bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Measurements 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.
Magnetic Properties of PbTe
Authors: Akimenko N. I. , Staryk P. M. , Tovstyuk K. D.
Published: July 2007

A study is made of the magnetic susceptibility and Hall effect in PbTe. The experimental results are in good agreement with the theory for nonparabolic bands.
On the Relation between Self‐Diffusion, Melting, and Vacancy‐Impurity Binding in Dilute Alloys
Authors: van den Beukel A.
Published: July 2007

Starting 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

Characteristic 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

By 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

The 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

Die 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

Recalculation 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

The 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

The 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

An 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.
The Nonlinear Excitation of Strongly Coupled Spin Waves
Authors: Loos J.
Published: July 2007

The nonlinear excitation of linearly coupled spin waves is treated using a particular model of coupled oscillators. The results obtained are used to discuss the magnon distribution and the χ″(h) dependence for the ferromagnetic resonance in the presence of strong two‐magnon scattering.
Aufspaltung der ESR‐Linie durch Spin‐Phonon‐Wechselwirkung an Ionen mit Spin 1
Authors: Böttger H.
Published: July 2007

Es 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

The 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

This 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

Einkristalle 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.
Measurement of the Magnitude of the Electronic Attenuation of Sound in Metals
Authors: Jones B. K.
Published: July 2007

A discussion is presented of methods of measuring the total electronic component of the attenuation of sound waves in metals.
The Néel Temperatures and Stability of Magnetic Phases in the Disturbed Body‐Centered Tetragonal Lattice. Uranium Compounds
Authors: Przystawa J.
Published: July 2007

The 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

Mass 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

Nous 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

The 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

Approximate 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

The 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

Slow 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

The 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

Die 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

Es 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

Der 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

The 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

A 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

Using 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

The 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.
The attenuation length of photoelectrons in thin films of uranium
Authors: Lea C. , Mee C. H. B.
Published: July 2007

Films of uranium up to about 1000 Å thick were evaporated on to quartz substrates at pressures less than 5 × 10−10 Torr. The attenuation length L of photoelectrons in the films was estimated by comparing the photoelectric emission current when the film was illuminated from the vacuum side (i1) to that when the film was illuminated from the substrate side (i2). Theory indicates a linear relationship between log (i1/i2) and thickness, and this was confirmed by experiment for illumination with light of photon energies from 3.5 to 5.0 eV. The constants of the relationship yield values for L between 60 and 120 Å, the attenuation length decreasing with increasing photon energy. Measurements of the electrical conductivity of the films as a function of thickness yielded a value for the mean free path of the conduction electrons of about 290 Å. The results suggest that the principal energy‐loss mechanism for the excited electrons is one of electron‐electron scattering.
Photoconductivity of CsBr single crystals containing F ‐ and M‐centres
Authors: Pelsers L. , Jacobs G.
Published: July 2007

The photoconductivity of additively coloured CsBr crystals was measured in function of wavelength and temperature. The temperature dependence of the quantum efficiency for the two main components of the F‐band is found to be identical. A possible explanation is given following Fowler's suggestion about a diffuse relaxed excited state after absorption. When the temperature dependence of the mobility is taken into account and the expression of Swank and Brown for η is used, a theoretical curve of η w as a function of temperature can be fitted to the experiment with a thermal ionization energy of 0.065 eV. F‐aggregate centers are formed when the F‐band is optically bleached at _ 100 °C. The temperature behaviour of the photoresponse and the spectral distribution at LHT and LNT have been investigated while the F‐band is systematically bleached.
Contributions to the kinematical theory of diffraction contrast from screw dislocations
Authors: Coghlan W. A. , Nix W. D.
Published: July 2007

The images of screw dislocations have been evaluated with the kinematical theory of electron diffraction using numerical techniques. The advantage of this method is that the periodic term in the diffracted intensity can be treated. It is found that because of this periodic term a screw dislocation for which n = g · b = 1 will be nearly invisible for certain foil thicknesses, deviations from the Bragg angle, and dislocation positions in the foil. On the basis of these findings, it is proposed that errors in Burgers vector determinations are possible.
Optische und elektrische Messungen an dünnen Thallium(III)‐Oxydschichten
Authors: Geserich H. P.
Published: July 2007

Durch Kathodenzerstäubung wurden dünne polykristalline Tl2O3−Schichten hergestellt. Sie besaßen auf Grund eines stark unterstöchiometrischen Sauerstoffanteils eine hohe Konzentration freier Elektronen (ne ≈︁ 7 × 1020 cm−3). An Schichten mit genügend hoher Elektronenbeweglichkeit (μ = 75 bis 100 cm2/Vs) wurden die optischen Konstanten zwischen 0,2 und 4,5 μm ermittelt. Aus dem Dispersions‐ und Absorptionsverlauf im Ultraroten wurden die effektive Masse im Leitungsband (m* = 0,32 m0) und der Einfluß des Fermi‐Niveaus auf die Absorption durch freie Ladungsträger beim entarteten Halbleiter bestimmt. Aus dem Absorptionsverlauf im sichtbaren und ultravioletten Spektralbereich ergaben sich Bandabstände für direkte (ΔEdirekt = 2,25 eV) und indirekte Übergänge, letztere modifiziert durch den Burstein‐Effekt (ΔEindirekt + ξ ≈︁ 1,4 eV).
A systematic numerical error in APW calculations
Authors: Greisen F. C.
Published: July 2007

A recalculation of the final stage of two self‐consistent APW band structure calculations for Cu and Al shows the stated energies to be in error up to 0.08 Ry. It is also shown that a probable source of the error is an incorrect starting of the radial integrations.
Consistent Treatment of Symmetry in the Tight Binding Approximation
Authors: Egorov R. F. , Reser B. I. , Shirokovskii V. P.
Published: July 2007

The form of Hamiltonian matrix components in the tight binding approximation are deduced group‐theoretically taking into account the space symmetry of the problem, time‐reversal symmetry and hermiticity of the Hamiltonian. This method enables the calculations for any complicated crystal structure, when the spin is included respectively not regarded. Calculations for hexagonal close‐packed structure illustrate the procedure.
Notes on a Valence Electron Model of Atoms
Authors: Kunz A. B.
Published: July 2007

The exact solutions to the “valence‐electron model Hamiltonian” are considered. This model was suggested in recent articles by Wang. It is shown that for a certain range of C in the potential term –C r−2, solutions to the problem exist which are formally identical to the usual solutions for the hydrogen atom problem. It is also seen that for a wide range of the parameter C, there exist no solutions for which the Hamiltonian is Hermitian. The implications of this are discussed, and uses of this model considered.
The Ionic Conductivity of CsCl Doped with K+, Rb+, and Br−
Authors: Arends J. , Nijboer H.
Published: July 2007

Ionic conductivity measurements are made on single crystals of CsCl doped with Rb+, K+, and Br−. The results indicate that small concentrations of these monovalent ions have a marked effect on the activation energies in the NaCl and the CsCl phases and also on the hysteresis behaviour. It is shown that the decrease of the activation energies in crystals doped with Rb+ and K+ and the independence of these energies of the Br− content, can be described in terms of the size of the ions. The decrease of the pre‐exponential factor in crystals doped with K+ or Rb+ is probably due to a change in the frequency spectrum of the lattice vibrations.
A Possibility for Band Structure Determination: Intraband and Donor‐Band Transitions of Crystal Electrons in High Electric Fields
Authors: Döhler G. , Hacker K.
Published: July 2007

The electron states of a crystal in an electric field are Kane functions, the Wannier‐Stark levels are the corresponding energy levels. Electromagnetic transitions between them in the infrared region are considered. From the probability of spontaneous transitions as well as from the hf current produced when the field is changed abruptly the band structure can be determined. The absorption constant for donor‐band transitions shows steps as a function of frequency, the tunneling probability shows steps as a function of the field. Both facts can be used to prove the existence of the Wannier‐Stark levels. The absorption threshold is shifted (Franz‐Keldysh effect). The influence of phonons, imperfections and the electron‐electron interaction is estimated.
Planar Hall Effect in Ferromagnetic Films
Authors: Ky Vu Dinh
Published: July 2007

The planar Hall effect of Ni, Fe, Co and Ni‐Fe films with thicknesses between 100 and 1500 Å is investigated in the temperature range 77 to 293°K. It is shown that the experimental data obtained may be explained by assuming that the mechanism of scattering and reflection on film surfaces does not give an appreciable contribution to the planar Hall effect.
Calculation of the Width of the Second Conduction Band in Anthracene Crystals from Photoemission Data
Authors: Baessler H. , Riehl N. , Vaubel G.
Published: July 2007

The spectral dependence of the photoemission of electrons from a metal into a narrow conduction band of a crystal is calculated qualitatively. It is shown that the Fowler relation jph ∼ (h v–χ)2 holds for χ ≦ h v ≦ χ + δ where χ denotes the energy difference between the Fermi level of the metal and the bottom of the conduction band and δ the band width. For h v ≧ χ + δ the current approaches a saturation value. The model is applied to the description of the photoemission of electrons from a Na and a Ca cathode into the first and the second conduction band of an anthracene crystal. The width of the second band is found to be (0.5 ± 0.1) eV. The energy gap between the top of this band and the next higher (third) conducting state is at least 0.6 eV.
Some Unifying Relations for Moving Dislocations
Authors: Beltz R. J. , Davis T. L. , Malén K.
Published: July 2007

Lothe's formula for the self‐force on a bent dislocation and Brown's formula for the stress in the plane of a planar loop are generalized to be valid for uniformly moving dislocations when the energy factor is replaced by the Lagrangian factor. Application to straight dislocations in isotropic media shows that the screw dislocation becomes unstable with regard to bends at high velocities. The Lagrangian factor is also used to extend Lothe's representation of the energy flow along a moving straight dislocation and to show the relationship between the mass, the back stress in acceleration, and the energy radiation from an oscillating straight dislocation.
On Electron Mirror Microscopic Observations of the Details of p‐n Junction Regions in Si
Authors: Igras E. , Warmińaski T.
Published: July 2007

Electron mirror microscopic observations of lithium p‐n and p‐i‐n junctions in Si show that the contrast of the junction boundary strongly decreases after being irradiated with electrons. Simultaneously the process of saturation with lithium of the micro‐cracks present on the surface in the neighbourhood of the junction line is observed. The observed process is interpreted in terms of the field extraction of lithium ions from the deeper lying positions into the surface. The electric field responsible for the extraction of lithium ions originates from the electrons impinging on a high resistive solid polymer film formed on the crystal in the course of observation. A similar process, though with slower rate, was observed on p‐n junctions obtained by the diffusion of aluminum into n‐type silicon.
Contrast of a Stacking Fault on X‐Ray Topographs
Authors: Authier A.
Published: July 2007

The contrast of the image of a stacking fault on a section topograph is discussed in detail. The intensity distribution of the X‐rays reflected by a crystal containing a stacking fault is the sum of three terms: the first one is due to interferences between waves which have suffered no interbranch scattering, the third term is a cross term due to interferences between waves of both types. The latter is shown to be the predominant term when the crystal is absorbing. This is confirmed by experiment. The derivation has been done using Kato's spherical wave approach and the stationary phase method. The expressions are given for an absorbing crystal and an asymmetrical orientation of the reflecting planes and the stacking fault with respect to the crystal faces. There is good agreement between the calculated intensity distribution and that observed in the image of a stacking fault.
Studies of the Effect of Annealing on Extended Dislocation Nodes in Silver‐Tin Alloys
Authors: Ives L. K. , Ruff A. W.
Published: July 2007

Extended dislocation nodes have been observed by transmission electron microscopy and measured in several solid solution silver‐tin alloys after annealing at elevated temperatures. The intrinsic stacking fault energies were determined and compared with previously reported values for freshly deformed specimens. Only small irreversible changes in the fault energy were found after annealing up to 600°C, in contrast to results found in some other alloy systems. The effect of oxygen on the node extensions in pure silver was also studied.
Motion of Markers and Bubbles in Solids by Self‐Diffusion in a Temperature Gradient
Authors: Biersack J. , Diez W.
Published: July 2007

In a pure substance a temperature gradient gives rise to a current of atoms relative to the lattice planes. This current is compensated by the motion of lattice planes in the end face system. It is shown that markers or bubbles are not fixed to the lattice planes in the case of a free surface boundary condition. Thus such markers do not indicate the motion of lattice planes as was formerly supposed. Another mechanism for the motion of such markers is therefore proposed: the disturbance of the temperature gradient in the vicinity of the marker generates an uncompensated current of atoms, which causes the marker migration. The velocity of elliptical markers can be calculated analytically. The calculation is carried out for spherical bubbles in metals and ionic crystals. Spheres are found to be an equilibrium form of moving bubbles.
Field Effect on Photocarriers in Copper Phthalocyanine Single Crystals
Authors: Devaux P. , Schott M.
Published: July 2007

The photoconductivity of copper phthalocyanine single crystals changes when a high electric field is applied perpendicular to the illuminated surface. The ionization rate of excitons at the surface and the lifetime of the generated carriers change as a result of the variation of the surface charge; lifetime variation alone cannot explain the experimental results. In all the crystals studied the majority carriers for photoconduction are holes at 300°K. The densities of surface acceptors are higher than 1011 cm−2. A different photogeneration mechanism exists for the bulk throughout the investigated range from 3650 to 8150 Å. It dominates, at least under intense excitation, for light being absorbed only weakly.
Untersuchungen zur aktiven Kristallänge im Fließbereich neutronenbestrahlter Kupfereinkristalle. II. Die aktive Kristallänge
Authors: Neuhäuser H.
Published: July 2007

Kinematographische Messungen der aktiven Kristallänge la im Fließbereich neutronenbestrahlter Kupfereinkristalle in Abhängigkeit von Verformungsgeschwindigkeit ( = 2 × 10−6 bis 4 × 10−12mm/s), Temperatur (90 bis 360°K) und Bestrahlungsdosis (5 × 1017 bis 7 × 1018 n/cm2) ergeben Werte für la zwischen 20 und 2000 Å. Bei fester Temperatur und Dosis wächst die aktive Kristallänge mit der Abgleitgeschwindigkeit gemäß la = la 0–la 1/(1 + t0 ) [2]. Von den Parametern la 0, la 1 und t0 nimmt t0 mit zunehmender Temperatur und Dosis ab. Für ⪆ 10−4 mm/s zeigt sich eine deutliche Abweichung von der Proportionalität zwischen Abgleitgeschwindigkeit und Verformungsgeschwindigkeit . Bei fester Dehngeschwindigkeit variiert sowohl mit der Temperatur wie mit der Dosis: la nimmt mit zunehmender Temperatur und zunehmender Dosis ab. Die Abhängigkeiten werden qualitativ diskutiert.
Mössbauer Spectra in the Presence of Electron Spin Relaxation (II)
Authors: Gabriel H. , Bosse J. , Rander K.
Published: July 2007

Basing on the simple model of spin‐lattice relaxation used by Afanasev and Kagan [3], we have investigated the modifications of the Mössbauer line shape due to relaxation effects. Utilizing Zwanzig's formalism as in I, we eliminate the bath (lattice) variables and retain only the Hamiltonian for the entire Mössbauer ion in the final formal expressions for the line shape. The essential difference compared to I is that in the present paper the electronic shell of the respective nucleus is included in the quantum mechanical subsystem. Therefore this theory is applicable to all relaxation rates. This has already been pointed out in [3] and is elucidated here by making evident that all results found by the solution of rate equations or by stochastic model treatments are special cases of the present theory.
Rare‐Gas Diffusion in Neutron‐Irradiated Rubidium Halides
Authors: Felix F. W.
Published: July 2007

The release of radioactive Kr from neutron‐irradiated single crystals of Rb halides is measured at temperatures ranging from 150°C up to the melting point. The release behaviour is similar to earlier results on the K halides [1]. The activation energies for RbCl, RbBr, and RbI at higher temperatures are 0.56, 0.30, and 0.31 eV, respectively. It is assumed that Kr diffuses by an interstitial mechanism. At lower temperatures a stronger dependence is found, which is attributed to the interaction of the gas atoms with defects. The activation energies in this region are 2.04, 1.68, and 1.41 eV, respectively. RbF shows only a single activation energy of 1.38 eV. In RbI the simultaneous diffusion of Kr and Xe is investigated.
Dislocations and Persistent Slip Bands in Copper Single Crystals Fatigued at Low Stress Amplitude
Authors: Lukáš P. , Klesnil M. , Krejčí J.
Published: July 2007

Persistent slip bands in fatigued copper single crystals are studied by means of transmission electron microscopy of surface thin foils, both parallel and nonparallel to the surface. Comparing the observations from the different nonparallel sections a three‐dimensional model of the internal structure may be constructed. Dislocations with all six possible Burgers vectors of the type 1/2 〈0011〉 are found in the structure. This demonstrates the microscopic action of the secondary slip systems during the low stress fatigue. The macroscopic action of the secondary systems, which is connected with the cell structure formation, is typical for the high stress fatigue. Surface extrusions are found to be related to the dislocation structure below the surface.
Diffusion of Mn2+ in AgCl and AgBr Crystals
Authors: Süptitz P. , Weidmann R.
Published: July 2007

The diffusion of Mn2+ in undoped and Mn‐doped AgBr and AgCl crystals is measured in dependence on temperature with the aid of radioactive tracers (Mn54). For AgBr:Mn the concentration dependence of the diffusion coefficient D is determined, there is a qualitative correspondence to the assumption of Mnc □c associates and a migration of the foreign ions via cation vacancies. The enthalpies for association (Ha = 0.22 eV for AgBr and 0.28 eV for AgCl) and for migration (Hm = 0.74 eV for AgBr and 0.56 eV for AgCl) are approximatively determined from the temperature dependence of D.
Interstitial Solute Trapping in Irradiated and Quenched Iron
Authors: Wuttig M. , Stanley J. T. , Birnbaum H. K.
Published: July 2007

The interaction of interstitial carbon and nitrogen solutes with defects produced by low temperature neutron irradiation and by quenching was studied in high purity and Ferrovac E iron. Magnetic disaccommodation techniques were applied to determine the interstitial solute content after irradiation and upon annealing. Doses of about 1017 neutrons/cm2 caused the trapping of about 20 ppm (atomic) interstitial solutes at 65 (carbon) and 40°C (nitrogen). Trapping of carbon in a Ferrovac E iron alloy occurred during a fast quench from 880°C. After trapping, the interstitial solutes reappeared in solid solution at 300 (carbon, neutron irradiation), 200 (nitrogen, neutron irradiation), and 620°C (carbon, quenching). Various possibilities for the defect traps were considered and it was concluded that trapping of the interstitial solutes occurred at iron interstitial clusters after neutron irradiation and at vacancy type defects after quenching.
Pseudopotentials and the Knight Shift
Authors: Holland B. W.
Published: July 2007

An expression for the Knight shift, accurate to zero order in the pseudopotential, is derived and tested by calculations for Li, Na, Al, Ga, and Cs. The calculations take at most a few hours, and can be used to decide rapidly for any metal whether the pseudopotential method is likely to prove fruitful in general for that metal. In particular the results indicate whether in a more accurate calculation of the Knight shift or change in Knight shift with temperature, pressure or alloy composition, the pseudopotential approach would be appropriate, and whether relativistic, orbital or core polarisation effects might be significant.
Elastisches und thermoelastisches Verhalten von MgF2 und MnF2
Authors: Haussühl S.
Published: July 2007

Die elastischen und thermoelastischen Konstanten von MgF2 und MnF2 wurden mit dem verbesserten Schaefer‐Bergmann‐Verfahren gemessen. Die beobachtete Anisotropie und auch der kleine Scherwiderstand (c11 ‐ c12)/2, der die geringe mechanische Festigkeit des Rutiltyps bewirkt, lassen sich qualitativ aus dem Verlauf der Hauptbindungsketten deuten. Die thermoelastischen Eigenschaften, die Abweichung von den Cauchy‐Relationen und auch die Kompressibilität entsprechen dem Verhalten anderer isotyper Kristalle. Aus dem Vergleich der Kompressibilität von Rutil und MgF2 ergibt sich ein Hinweis auf eine Schwächung der polaren Bindung im Rutil zugunsten eines kovalenten Anteils.
Paramagnetic Resonance Spectrum of Gadolinium in CdWO4 Single Crystals
Authors: Kratêna L. , Žďánský K. , Šik V.
Published: July 2007

The paramagnetic resonance spectrum of Gd3+ in CdWO4 is measured at 24 GHz at room temperature. The parameters of the spin Hamiltonian are determined by fitting of the angular dependence of the spectrum. The values of the zero‐field splitting of Gd3+ and Mn2+ in CdWO4 and CaWO4 are compared and an appropriate mechanism for explaining these values is discussed.
The Growth and Electrical Characteristics of Epitaxial Layers of Zinc Selenide on p‐Type Germanium
Authors: Calow J. T. , Owen S. J. T. , Webb P. W.
Published: July 2007

The experimental details are given of an evaporation technique for producing epitaxial layers of zinc selenide on 0.1 Ωcm p‐type germanium substrates. The degree of crystal order in the deposited layer is presented and the results show that, whilst the (100) orientation readily produces epitaxial layers of zinc selenide, the (110) and (111) orientations are more restricted. The preliminary electrical characteristics of the devices formed on the (100) substrate indicate that, at the higher growth temperatures, an interface layer is formed between the germanium and zinc selenide.
Specific Heat of Ice near the “Ferroelectric” Transition Temperature
Authors: van den Beukel A.
Published: July 2007

According to Dengel et al. [1] a transition (believed to be ferroelectric) occurs in ice near 100 °K. Specific heat measurements in this temperature range show the existence of two peaks, at 104 and132 °K, respectively. The excess heat and the transition entropy corresponding to these peaks amount to (4.3 ± 0.8) cal/mol and to about 0.04 cal/mol °K, respectively.
A Curvature in the In D versus 1/T Plot for Self‐Diffusion in Nickel at Temperatures from 980 to 1400°C
Authors: Bakker H.
Published: July 2007

A rather gradual curvature was found for the In D versus 1/T plot for tracer‐self‐diffusion in nickel single crystals at temperatures from 980 to 1400 °C. The activation energies and frequency factors at the highest and lowest temperatures were in agreement with values measured by other investigators in a similar temperature region. It proved to be possible to analyse the curve in terms of contributions of single and multiple vacancies. Especially accurate values of the characteristic quantities for the diffusion via single vacancies were obtained. Other possible explanations of the curvature were investigated, but rejected.
Polaronic Impurity Hopping Conduction
Authors: Schnakenberg J.
Published: July 2007

Impurity hopping conduction in polar lattices and amorphous substances is investigated by application of the canonical transformation of the small polaron theory. In the case of acoustic coupling only, the results of Miller and Abrahams and Gosar for one‐phonon processes are recovered and compared with the contributions of multi‐phonon processes. In the polar case the assisting roles of acoustic and polar phonons are discussed seperately at temperatures T > θ/2 and T <θ/2 (θ being the Debye temperature). The type of the temperature dependence of the conductivity is determined.
On the Problem of Kinematic Interaction in the Quantum Theory of Magnetism
Authors: Lalović D. I. , Tošić B. S. , Žakula R. B.
Published: July 2007

The work considers the problem of the kinematic interaction of elementary excitations in the quantum theory of magnetism. In order to avoid the appearance of so‐called non‐physical states, a generalization of the Holstein‐Primakoff representation is suggested. It is shown that in calculating dynamic characteristics of magnon systems the Holstein‐Primakoff representation can be applied consistently only up to terms of the order 2 S, and not up to terms of the order 2 S +1, as it is tacitly assumed. In addition, a Pauli representation of spin operators for spins S = 1 and S = 3/2 is given.
Displacive Vibronic Phase Transitions in Narrow‐Gap Semiconductors
Authors: Kristoffel N. , Konsin P.
Published: July 2007

Displacive phase transitions are considered in small‐gap semiconductors due to the electron‐phonon interaction of two bands. The Helmholtz free energy of the system is obtained on the basis of the electron spectrum renormalized by the interaction. The temperature dependent low‐symmetry lattice distortion, renormalized frequencies of the active “soft”; optical branch in both phases, the Curie temperature, etc., are obtained. By means of the Green's function method combinative vibronic frequencies of the system are found. The dielectric susceptibility which is essentially determined by active vibrations is calculated and the general picture of similar (ferroelectric) phase transitions is discussed.