bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Nature of the Long‐Range Dislocation Contrast in Electron Transmission Micrographs
Authors: Wilkens M. , Rühle M. , Hässermann F. 
Published: July 2007

AbstractThe background contrast of dislocations is investigated theoretically using modified Bloch waves. As a result it is found that interband scattering can be neglected outside the dark line (width ≦ one extinction distance) of the dislocation image. The contrast outside the dark line is quantitatively explained by “phase contrast” [4]. i.e. exclusively by the movement of the excitation points of the modified Bloch waves on the dispersion branches. It is shown that the asymmetry often observed in the background intensities adjacent to the black line is an intrinsic contrast phenomenon rather than a consequence of stress relaxation at the foil surface.
About the Role of Minority Carriers in the Impurity Conduction of GaSb
Authors: Aliev M. I. , Safaraliev G. I. , Abdinova S. G. 
Published: July 2007

AbstractMeasurements are made of electrical conductivity, Hall coefficient (R), and thermo‐e.m.f. (α) in GaSb crystals doped with Zn and Te over a wide range of concentrations from 80 to 600 °K. In the pure n‐type samples an anomalous temperature dependence of R is observed, which is considered to be due to a higher subband. In compensated p‐type samples the inversion of the signs of R and α occurs at lower temperatures than in pure p‐GaSb. This is explained by the mixed nature of the conductivity. In compensated p‐type and lightly doped n‐type samples the contribution of minority carriers to α and R is more important than in heavily doped n‐type samples. It is supposed that in pure p‐type crystals of GaSb, uncontrolled compensating impurities cause the contribution of minority carriers to R to be large. This decreases the effective value of the Hall coefficient.
On the Relation between Self‐Diffusion, Melting, and Vacancy‐Impurity Binding in Dilute Alloys
Authors: van den Beukel A. 
Published: July 2007

AbstractStarting from the assumption that melting sets in when the coefficient of self‐diffusion reaches a critical value, the binding energies between vacancies and impurities in a number of dilute Al‐alloys are estimated. The agreement with experimental values is good.
Observed Retardation Effects on the Energy of the ω+‐Surface Plasmons in Thin Aluminium Foils
Authors: Swan J. B. , Otto A. , Fellenzer H. 
Published: July 2007

AbstractCharacteristic energy‐loss measurements using thin aluminium foils are reported, which show a decrease in the energy hω of both types of surface plasmons in the forward scattering direction. The observed decrease in the energy of the ω+‐branch supports the dispersion theory of surface plasmons, which predicts that the phase velocity ω/k of both surface plasmon modes is less than c when retardation is taken into account.
The Phosphorescence of Anthracene Single Crystals and its Spectrum
Authors: Müller H. P. , Thoma P. , Vaubel G. 
Published: July 2007

AbstractBy means of a highly sensitive detecting device the radiative transition from the lowest triplet level of anthracene single crystals to the ground level and several of its vibrational levels are observed at 4.2, 77.4, and 293 °K. Most of these vibrational levels correspond to the levels deduced from fluorescence and solid‐solution phosphorescence studies. At 4.2 °K the radiative triplet lifetime is much larger than at 77.4 °K. The dependence of the phosphorescence intensity on the exciting laser intensity and on crystal temperature is studied.
The Influence of Electron‐Trapping Impurity on Defect Creation and Bleaching in KCl Irradiated at 78 °K
Authors: Crawford J. H. , Sibley W. A. , Sonder E. 
Published: July 2007

AbstractThe excitonic mechanism for creation of halogen Frenkel‐type defects in alkali halides predicts an early positive curvature in the defect growth curve. The model also predicts that annihilation of VK‐centers by the optical release of electrons from traps would produce Frenkel pairs in the halide sublattice. The first prediction has been checked in KCl: Tl+ and KCl:Pb++ irradiated at 78 °K with 1.7 MeV Van de Graaff electrons, and the second upon ir bleaching of an irradiated Tl+‐doped crystal at 78 °K. If one takes the F‐center concentration as a measure of the Frenkel‐defect density, both tests were positive. A careful monitoring of the α‐band region before and after bleaching, however, indicates that the F‐center concentration is not a valid measure of the vacancy density. In a crystal containing 48 ppm Tl°, the α‐center concentration after irradiation at 80 °K was 2.5 times that for F‐centers. Moreover, ir bleaching of Tl° and VK, while enhancing the F‐band ≈ 30%, destroyed nearly all of the α‐centers. The last observation reveals that more empty halide vacancies are destroyed than F‐centers are produced by the bleaching light.
Untersuchung des Jahn‐Teller‐Effektes an Ionen mit Spin 1
Authors: Böttger H. 
Published: July 2007

AbstractDie Linienform der ESR‐Absorption von Ionen mit effektivem Spin S = 1 auf kubischem Gitterplatz wird bei Berücksichtigung der Spin‐Phonon‐Wechselwirkung mit einer Diagrammtechnik berechnet. Es zeigt sich, daß eine in den Phononen lineare Spin‐Phonon‐Wechselwirkung keine Aufspaltung der Absorptionslinie hervorruft, wenn Diagramme zweiter Ordnung berücksichtigt werden.
Entropy and Susceptibility of a Pure Dipole‐Dipole Substance
Authors: Peverley J. R. , Meijer P. H. E. 
Published: July 2007

AbstractRecalculation of the lattice sums for a pure dipole‐dipole interaction show that the Curie‐Weiss constant, for fields perpendicular to the c‐axis is equal to 0.273 mdeg for cerous magnesium nitrate. A g‐value of 1.82 was used. The temperature dependence of the entropy was determined and is compared with the experimental values of Hudson and Kaeser. All lattice sums have been determined as a function of slight changes in the lattice constants. The z‐component of the dipolar lattice sum is determined by means of a new procedure to improve the slow convergence of this series.
Partical Account of Interelectron Correlation in the Theory of Band Structure of Crystals with Sphalerite and Diamond Lattices
Authors: Lyapin V. G. , Tolpygo K. B. 
Published: July 2007

AbstractThe many‐electron theory of the valence band structure in diamond‐like and sphaleritetype crystals, developed in [4, 5], is discussed with reference to Löwdin's AMO method. The one‐electron orbitals appearing in [4, 5] are shown to be equivalent to the functions used in the refined many‐parameter AMO method. The present treatment of the state of a crystal containing a hole includes consideration of the correlation between the two electrons with opposite spins which form a valence bond. Thus, the many‐electron approach makes the approximation used more flexible, and gives a more accurate value of the hole energy E(k) than the one‐electron theories [2]. It also leads to eight twofold spin‐degenerate valence bands (neglecting the spin‐orbit interaction) as opposed to four valence bands in [2]. The “additional” valence bands seem to display themselves in X‐ray emission spectra of the crystals considered.
The Influence of Localized and Resonance Modes of Lattice Vibrations on the Radiative Recombination in Semiconductors
Authors: Ipatova I. P. , Klochichin A. A. , Subashiev A. V. 
Published: July 2007

AbstractThe contribution of localized or resonance modes to impurity induced radiative recombination in semiconductors is considered. The temperature and frequency dependences of the corresponding spectral density are found.
Thermoelectric Power in Amorphous Silicon
Authors: Grigorovici R. , Croitoru N. , Dévényi A. 
Published: July 2007

AbstractAn investigation is made of the temperature dependence of the Seebeck coefficient of vacuum‐deposited amorphous silicon (a‐Si) layers. The temperature dependence of the Fermi level is found to be in good agreement with previous studies of the temperature dependence of the electrical conductivity and the rectifying properties of n‐Si/a‐Si heterojunctions. The present results for a‐Si are compared with those for crystalline Si and crystalline and amorphous Ge.
Aufspaltung der ESR‐Linie durch Spin‐Phonon‐Wechselwirkung an Ionen mit Spin 1
Authors: Böttger H. 
Published: July 2007

AbstractEs wird der Einfluß der Spin‐Phonon‐Wechselwirkung auf das ESR‐Spektrum para‐magnetischer Ionen. mit effektivem Spin S = 1 auf kubischem Gitterplatz untersucht und gezeigt, daß eine in den Phononenoperatoren bilineare Spin‐Phonon‐Wechselwirkung eine Linienaufspaltung bewirken kann. Eine quantitative Abschätzung ergibt für Ni++ in MgO, daß an diesem System eine Linienaufspaltung zu erwarten ist.
Lattice Vibrational Properties of Trigonal Selenium
Authors: Geick R. , Schröder U. , Stuke J. 
Published: July 2007

AbstractThe reflectivity and transmission of trigonal selenium single crystals are studied in the far infrared spectral region. The eigenfrequencies, oscillator strengths, and related quantities of the infrared‐active lattice vibrations are deduced from the reflectivity by means of a classical oscillator model and also from the absorption spectra. The phonon spectra of Se are calculated using a simple force constant model. The calculated phonon frequencies reproduce all the available experimental data within an accuracy of about 10%.
Study of Erbium Thin Film Oxidation in the Electron Microscope
Authors: Murr L. E. 
Published: July 2007

AbstractThis paper describes the formation of suspect ErO single crystals during erbium evaporation onto NaCl in ultrahigh vacuum (10−8 Torr); and a unique twinning phenomenon in these f.c.c. NaCl‐type crystals (a = 5.12 Å) is observed by electron microscopy. The oxidation of thin erbium foils (650 Å thickness) directly within the electron microscope by double condenser beam heating of selected areas and the sequential recrystallization and growth of the completely oxidized erbium (Er2O3) are investigated. It is shown that the Er2O3 films have a b.c.c. structural characteristic with the unit cell defined by a vacancy defect CaF2 structure composition possessing the T5 (I213) space group for a = 10.55 Å. Er oxidation in the electron microscope at a background pressure of roughly 10−4 Torr appeared to be logarithmic, and presumably lattice diffusion controlled.
Der Gitterwärmewiderstand durch Versetzungen in Legierungen bei tiefen Temperaturen
Authors: Zeyfang R. 
Published: July 2007

AbstractEinkristalle aus Cu + 4,6 At% Ga und Ni + 60 At% Co wurden bei verschiedenen Temperaturen (4 bis 293 °K) stufenweise im Zugversuch verformt, nach jedem Verformungsintervall wurde der Gitteranteil der Wärmeleitfähigkeit χg im Temperaturbereich von 1,3 bis 25 °K bestimmt. χg nimmt mit zunehmender Fließspannung wegen der damit verbundenen Zunahme der Versetzungsdichte ab. Bei schwach verformten Kristallen (Bereich I der Verfestigungskurve) gilt zwischen 1,3 und 10 °K χg ˜ T2. Bei hohen Verformungsgraden (Bereich II und III) treten Abweichungen von dieser Beziehung auf; χg steigt bei sehr tiefen Temperaturen stärker als mit T2 an. Die Ergebnisse werden theoretisch durch Abweichungen der Versetzungsanordnung von der statistischen Verteilung gedeutet.
The Néel Temperatures and Stability of Magnetic Phases in the Disturbed Body‐Centered Tetragonal Lattice. Uranium Compounds
Authors: Przystawa J. 
Published: July 2007

AbstractThe RPA Green's function method is used to treat the stability of various antiferromagnetic structures, as observed in a number of uranium compounds, on the basis of Heisenberg exchange interactions between first, second, and third‐neighbours. It is shown that these interactions cannot be neglected in a disturbed body centered tetragonal lattice. Expressions for the Néel temperatures are given and calculated explicitly. These results are compared with molecular field theory and it is shown that the latter correctly determines the range of exchange parameters which is admissible for the stable phase.
On the Thermodynamics of Thermal Diffusion in Substitutional Alloys
Authors: Heitkamp D. 
Published: July 2007

AbstractMass transport by a vacancy mechanism in alloys under a temperature gradient is discussed from the standpoint of non‐equilibrium thermodynamics considering also configurational differences in the chemical potential of the vacancies in an AB‐type alloy. From this point of view it appears insufficient for the derivation of the transport equations to define a mean formation enthalpy of all vacancies of an alloy over the whole concentration range. An approximation is proposed formally distinguishing between the formation enthalpy of vacancies which change their sites with A‐atoms and that of vacancies which interchange with B‐atoms. The difference between these formation enthalpies is especially significant for dilute alloys.
Contribution á l'étude des phénomènes de transport dans les structures aluminium–alumine–métal
Authors: Rouzeyre M. 
Published: July 2007

AbstractNous décrivons plusieurs expériences sur l'effet photoélectrique interne dans les structures aluminium‐alumine‐métal qui permettent de rejetter l'hypothèse d'une faible longueur d'atténuation en énergie des électrons dans l'alumine. L'interprétation à partir des propriétés des électrodes permet d'expliquer simplement un certain nombre de phéno‐mènes qui ne peuvent être traduits par un modèle de conductivité et d'atteindre directement la longueur d'atténuation en énergie des électrons dans l'aluminium par de simples mesures de tension. Cette longueur d'atténuation varie entre 6 et 18 Å dans le domaine d'énergies eonsidéré et croît sensiblement com me le carré de la longueur d'onde de la lumière excitatrice. En supposant l'existence de deux types d'interactions dans l'alumine, les unes élastiques, les autres inélastiques, on peut aussi évaluer l'ordre de grandeur de la longueur d'atténuation en énergie correspondent, à ces dernières.
Theoretical Studies on Z1‐Bands in Alkali Halide Crystals
Authors: Cheung T. H. , Wang S. 
Published: July 2007

AbstractThe absorption energies and the oscillator strengths of Z1‐bands in the calcium doped crystals are theoretically investigated. The calculation is done by using both the polaron model of electron‐excess centers and the valence‐electron models of atom. The numerical results are given for both the substitutional model and the Bushnell model. These results give an additional support to the general suggestion of Bushnell and lead to the conclusion that the Z1‐band may be considered as the F‐band perturbed by the complex consisting of a positive‐ion vacancy and a divalent impurity.
Statistical Perturbation Theory of Order–Disorder Ferroelectrics: Zeroth Approximation
Authors: Nettleton R. E. 
Published: July 2007

AbstractApproximate spin‐wave energies are calculated by constructing approximate eigenvalues of the commutator operator [H, ]. One linearizes commutators by replacing the Z spin operator by its expectation 〈Z〉 and then determines the latter self‐consistently. Such a calculation is discussed for the Blinc formulation of the Slater‐Takagi‐Senko model of KH2PO4 which is treated by a coordinate rotation similar to that used by DeGennes. For sufficiently large tunneling of protons on hydrogen bonds, the rotation angle will approach π/2 at a temperature defining a second‐order transition. If tunneling is weak, the transition is first‐order, unless there is no tunneling. In the latter case, the model reduces to that of the Weiss molecular field, and the transition is again of second order.
Diffusion of Tl+ in Doped and Pretreated KCl
Authors: Glasner A. , Reisfeld R. , Linenbebg A. 
Published: July 2007

AbstractThe diffusion coefficients of Tl+ ions are measured in “pure” KCl crystals (obtained from the melt or crystallized from aqueous solutions), and in KCl crystals doped with SrCl2 or BaCl2, over the temperature range 160 to 210 °C. Doping and various other treatments decrease the diffusion constants compared with those in the melted sample. This is accompanied by a large increase in the apparent jump energy EA. The assumption of metastable supersaturated solutions of the divalent impurity ions present in “pure” KCl leads to a consistent and quantitative interpretation of these results. The jump energy of the Tl+ ions, δhTl, calculated from results for the above KCl samples is found to be (0.84 ± 0.02) eV, whilst a specially purified sample, containing a total divalent impurity concentration cp = 2.17 × 10−6, gives the direct value: δhTl = 0.836 eV. The mean heat of dissolution χi of the prevalent divalent impurities is (1.44 ± 0.04) eV, and the corresponding entropy factor ηi is 0.953 × 10−3 eV/deg. The supersaturation concentration in samples from the melt is found to be about 5 × 10−6 mole fraction.
Slowly Propagating high‐Field Domains in Semiconductors with Negative Differential Conductivity
Authors: Kröll K.‐E. 
Published: July 2007

AbstractSlow high‐field domains which, move without deformation through a semiconductor are discussed. The domain velocity is obtained by various methods: by starting from linearized differential equations, by using the properties of singular points and by numerical calculations. Furthermore, the latter calculations show that slowly moving symmetrical domains are possible. For this special case the system of nonlinear differential equations is solved by using a method due to Volkov.
Magnetic properties of Al‐substituted yttrium orthoferrite
Authors: Wang F. F. Y. , Kestigian M. 
Published: July 2007

AbstractThe 10 mol% Al‐substituted yttrium orthoferrite (YFe0.9Al0.1O3) crystal becomes uniaxially antiferromagnetic at 602 °K. It exhibits weak ferromagnetism at about 600 °K. The magnetization data were used to test the models for the origin of weak ferromagnetism. The antisymmetrical exchange (Dzyaloshinsky‐Moriya) model was found to be a better suited model. Parameters for the model were calculated from the data.
Zur Richtungsdispersion der optischen Gitterschwingungen des tetragonalen BaTiO3 bei Zimmertemperatur
Authors: Merten L. 
Published: July 2007

AbstractDie Gleichung für die Richtungsdisperision der sogenannten außerordentlichen ultrarotaktiven optischen Gitterschwingungen wird für optisch einachsige Kristalle allgemein formuliert. Speziell wird die Richtungsdispersion von sechs der insgesamt sieben richtungsabhängigen Schwingungszweige des tetragonalen BaTiO3 berechnet und diskutiert. Es ergibt sich eine extrem starke Richtungsdispersion der “soft mode” im Winkelbereich von 0° bis etwa 30° des Winkels zwischen Wellenvektor und optischer Achse.
Zur Photoimpedanz von ZnS‐Phosphoren
Authors: Krispin P. 
Published: July 2007

AbstractEs werden die Kapazität und der Verlustfaktor von eingebetteten ZnS‐Phosphoren in Abhängigkeit von der Frequenz des elektrischen Wechselfeldes und der Anregungsintensität gemessen. Bei Leuchtstoffen mit kubischer Kristallstruktur und hinreichend hohem Sauerstoffgehalt tritt ein Verlustfaktormaximum auf, dessen Frequenzlage von der Anregungsintensität unabhängig ist. Dieses Impedanzverhalten kann mit Raumladungsprozessen erklärt werden, wobei die Einstellzeit des quasistationären Gleichgewichts zwischen den Elektronen im Leitungsband und in Störtermen eine Dispersion der Photoimpedanz verursacht. Im Zusammenhang mit den beschriebenen Ergebnissen werden die bisher benutzten Kriterien für das Vorliegen eines echten dielektrischen Effektes analysiert.
Einfluß von Neutronenbestrahlung auf die plastische Verformung von Eisen‐Einkristallen mit unterschiedlichem Kohlenstoffgehalt. I. Die Fließspannung am Verformungsbeginn
Authors: Seidel G. P. 
Published: July 2007

AbstractDer Mechanismus der Bestrahlungsverfestigung von Eisen‐Einkristallen niedrigen Kohlenstoffgehalts (20 bzw. ⪅ 8 Gew.‐ppm) wurde durch Messung der Abhängigkeit der Streckgrenze von der Bestrahlungsdosis und von der Verformungstemperatur sowie durch Anlaßversuche untersucht. Der bestrahlungsinduzierte Streckgrenzenzuwachs hängt sehr stark vom Kohlenstoffgehalt ab, erreicht schon bei niedriger Dosis (3 × 1017 n/cm2) eine vollständige Sättigung und heilt erst oberhalb 230 °C aus. Die Temperaturabhängigkeit der Streckgrenze kann durch die Wechselwirkung der Versetzungen mit Fehlstellen tetragonaler Symmetrie beschrieben werden. Die Ergebnisse werden damit gedeutet, daß durch die Neutronenbestrahlung Versetzungshindernisse in Form von Komplexen aus Kohlenstoffatomen mit Leerstellen oder Zwischengitteratomen entstehen.
The stress dependence of the dislocation velocity in molybdenum
Authors: Guiu F. 
Published: July 2007

AbstractThe exponent m* in the velocity‐stress relation V = (τ*/*0*)m* is calculated from data on the strain rate sensitivity of the flow stress of molybdenum single crystals. The values of m* thus obtained (for different orientations of the crystals) are compared with those determined by other workers from measurements of edge dislocation velocities. Agreement is obtained only if the effective stress acting on the dislocations is assumed to be independent of the temperature. Since no justification can be found for this assumption it is concluded that the parameters m* and τ0* may have different values depending on whether the above equation applies to the mobility of edge or screw dislocations. They may depend also on the mode of deformation, hence on the orientation of the crystals.
Magnetoplasma reflection in mercury telluride
Authors: Śniadower L. , Kowalczyk R. 
Published: July 2007

AbstractA detailed analysis is presented of magnetoplasma reflection in semiconductors. Theoretical curves are given to show the effect of the effective mass m*, the relaxion time τ, and the dielectric constant ϵ on the shape of the plasma edge. A method is given for the simultaneous determination of m*, ϵ, τ and the concentration N on the basis of the experimental variations of reflectivity in the plasma edge region. This is applied to the analysis of result obtained for n‐type HgTe at 296 and 85 °K. An increase of the effective mass and a decrease of the dielectric constant decreasing of temperature are observed.
Electron temperature in polar semiconductors
Authors: Licea I. 
Published: July 2007

AbstractUsing the electron temperature approximation an analysis is made of the scattering integral in an intense electric field for a semiconductor with an arbitrary non‐parabolic energy band. The electron temperature is then derived for a purely polar semiconductor with a non‐parabolic dispersion law such as n‐type InSb. The calculations only include optical phonon scattering and assume that both energy and momentum exchange is controlled by interelectronic collisions. The problem is treated for “warm” and “hot” electrons and a comparison with the parabolic case is made.
Mössbauer investigations of Mg, Mn, and MgMn ferrites in external magnetic fields
Authors: Wieser E. , Povitskii V. A. , Makarov E. F. , Kleinstück K. 
Published: July 2007

AbstractThe Mössbauer spectra of six Mn, MgMn, and Mg ferrites had been measured with a transversal and longitudinal external magnetic field. The line shifts make possible the coordination of the internal fields with octahedral and tetrahedral sites and confirm especially the deviations from the Néel model predicted for the MgMn ferrites. From the polarization effects in the longitudinal field we see that existing deviations from the Néel model could be only in the form of opposite directed spins within the sublattices.