot be explained if the carriers are assumed to be confined to the 〈111〉 valleys only. The experimental results on the other hand may be fitted if carrier scattering to the 〈100〉 valleys is taken into account and the mobility of the carriers in these valleys is taken to be 690 cm2 V−1 s−1.
Induced Anisotropy in Coarse‐Grained and Single Crystalline Samples
Authors: Lesnik A. G. 
Published: July 2007

AbstractThe formation mechanism of induced anisotropy described in [1] is applied to coarse‐grained and single‐crystalline samples. In this case the anisotropy is explained by an inhomogeneous distribution of vacancies and foreign atoms along the block boundaries or by their piling up along the antiphase boundaries in an ordered alloy.
Theory of Optical Absorption by Diatomic Molecules Embedded in Rare Gas Crystals
Authors: Mannheim P. D. , Friedmann H. 
Published: July 2007

AbstractA new mechanism for the study of lattice dynamics is presented, rotation‐translation coupling. With this mechanism the optically active rotational modes of diatomic molecules are coupled to the lattice vibrations of crystals in which the diatomic molecules are embedded. Using recently derived expressions which incorporate force constant changes in the vicinity of the defect we calculate and identify localized modes seen in the IR spectrum of HCl and HBr in rare gas crystals. Further we show how the lattice vibrations shift and broaden the rotational levels of the molecule. It is thought that this mechanism will prove useful in the study of the density of states of pure and impure crystals.
Magnetophonon Resonance in Tellurium
Authors: Bresler M. S. , Mashovets D. V. 
Published: July 2007

AbstractAn investigation was made of the magnetoresistance of tellurium single‐crystal samples in magnetic fields up to 400 kOe at liquid nitrogen temperatures for different relative orientations of magnetic field, sample current, and crystal threefold axis. For the interpretation of the observed magnetophonon resonance oscillations the system of Landau levels for the tellurium valence band is calculated in the quasi‐classical approximation taking into account the phenomena related to the presence of a saddle point in the band energy spectrum (intraband magnetic breakdown). The long‐wavelength optical vibrations in the tellurium lattice are discussed. It is suggested that from three optical phonon modes inducing the first‐order dipole moments one mode predominates in carrier scattering. The calculated positions of the magnetophonon oscillations are in good agreement with the experiment.
Theory of Electron Scattering from an Antiferromagnet. II. Itinerant Model
Authors: Falicov L. M. , De Wames R. E. 
Published: July 2007

AbstractThe theory of electron scattering by an antiferromagnet is extended to include the case of metallic targets, in which the periodicity of the magnetic arrangement is not necessarily commensurate with the lattice. In the Hartree‐Fock (random phase) approximation, it is shown that the elastic part of the differential scattering cross section has an expression equivalent to that derived for the Heisenberg model in an antiferromagnetic insulator, with the difference that the sublattice magnetization is replaced by the proper Fourier component of the oscillatory magnetization.
A Green's Function Approach to Intermediate‐ and Strong‐Coupling Polaron Theory in the Presence of External Fields
Authors: Porsch M. 
Published: July 2007

AbstractA general method for studying the properties of free and bound polarons at arbitrary strength of electron‐phonon coupling is given from a unified point of view by first performing a suitable canonical transformation of the electron and phonon field operators and subsequently applying the double‐time Green's function formalism to the transformed polaron‐phonon Hamiltonian. Calculating the one‐polaron Green's function in the lowest approximation and employing the variational principle for the free energy, a pair of coupled differential equations is derived for the effective wave function and a trial function as introduced by the canonical transformation. From these equations, the weakly excited polaron energy levels at low temperatures can be found in the entire range of coupling constants when external fields are present. In this paper, detailed calculations are confined to the optical‐polaron problem in the zero‐field case. Intermediate‐ and strong‐coupling formulas for temperature‐dependent polaron self‐energy and effective mass are given. The strong‐coupling regime appears to increase with temperature.
Peierls Energies of Dislocations on {110} Glide Planes in the B.C.C. Lattice
Authors: Heinrich K. , Schellenberger W. , Pegel B. 
Published: July 2007

AbstractThe Peierls potentials of different types of crystallographic dislocations moving on {110} glide planes are computed by means of various models and a systematic study of a 35° dislocation is carried out for different model series. It is shown that the original Peierls model can lead to qualitative errors concerning the structure of the Peierls potential and yields too small dislocation widths.
Spin Wave Modifications in Ferromagnetic Alloys by Spherical Island Structures
Authors: Heiner E. , Elk K. 
Published: July 2007

AbstractThe change of the spin wave spectrum of a ferromagnetic alloy by spherical inclusions of a second ferromagnetic phase is determined in a semiclassical approximation. Inside the spherical islands resonances are obtained in dependence of the quotient of the stiffness constants and spin wave damping. The damping is described by the imaginary part of a complex potential.
Einfluß von Fremdmetalldotierung auf die galvanomagnetischen Effekte von Kadmiumeinkristallen bei tiefen Temperaturen
Authors: Schwarz H. 
Published: July 2007

AbstractAn Kadmium‐Einkristallen, die jeweils verschieden stark mit Zink, Quecksilber oder Silber dotiert waren, wurde die Orientierungsabhängigkeit des Halleffektes und des elektrischen Widerstandes im Magnetfeld bei 4,2 °K gemessen. Die Widerstandsverhältnisse der Proben lagen zwischen 13000 und 300. Bei beiden Effekten treten Abweichungen von der Kohlerregel auf, die beim Halleffekt besonders stark ausgeprägt sind. Die unterschiedlichen Ergebnisse des Hallkoeffizienten der einzelnen Kristalle lassen sich deuten, wenn man annimmt, daß durch die Verunreinigungen Kleinwinkelstreuung zwischen verschiedenen Teilen der Fermifäche hervorgerufen wird, wodurch der Charakter der Elektronenbahn geändert wird. Die Wahrscheinlichkeit für eine solche Streuung ist von der Art des Zusatz‐metalls abhängig.
Transmission Electron Microscopy of Point‐Defect Clusters in Neutron‐Irradiated Metals. II. Platinum
Authors: Rühle M. , Häussermann F. , Rapp M. 
Published: July 2007

AbstractAnnealed, neutron‐irradiated, and neutron‐irradiated and subsequently annealed platinum has been investigated by means of transmission electron microscopy. In as‐annealed platinum black dots were observed; these defects occurred only near the foil surfaces and were similar to the polishing defects in copper [8]. Frank dislocation loops, prismatic dislocation loops, and voids were found in neutron‐irradiated foils. After annealing for 1 h at 543 °K the same defect types were observed, however, the contrasts of the defects were stronger. The results are compared with those of other authors.
Isotope Effect for Self‐Diffusion in Single Crystals of Silver
Authors: Rothman S. J. , Peterson N. L. , Robinson J. T. 
Published: July 2007

AbstractThe simultaneous diffusion of 105Ag and 110Ag in silver single crystals has been measured over the temperature range 640 to 955 °C. The strength of the isotope effect has a constant value of 0.718 ± 0.011 for T < 750 °C, but decreases with further increases in temperature to a value of 0.639 ± 0.013 at 937 °C. This temperature dependence is significant at the 90% confidence level. Although one may explain the observed decrease by the temperature dependence of ΔK, we consider it more likely that the decrease results from the simultaneous operation of vacancy and divacancy mechanisms. At the melting point, the contribution of divacancies is from 11 to 45% of the total self‐diffusivity. The diffusion coefficient of 110Ag in Ag single crystals over the same temperature range was also obtained from these experiments. The least squares Arrhenius line is described by D0 = 0.67 cm2/s, Q = (45.2 ± 0.2) kcal/mol ( = (1.97 ± 0.1) eV). The values of D deviate systematically from this line in the manner expected for simultaneous vacancy and divacancy diffusion, although the statistical significance of these deviations is not certain.
Thermodynamic Equations for Dysprosium‐Aluminum Garnet near Its Néel Point
Authors: Bartis F. J. 
Published: July 2007

AbstractA thermodynamic argument is used to derive equations describing a cubic antiferro‐magnet during a stress‐broadened first‐order phase transition. A linear relation between the heat capacity and the thermal expansivity of dysprosium‐aluminum garnet is found to be consistent with the present results as well as those obtained by Janovec for a lambda‐transition. It is concluded that agreement with an equation of this type is not sufficient to determine the nature of a phase transition.
Atomic Distribution and Magnetic Moment in Liquid Iron by Neutron Diffraction
Authors: Waseda Y. , Suzuki K. 
Published: July 2007

AbstractThe structure of iron in the liquid state has been studied by neutron diffraction at 1620 °C. After calculation of the interference function (Fourier analysis), the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. The value of the magnetic moment of iron in the liquid state which was derived from the correction for the paramagnetic neutron scattering was 1.2 μB.
Radiative Electron Capture by Gold and Platinum Impurities in Germanium
Authors: Slatter J. A. G. 
Published: July 2007

AbstractIt is shown that when negatively charged gold and platinum impurities in germanium capture thermal electrons into levels lying 0.2 eV below the conduction band, the probability of photon emission varies from 10−3 to 10−5 for the gold impurities, and from 10−5 to 10−7 for the platinum impurities, as the lattice temperature changes from 35 to 85 °K. These results were obtained with the use of an expression, derived from the principle of detailed balance, that relates the probability of a capture event being radiative to photoconductivity per unit intensity of illumination.
Theoretical Determination of the Second‐Order Elastic Constants of NaCl‐Type Alkali Halides
Authors: Szomor P. O. 
Published: July 2007

AbstractThe second‐order elastic constants of NaCl‐type alkali halides were calculated on the basis of Hooke's law. The calculations were performed using the Born‐Mayer model for the lattice energy of ionic solids. The results obtained show that contrary to expectations the Cauchy relations are not fulfilled.
On Elastic Properties of Covalent Crystals
Authors: Vukcevich M. R. 
Published: July 2007

AbstractElastic properties of cubic, covalently bonded, monoatomic solids are discussed in terms of a new model based on a general expression for the potential energy which is a function of the interatomic distances and angles between the bonding electronic orbitals. Earlier theories are based on parametric expressions for forces, and cannot be used to obtain any additional information. The energy method used here is as general as the classical central force model. Hooke's law for high pressures is derived and effective elastic constants and their pressure derivatives are formulated. Diamond is used as a model solid, and encouraging agreement was found between the theoretical predictions and measured values of the second‐order elastic constants and the Grüneisen parameter.
Electric Field Dependent Plasma Oscillations in Semiconductors
Authors: Krishnamurthy B. S. , Paranjape V. V. 
Published: July 2007

AbstractThe direct effect of the electric field on the electron plasma dispersion relation in semiconductors with simple parabolic band model is investigated by the kinetic method. A model distribution function has been invoked which takes into account the fluctuation in density and momentum of electrons. The possibility of amplification or attenuation of the plasma excitation is discussed.
The Quasi‐Pauli Representation of Spin Operators
Authors: Žakula R. B. , Lalović D. I. 
Published: July 2007

AbstractA quasi‐Pauli representation of the spin operators is given. Since there are exact methods of representing the quasi‐Pauli operators by either Bose or Fermi operators, this enables an analysis of the processes in ferromagnets and antiferromagnets to be performed in a more completed way.
Mössbauer Effect in Nickel‐Rich Nickel‐Manganese Alloys
Authors: Chandra G. , Radhakrishnan T. S. 
Published: July 2007

AbstractNickel‐rich nickel‐manganese alloys with manganese concentrations of 2, 4, and 16 at% have been investigated at various temperatures by Mössbauer spectroscopy using Fe57 as the probe nucleus. The sample with 16 at% Mn concentration has been studied in detail for various heat treatments. For all heat treatments it shows anomalous spectra consisting of an intense central line together with a magnetic structure, over a wide range of temperatures. Three different possibilities have been considered to account for the anomalous spectra. They are the co‐existence of two phases corresponding to long‐range order and short‐range order, the co‐existence of nickel‐rich and manganese‐rich regions, and relaxation effects.