bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Critical Field in Superconducting Vanadium
Authors: van Gurp G. J.
Published: July 2007

The critical field Hc2 of superconducting vanadium is determined from critical current measurements on cold‐rolled and annealed foils and on a single crystal. The temperature dependence is found to be stronger than predicted by theory. The critical field is found to be anisotropic in the single crystal. Values of χ1 = Hc2/Hc χ2 are determined which, by ecxtrapolation to zero resistivity, show that pure vanadium is a type II superconductor with χ1 comparable to that for pure niobium.
Untersuchungen der Bereichstruktur von Nickeleinkristallen II. Messungen und Beobachtungen an prismatischen Kristallen mit 〈110〉 als Achse
Authors: Schwink Ch. , Grüter O.
Published: July 2007

Unsere Beobachtungen und Messungen an zweizähligen Nickelkristallen erstrecken sich auf den gesamten Feldbereich, in dem periodische Bitterstreifen auftreten Unterschiede zwischen schlanken und gedrungenen Kristallen werden darauf zurückgeführt, daß bei letzteren das Feld über den Probenquerschnitt nicht homogen ist. Das entmagnetisierende Feld der Kristalle nimmt zunächst linear mit der Magnetisierung bis zu einem Maximalwert zu, darüber fällt es aber wieder auf einen Sättigungswert asymptotisch ab. Die Hauptlinien der Bittermuster auf den Seitenflächen der Kristalle trennen stets zwei Bereiche mit konvexem Winkel zwischen den Magnetisierungsrichtungen. Die Kurve der Periodenbreite mit dem Feld zeigt für schlanke Kristalle einen charakteristischen, stufenartigen Verlauf; er läßt sich mit der Entwicklung der Bittermuster auf den Seitenflächen der Kristalle korrelieren. Das Auftreten periodischer Bitterstreifen bis zu Feldern über 115 Oe läßt sich durch Berücksichtigung von K2 verstehen.
Die kritische Schubspannug kubischer Kristalle mit Fehlstellen tetragonaler Symmetrie IV. Die untere Streckgrenze von α‐Eisen
Authors: Frank W.
Published: July 2007

An Hand von Beispielen wird gezeigt, daß bei α‐Eisen üblichen Kohlenstoffgehaltes unterhalb Raumtemperatur die Temperaturabhängigkeit der unteren Streckgrenze τ0 quantitativ durch kurzreichende elastische Wechselwirkungskräfte erklärt werden kann, welche der in der Nähe der Gleitebenen befindliche Kohlenstoff auf die Versetzungen ausübt. Bei mehr als 0,1 At% C liegt der wirksame Anteil in Form kleiner Ausscheidungen, bei niedrigeren C‐Gehalten interstitiell gelöst vor. Bei hohen Gehalten an gelöstem Kohlenstoff trägt dieser außerdem über den induzierten Snoek‐Effekt zu τ0 bei. Bei den bisher untersuchten C‐armen Proben wird τ0 durch den Sauerstoffgehalt bestimmt.
Elektronenmikroskopie kleiner Fehlstellenagglomerate in bestrahlten Metallen II. Untersuchungen an neutronen‐ und ionenbestrahltem Kupfer sowie neutronenbestrahltem Nickel
Authors: Rühle M.
Published: July 2007

Die nach Neutronen‐ und Ionenbestrahlung in Kupfer sowie die nach Neutronenbestrahlung in Nickel im Elektronenmikroskop beobachtbaren Defekte werden untersucht. Durch quantitativen Vergleich der aus der Theorie des Kontrastes folgenden Kontrastbreite mit den beobachteten Defektgrößen läßt sich die wahre Größe und Größenverteilung der Agglomerate ermitteln. Die Analyse des Defekttyps ergab (siehe [1]), daß sowohl nach Neutronen‐ als auch nach Ionenbestrahlung (im Mikroskop mit 100 kV‐ bzw. 40 kV‐Ionen) nahezu alle beobachtbaren Defekte in Kupfer durch Kondensation von Leerstellen entstanden waren. Dasselbe ergab sich auch für die beobachtbaren Defekte in neutronenbestrahltem Nickel. Die bei der Bestrahlung auch gebildeten Zwischengitteratome müssen deshalb entweder an Senken (Korngrenzen, Versetzungen, Einzelleerstellen) ausgeheilt oder zu noch nicht im Elektronenmikroskop auflösbaren Defekten agglomeriert sein. Durch einen quantitativen Vergleich der beobachteten Defektdichte mit dem Verlauf der Energieverteilungskurve der primären Rückstoßatome folgt, daß alle primären Rückstoßatome, deren Energie größer als (30 ± 10) keV ist, einen im Elektronenmikroskop sichtbaren Defekt erzeugen.
Nuclear Magnetic Resonance in Liquid Gallium Alloys
Authors: van Der Lugt W. , van Der Molen S. B.
Published: July 2007

The Knight shifts of the Ga, In, and Sn nuclear magnetic resonance in liquid Ga‐In, Ga‐Sn, and Ga‐Zn alloys are determined as a function of the concentration. The measurements cover the entire range of concentration for the Ga‐In and Ga‐Sn alloys and concentrations up to 40 at% Zn for the Ga‐Zn alloys. The most important result is the insensitivity of the Knight shift to concentration variations in each of the three alloy systems. The results are discussed in terms of two simple models; these models fail to give a qualitative explanation of the experimental data.
A New Approach to the Vibronic Spectra of Molecular Crystals
Authors: Broude V. L. , Rashba E. I. , Sheka E. F.
Published: July 2007

A study is made of the experimental consequences of the theory of the vibrational spectra of molecular crystals presented recently in [3]. A discussion is also given of the model used in this theory. A detailed comparison is made between the theory and experimental results for pure and isotropic doped naphthalene crystals in the M‐band region. The theory accounts for the decay of electronic‐vibrational intra‐molecular excitations into pure electronic and intra‐molecular vibrational excitations by a resonance interaction. In this case the crystal spectrum should exhibit a wide absorption band corresponding to two‐particle excitation. If the reduction of the vibrational frequencies of the molecule accompanying its electronic excitation is comparable with the pure electronic excitation band width, the spectrum should also show a narrow band corresponding to a one‐particle excitation. These bands should be associated with the vibrational band which is observed experimentally. This idea is used to analysis the absorption in the first vibrational transition region of a naphthalene crystal. The one‐ and two‐particle excitation regions are identified and a quantitative analysis of the data is made which is in accordance with the theory. Collective effects, connected with the excitation decay, appear to be important in this transition region. In this connection of particular interest is an analysis of peculiarities of impurity vibrational absorption in isotopic solutions. Comparison between the spectral data naphtalene deutero‐isotopes and the theory also indicates the importance of some complicated collective interactions.
On the Kinetics of the Crystal Phosphor Luminescence
Authors: Antonov‐Romanovskii V. V.
Published: July 2007

On the basis of the diffusion equation for the motion of free charges, a monomolecular recombination probability is calculated for electron‐hole pairs. The calculation includes short‐time luminescence arising from recombination prior to the localization of the electronhole pair and extended luminescence due to recombination after localization. A qualitative discussion is given of the case in which a particular photon creates more than one electronhole pair.
On the Mixed Mechanism of Electron Scattering in InSb Crystals
Authors: Filipchenko A. S. , Nasledov D. N.
Published: July 2007

Experimental data for indium antimonide on the Hall‐mobility of electrons and the thermal e.m.f. in a weak magnetic field are compared with theory taking into account the non‐parabolicity of the conduction band. Formulae are deduced for the thermal e.m.f. and electron mobility for the case of a mixture of electron‐scattering mechanisms. It is then shown from the experimental data that, in doped indium antimonide crystals, mixed scattering does occur which involves impurity ions, and optical and acoustic phonons.
Effect of Different Lattice Defects on the Mobility of Dislocations in Alkali Halide Crystals
Authors: Boyarskaya Yu. S. , Zhitaru R. P. , Koloskova V. G.
Published: July 2007

Single crystals of KCl and NaCl are subjected to additive colouration treatment and X‐irradiation, and their hardening and softening observed. It is found that F‐centres and colloids have no appreciable effect on the mobility of dislocations. The assumption is made that certain defects are responsible for the hardening of irradiated NaCl crystals. These defects are due to soft irradiation and it is possible that they may be concerned with the generation of new vacancies during the irradiation.
Local Mode Absorption by U‐Centres in Alkali‐Halide Mixed Crystals
Authors: Barth W. , Fritz B.
Published: July 2007

The local mode absorption bands of U‐centres are affected by the presence of alkali or halogen foreign ions in the host lattice in the following ways: (a) new bands appear, which are displaced to higher and lower frequencies (b) the entire spectrum undergoes a concentration‐dependent shift and broadening. These effects are studied for U‐centres in KCl:Rb+, KCl:Na+, KCl:Br−, RbCl:K+,KBr:Rb+ and RbBr:K+ with doping concentrations between 10−3 and 10−1. Groups of new lines can be attributed to U‐centres having doping ions in the next three shells of neighbouring ions. The intensities of these lines are slightly greater than expected from the statistical probabilities for such configurations. The splitting observed in a characteristic pair of lines compares favourably with a simple calculation for the case of a U‐centre perturbed by a foreign cation in a nearest neigbour (100) position. The relation between the lattice constant and local mode frequency obtained in mixed crystals may be used to discuss lattice relaxation near U‐centres and “quasiharmonic” temperature‐dependent band shifts.
On the Kinetics of Plastic Deformation of Some Alkali Halide Crystals
Authors: Komnik S. N. , Bengus V. Z. , Lyak E. D.
Published: July 2007

A study is made of the kinetics of plastic deformation in LiF, NaCl, KCl, and KBr crystals. This includes the non‐uniformity of the plastic deformation, the strain rate dependence of this non‐uniformity, the strain rate dependence of the flow stress, and the dislocation structure of the deformed crystals. In the above crystals a regular change of the kinetics is found for a decrease of the elastic anisotropy factor A = 2 C44/(C11 – C12). The correlation of the macroscopic behavior of the crystals with their elastic anisotropy is assumed if other conditions are similar.
On the Field Emission of Minority Carriers in Photoconductors
Authors: Döhler G.
Published: July 2007

Layer‐like field inhomogeneities in homogeneous photoconductors are discussed using the model proposed by Kiess and Stöckmann, referring to the field emission of minority carriers. By neglecting diffusion, the stationary solutions obtained are shown to describe the potential variations measured in CdS by Kiess indicating a new current saturation effect in photoconductors. Some experimental results on current oscillations observed in Se by Polke and Hasler are also discussed.
Recombination in Semiconductors by a Light Hole Auger Transition
Authors: Beattie A. R. , Smith G.
Published: July 2007

The transition rates for an Auger collision process in semiconductors which involves the light hole band is calculated using a quantum mechanical perturbation method. Spherical energy surfaces are assumed although non parabolic energy bands are allowed for. The temperature dependence of the lifetime of excess carriers due to this process is investigated and the results applied to InSb and InAs in the temperature range 200 to 500°K. The shape of the temperature dependence of this theoretical lifetime for InSb agrees well with experiment at room temperature and above, and when estimates of overlap parameters which occur in the theory are made the absolute magnitude of the lifetime also agrees with experiment. The probability per unit time that a light hole created by a photon of energy h v will take part in an impact ionizing transition is also given as a function of h v. It is concluded that the transition rate for this process is at least comparable to that of the more usual Auger transitions involving the heavy hole and conduction bands only.
Verteilungsfunktion und Driftgeschwindigkeit warmer Elektronen in Germanium
Authors: Franz W. , Miosga P.
Published: July 2007

Das in [1] und [2] beschriebene Verfahren, nach welchem die Verteilungsfunktion heißer Elektronen durch iterative Quadraturen bestimmt wurde, wird für den Fall kleiner elektrischer Felder modifiziert. Die Ergebnisse einer Rechnung für Germanium zeigen bei höheren Temperaturen befriedigende Übereinstimmung mit Messungen.
Influence of Ordering on the Properties of Solid Solutions of the System (HgSe)3x‐(In2Se3)1−x
Authors: Gavrilitsa E. I. , Radautsan S. I.
Published: July 2007

Some results are given of an investigation of the transition effect in solid solutions of the system (HgSe)3x‐(In2Se3)1−x. The concentration and thermal ordering of the atomic components and defects in the cation sublattice are found to have an important effect on the electron mobility and lattice thermal conductivity.
Elastische Konstanten des Flußfadengitters in Supraleitern zweiter Art
Authors: Labusch R.
Published: July 2007

Die elastischen Konstanten des Flußfadengitters in Supraleitern zweiter Art werden erneut aus dem Wechselwirkungspotential zwischen den Flußlinien berechnet. Hierbei werden Irrtümer früherer Autoren vermieden. Unter der vernünftigen Annahme von Dreieckssymmetrie lassen sich alle Konstanten durch die Parameter der gemessenen reversiblen Magnetisierungskurve ausdrücken. Als Beispiel werden die berechneten elastischen Konstanten des Flußfadengitters in Niob bei 4,15°K als Funktion des angelegten Magnetfeldes aufgetragen.
Streuung langsamer Neutronen an polykristallinem Selen und Tellur
Authors: Axmann A. , Gissler W.
Published: July 2007

Mit Hilfe eines Drehkristall‐Flugzeitspektrometers wurde die inelastische Streuung langsamer Neutronen an polykristallinem Selen und Tellur untersucht. Es wurden verschiedene Bandenschwerpunkte gefunden, die in ihrer Lage gut mit den durch Infrarotmessungen [1] ermittelten übereinstimmen, jedoch ist ihre Anzahl kleiner. Dieser Umstand zeigt, daß die neutronenspektroskopisch nicht beobachteten Übergänge von Kombinationen herrühren. Bezüglich des Tellurspektrums ergibt sich eine gute Übereinstimmung mit der Theorie von Hulin [4]. Die Neutronenspektren der beiden isomorphen Kristalle sind einander ähnlich.
Zur Theorie der Erzeugung der zweiten Harmonischen an der Oberfläche eines unmagnetischen, quadratischen, optisch einachsigen Kristalls
Authors: Fischer R.
Published: July 2007

Fällt eine intensive monochromatische, elektromagnetische Welle auf die Grenzfläche eines optisch nichtlinearen Kristalls, so erfolgt eine Wechselwirkung, die zur Erzeugung einer zweiten Harmonischen führen kann. Neben der sich im nichtlinearen Medium ausbreitenden zweiten Harmonischen tritt auch eine reflektierte Harmonische auf. Es werden Verallgemeinerungen des Reflexions‐ und Brechungsgesetzes und der Fresnelschen Formeln für den Fall abgeleitet, daß eine ebene Grundwelle aus einem unmagnetischen, nichtabsorbierenden, isotropen, linearen Medium auf die ebene Grenzfläche eines unmagnetischen, optisch einachsigen, optisch nichtlinearen (quadratischen) Kristalls fällt. Das Problem wird in parametrischer Näherung gelöst. Es wird vorausgesetzt, daß sich die Polarisationswellen nicht in einer Synchronisationsrichtung ausbreiten.
Oscillations collectives de spins et ordre à courte distance
Authors: Villain J.
Published: July 2007

Nous étudions les oscillations collectives de spins à partir des deux premières dérivées non nulles de la fonction de corrélation (Sk(t), S−k) pour t = 0, pour le calcul desquelles nous développons une approximation appropriée. Aux températures inférieures au point de transition on trouve pour la fréquence une formule identique à celle obtenue dans l'approximation des ondes de spin, mais l'approximation est en défaut pour k petit. Il semble que, dans les réseaux tridimensionnels isotropes, les oscillations de spins aient complètement disparu au point de transition. Par contre elles peuvent exister en l'absence d'ordre à grande distance si l'ordre à courte distance est intense, notamment dans un réseau plan ou linéaire.
The Condition for Negative Absorption in Semiconductors
Authors: Landsberg P. T.
Published: July 2007

For a given photon energy h v the condition that the stimulated emission rate exceeds the absorption rate is Fc ‐ Fv > h v when the F's are quasi‐Fermi levels for conduction and valence bands. This holds also if phonons are involved. The condition is generalised here to the case where several electrons and phonons are involved and localised or band states play a part. The condition becomes: The drop in the quasi‐Gibbs free energy of the electron system as a result of one radiative transition must exceed h v.
Interference Effects in Spin Lattice Relaxation by Two‐Phonon Processes
Authors: Stoneham A. M.
Published: July 2007

The usual theory of relaxation by two‐phonon processes assumes that the relaxation rate is the sum of a non‐resonant Raman contribution and resonant Orbach contributions. This neglects terms which may be regarded as interference between these contributions and which appear when several excited states contribute to the relaxation. These terms affect the temperature dependence of the relaxation rate and will affect the values of energy level splittings obtained from the Orbach terms. Further the contributions of the several excited states to the relaxation rate may themselves tend to cancel. The usual approximation of omitting phonon energies in energy denominators is then invalid, as the cancellation is sensitive to their presence. A comparison of the exact theory and the usual theory is made for MgO:Co2+. Agreement with experiment is rather better in the exact treatment, but poor in both cases. Possible reasons for the discrepancy are suggested.
The Yield Point of α‐Copper–Tin Alloys
Authors: Vöhringer O. , Macherauch E.
Published: July 2007

Dynamics tensile tests (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} = 1.6 × 10−4 s−1) are performed on polycrystalline α‐Cu‐Sn alloys. The effects of temperature (T) and composition (c) on the yield point σSt are investigated. In the temperature range T ⪅ 300°K the relation σSt = (a1 ‐ b1 T1/3) \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt c $\end{document} holds where a1 and b1 are constants. This dependence can be estimated theoretically from the elastic interaction of Sn‐atoms with dislocations. Theory and experiment agree quite well.
Orientation Dependence of the Ferroelectricity of T.G.S.
Authors: Jiménez B. , Mendiola J. , Maurer E.
Published: July 2007

The ferroelectric behaviour of T.G.S. single crystals is studied for slabs cut along directions which form gradual orientations with the polar axis [010]. Distinct ferroelectric phenomena are observed for several directions, even for orientations well away from the polar axis, where perfectly defined ferroelectric properties are obtained (hysteresis loop, λ‐curve of the dielectric constant, and maximum switching current). The results are interpreted on the basis of a simple consideration of H‐bond contributions to the ferroelectricity. The theoretical conclusions are in good agreement with the experimental results.
Leitfähigkeit und Feldeffekt reiner Siliziumspaltflächen
Authors: Henzler M.
Published: July 2007

An Siliziumkristallen (etwa 104 ωcm, p‐leitend), die im Ultrahochvakuum gespalten worden waren, wurden Oberflächenleitfähigkeit und Feldeffekt gemessen. Durch eine Abschirmung der Proben und Messung des Feldeffektes für verschiedene Abstände der Feldelektrode konnte der verfälschende Beitrag der oxidbedeckten Seitenflächen ausgeschaltet werden. Die reine Oberfläche ergibt sich als schwach p‐leitend (Δσ = (4,2 ± 1,3) × 10−7 A/V) mit einer hohen Dichte von Oberflächenzuständen (SE = 1014 eV−1 cm−2). Durch Wasserdampf wird die Spaltfläche stark n‐leitend, während durch Sauerstoff die Oberflächenleitfähigkeit nahezu den Minimalwert zwischen p‐ und n‐Leitung annimmt.
Electron Charge Distribution about Zinc Ions in Aluminum
Authors: van Torne L. I.
Published: July 2007

The electron charge density distribution about a zinc solute ion in a dilute aluminum alloy is computed by three different methods. These are: a) an exact method where the solute ion potential is derived from the model potential difference between zinc and aluminum, b) a semiempirical method where the partial wave phase shifts are obtained from alloy specific electrical resistivity, and c) an approximate method where the solute ion potential is represented by a screened Coulomb potential. All three methods are in agreement with the experimentally observed solute ion clustering. Methods a and b also are in agreement with the observed decrease in lattice parameter with increase in zinc content.
Plastische Verformung von Eisen‐II‐Oxid
Authors: Reppich B.
Published: July 2007

Einkristallines und polykristallines Eisen‐II‐Oxid, Fei1–xO, mit einem Kationenleerstellengehalt von 0, 05 ≦ x ≦ 0, 11 wurde im Stauchversuch bei Temperaturen 650 °C ≦ T ≦ 1300 °C statisch und dynamisch verformt. Stationäres Kriechen und dynamisches Fließen lassen sich beschreiben durch die Zustandsgleichung ε˙ = C (1 + bx) σm exp( –U/kT) mit m = 4 und U = (3.54 ± 0,21) eV ⌆ (81, 5 ± 4.8) kcal/mol. Einkristalle sind weicher und duktiler als Polykristalle. Fe1–xO wird mit steigendem Leerstellengehalt x plastischer. Für die beobachtete Streckgrenze werden die von Fe3O4‐Ausscheidungen herrührenden Versetzungsringe verantwortlich gemacht. Die Ergebnisse lassen sich durch ein von der Spannung unterstütztes Klettern von Stufenversetzungen deuten.
Diffusion of Xenon in Barium Fluoride
Authors: Schmeling P.
Published: July 2007

The diffusion of xenon in barium fluoride after irradiation with reactor neutrons is studied. Above 1000 °C the diffusion process is characterized by an activation energy of 3.7 eV and is independent of the neutron dose.
On the Theory of Thermally Activated Processes
Authors: Geszti T.
Published: July 2007

The range of validity of “rate theory” is investigated and a clear distinction is made between “directional” and complete thermalization. It is suggested that the first process determines the hopping character of the motion, while the second determines whether the usual quasi‐equilibrium description is applicable. Macroscopic diffusion is shown always to obey “rate theory”, while frequency‐dependent dielectric or anelastic loss may shown non‐equilibrium effects. In the case in which complete thermalization is slow (although directional thermalization may be fast) a succession of Lorentzian peaks is obtained instead of the single peak predicted by rate theory. Qualitative dynamic conditions are presented for slow thermalization behaviour.
The Determination of the Orientation of Micro‐Crystals Using a Back‐Reflection Kossel Technique and an Electron Probe Microanalyser
Authors: Bevis M. , Swindells N.
Published: July 2007

The determination of the orientation of small single crystals from back‐reflection Kossel patterns obtained by using an electron probe microanalyser is considered. A procedure for determining the indices of directions in the crystal represented by the intersection of Kossel lines is presented, and the way in which this information may be used for determining the orientation of crystals without the aid of the stereographic projection is described. Complementary procedures for determining the full orientation of small crystals and the orientation of interface planes in these crystals are also described. To illustrate these procedures the orientation relationship between annealing twins and the matrix in an f.c.c. crystal has been determined together with the orientation of the twin matrix interface planes.
Surface and Volume Diffusion in Thin Films of the System AgSe
Authors: Pines B. Ya. , Grebennik I. P. , Bazyura R. I. , Zozulya G. V.
Published: July 2007

The course of volume and surface diffusion in thin (10−5 to 10−6 cm) films of the system AgSe was investigated by means of electron diffraction and microscopic studies. The surface diffusion determines the growing speed of the two component region in specimens that have partly superimposed layers of components. Volume diffusion equalizes the concentration in the thickness direction of the film. The kinetics of the surface diffusion of Ag over Se could be stated by observing the displacement of the crystallisation front of amorphous selenium. The surface diffusion of Se over Ag was controlled by the appearing α‐Ag2Se diffraction lines near the edge of the two component region.
ESR Studies of Cu2+ in NH4Cl Single Crystals between 4.2 and 453 °K. I. Spin‐Hamiltonian Parameters and Lattice Constant for NH4Cl
Authors: Pilbrow J. R. , Spaeth J. M.
Published: July 2007

ESR spectra from two different Cu2+ with [100] tetragonal symmetry were observed in NH4Cl single crystals. The spin‐Hamiltonian parameters for both centres were determined in the temperature range 4.2 to 453 °K where NH4Cl has the CsCl structure. The g‐values and hyperfine constants for both centres show a marked anomaly in the vicinity of the λ‐point and significant variations over the whole temperature range. Both centres have essentially a |3 z2 – r2〉 ground state, but with evidence of vibrational admixtures of the |x2 – y2〉 state. In view of possible future calculations of the Cu2+ spin polarization and radial wave function for the ground state, the lattice parameter of NH4Cl and NH4Cl:Cu was measured in the temperature range 105 to 453 °K.
ESR Studies of Cu2+ in NH4Cl Single Crystals between 4.2 and 453 °K. II. Theoretical Analysis: Vibrational Admixtures, Spin Polarization, and 〈r−3〉 for Cu2+ Ions
Authors: Pilbrow J. R. , Spaeth J. M.
Published: July 2007

The temperature dependence of the spin‐Hamiltonian parameters for two Cu2+ centres in NH4Cl single crystals, which were reported in the previous paper (I), is analysed in detail. The results show that, apart from zero point vibrations, higher lattice modes also contribute to the admixture of the |x2 – y2〉 state into the |3 z2 – r2〉 ground state for these centres. For one of the centres there is also evidence that vibrations and reorientations of a single nearest neighbour NH4+ ion contribute to the admixture. From the analysis, the temperature dependence of 〈r−3〉3z2 – r2, a crystal field splitting parameter and the contact contribution to the hyperfine field at the Cu2+ nucleus is obtained. All these quantities vary strongly with temperature and show sudden changes at the λ‐point ( −30.5 °C) for NH4Cl. The temperature dependence of the contact term in the hyperfine interaction can be qualitatively understood in terms of core spin polarization by taking into account the observed changes in the radial distribution of the 3d ground state. The analysis gives further support for the models proposed for the two Cu2+ centres.
On the Theory of Electrical Resistivity of Polyvalent Metals
Authors: Bross H. , Bohn G.
Published: July 2007

In the case of polyvalent metals, the singularities in the transition probability determined by Bardeen can be avoided by performing the integration over the atomic polyhedron instead of the Wigner‐Seitz‐sphere. This new expression for the transition probability is used to compute the temperature‐dependence of the electrical resistivity for aluminium. Anisotropic effects due to the lattice waves are taken into account by a variational procedure. The agreement with experimental results is satisfactory.
Lattice Specific Heats of Thallium and Yttrium
Authors: Gupta R. P.
Published: July 2007

The lattice specific heats of thallium and yttrium are calculated using the electron gas model of Gupta and Dayal for hexagonal metals. The interactions are restricted to fourth neighbours. The force constants are determined from experimental values of the elastic constants. The θ‐T curves calculated from the computed specific heats show a fairly satisfactory agreement with the experimental values, i.e. the difference is not greater than 3% for thallium and 6% for yttrium.
The Influence of Collisions on the Franz‐Keldysh Effect
Authors: Enderlein R.
Published: July 2007

A study is made of the effect fo electron‐phonon and electron‐impurity scattering on the field‐induced change in the optical interband absorption for photon energies near the direct band gap ℏ ω0. It is found that in the presence of collisions the exponential tail of the absorption coefficient at ω < ω0 oscillates and that the oscillations at ω > ω0 are damped. This damping seems to be in quantitative agreement with the experimental results of Hamakawa, Germano and Handler [4].
Role of Carrier Polarization in the Mechanism of the Electroluminescence of ZnSMn Films
Authors: Vlasenko N. A. , Zynio S. A.
Published: July 2007

A polarization which remains constant over a period of time and is caused by the accumulation of carriers in deep surface traps is observed in EL ZnSMn films. The polarization characteristics (i.e., the number of polarization charges, the time‐dependence of its formation and destruction, the ionization energy of the traps, etc.) are determined in order to study the role of carrier polarization in the mechanism of EL. It is established that the polarization mainly affects the change in the internal field and therefore the impact ionization probability. Also, at the instant of voltage‐polarity reversal, the polarization charge ionization leads to an increase in the number of carriers which can accelerate. All the EL properties and features of ZnSMn films may be explained on the basis of an impactionization mechanism if the polarization effects are taken into account.
Electron Spin Resonance of Tl++ Centres in KCl Crystals
Authors: Dreybrodt W. , Silber D.
Published: July 2007

Thallium‐doped KCl crystals are X‐rayed at 77 °K. They are warmed up to 300 °K and then cooled down again to 77 °K. ESR signals showing a resolved hyperfine structure due to six chlorines are observed. These arise from a Tl++ ion on a cation lattice site. The constants of the spin‐Hamiltonian are determined. Using Watanabe's theory [1] the coefficients of the ground state LCAO function are determined from the h.f.s. constants. From these data and from data of the optical absorption spectrum of Tl++ [3] the g‐shift is calculated and compared with the experimental value.
A Model for the Lattice Dynamics of Naphthalene and Anthracene
Authors: Pawley G. S.
Published: July 2007

The lattice dynamics of a model for naphthalene and anthracene is presented. Intermolecular forces of the ‘6‐exp’ interatomic type are assumed, and dispersion curves are calculated. It is stressed that the Raman modes do not involve rotations about the principal inertia axes. Frequency distributions, Debye temperatures and Debye‐Waller factors are calculated, and the validity of using the last to estimate Raman frequencies is assessed. The agreement with experiment is good, except perhaps, for the elastic constants. Finally the thermal diffuse X‐ray scattering is calculated and compared with experiment. The low resolution results agree both with experiment and with the ‘difference Fourier transform’ theory. The high resolution calculation, however, explains the discrepancies between experiment and the earlier theory.
Effect of Concentration on Light Absorption and Dispersion by Impurity Centres in the Case of Weak Electron–Phonon Coupling (II)
Authors: Lubchenko A. F. , Dudkin S. I.
Published: July 2007

The two‐particle Green's function method is used to investigate the dependence of light absorption and dispersion due to substitutional impurity centres upon their concentration in the case of weak electron‐phonon coupling, taking into account the change of the quasi‐elastic constants due to the substitution. At low impurity concentrations the half‐width of the zero‐phonon line and the corresponding dispersion curve as well as their position in the spectrum are shown to vary linearly with concentration; at higher concentration the absorption coefficient may deviate from linearity.
Magnetic Ordering in Uranium Compounds with Crystal Structures of Anti‐Cu2Sb and PbFCl Types. Molecular Field Approximation
Authors: Przystawa J. , Suski W.
Published: July 2007

The eight possible types of collinear magnetic structure are determined in the molecular field approximation with the help of Smart's and Bertaut's methods. The Heisenberg isotropic model with five nearest‐neighbour exchange integrals is used. The stability conditions are presented in terms of phase diagrams.
Tilt Boundaries in Deformed Anthracene Single Crystals
Authors: Robinson P. M. , Scott H. G.
Published: July 2007

Anthracene single crystals have been deformed by cleaving and by bending. In both cases, immobile tilt boundaries approximately perpendicular to the basal planes were observed. These boundaries were slightly asymmetric with respect to the basal planes on either side. It is believed that the boundaries consist mainly of mobile dislocations with Burgers vectors in the basal plane. The asymmetry of the boundaries is thought to be due to the incorporation of a few dislocations whose Burgers vectors lie in the other planes; these dislocations also serve to pin the boundary.
On the Electric and Thermoelectric Properties of Copper Phthalocyanine Single Crystals
Authors: Hamann C.
Published: July 2007

Comparative measurements are made on single crystals of copper phthalocyanine in order to investigate the electric, thermoelectric, and galvanomagnetic properties. A simple model is used to explain the thermoelectric measurements and the space‐charge limited current characteristics. This involves presence of electron traps of concentration of the order of 1013 to 1014 cm−3 and trap depth 0.88 eV below the conduction band. Copper phthalocyanine is an intrinsic semiconductor having an activation energy of 2.0 eV.
Effect of Pressure on the Diffusion of Fe in Ti and Ti + 10% Fe
Authors: Peart R. F.
Published: July 2007

Measurements have been made of the variation of the diffusion coefficient of Fe as a function of hydrostatic pressure in Ti at 902 °C and of Fe in Ti + 10% Fe at 808 °C. Hydrostatic pressures up to 4000 atm were used. For Ti + 10% Fe the diffusion coefficient decreases with pressure and corresponds to a value of 0.6 for the ratio of the activation volume to the atomic volume. For Ti the diffusion coefficient increases nonlinearly with pressure. These results are discussed in terms of diffusion due to vacancies, interstitials, and sub‐grain boundary networks.
The Self‐Energy of Dislocation Configurations Made up of Straight Segments
Authors: de Wit R.
Published: July 2007

Three general expressions are presented: the first is the interaction energy between two non‐parallel straight dislocation segments, the second is the interaction energy between two parallel straight segments, and the third is the self‐energy of a straight segment. These can be used to determine the total energy of any dislocation configuration made up of piecewise straight segments. They differ from previous expressions in the literature primarily in that they are given completely in vector notation and in that the self‐energy includes a core traction term. The expressions are limited to the case of a linear, isotropic, infinite continuum. As an example, the formulas are applied to the case of a stacking‐fault tetrahedron.
Te and Se Centres in AgBr. II. Electronic Structure
Authors: Höhne M. , Stasiw M.
Published: July 2007

The electronic structure of the paramagnetic centre described in Part I is discussed. This centre turns out to be a Se3− – or Te3− – pseudomolecule with 110‐direction. The g‐values and the hyperfine constants of Se3− – but not of Te3− – can be described by assuming the spin‐orbit‐coupling to be small compared with crystal field splitting and neglecting overlap of the atomic wave functions. The ground state wave functions of Te3− are calculated without restriction to small spin‐orbit‐coupling. This method turns out to be not sufficient in the case in question, because overlap plays an important role.
F‐Centres in Alkaline Earth Fluorides
Authors: Feltham P.
Published: July 2007

The ls‐2p transition energy of electrons trapped at fluorine ion vacancies in BaF2 is calculated by means of a continuum approximation, allowing for polarisation. The lattice potential is determined from that previously [8] derived in the evaluation of the F‐centre absorption frequency in CaF2, taking into account lattice isomorphism and differences in the core structures of the respective cations. The calculated value of the energy agrees well with that obtained in additively coloured BaF2 crystals [1] by ESR.
Radio‐Frequency Size Effects in Cadmium in Magnetic Fields Inclined to the Sample Surface
Authors: Naberezhnykh V. P. , Maryakhin A. A.
Published: July 2007

The r.f. size effect is investigated in cadmium, for different field slopes relative to the surface, using a frequency of 5 MHz and magnetic fields up to 104 Oe. When the angle between H and the basic plane of the “lens‐shaped” Fermi surface of the third band is less than 32°, some sections are found with the extremal value of \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{\partial S}}{{\partial K_H }}} \right) $\end{document}, giving the size effect along spiral paths. For H ⊥ [0001] these sections involve KH = 0.41 Å−1 with \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{\partial S}}{{\partial K_H }}} \right)_{ext} $\end{document} = (1.112 ± 0.03) Å−. By changing the field slope angles from zero to 90°, and rotating H in the basic plane, it is possible to observe the change in character of the impedance oscillations on the spiral paths. For slope angles between 7° and 17° the size effect lines at the spherical support point of the „lens”︁ are also observed. This gives the radius of curvature as (1.32 ± 0.1) Å−1.
External Photoeffect from Sensitizing Dyes Adsorbed on Semiconductors
Authors: Akimov I. A. , Bentsa V. M. , Vilesov F. I. , Terenin A. N.
Published: July 2007

A study is made of the spectral distributions of the internal and external photoeffect for ZnO, AgBr, and TlJ before and after dyeing by sensitizers. The results obtained indicate that the excited dye level is situated below the bottom of the conduction band of the n‐type semiconductors (ZnO, AgBr), and that the top of the valence band of the p‐type semiconductor (TlJ) is situated below the ground level of the dye sensitizer. Hence, the spectral sensitization does not occur by charge transfer, but by energy transfer.
Étude de la variation de longueur du plutonium α par autoirradiation à 4 °K
Authors: Lallement R. , Wigley D. A.
Published: July 2007

Nous avons mesuré l'allongement du plutonium α maintenu dans l'hélium liquide. La longueur du plutonium augmente en suivant une loi de la forme ΔL/L = A [1 − exp(−α t)] avec α = 2,2 × 10−4/h et A = 2 × 10−2. La comparaison avec les résultats relatifs à la résistivité montre que la longueur se sature bien moins vite que la résistivité. Cette différence permet de comprendre qualitativement l'existence d'un maximum dans la variation de résistivité avec le temps. La comparaison des deux résultats montre aussi que la saturation de la résistivité n'est pas liée à la saturation de la production des défauts. Des recuits isochrones ont montré l'existence de deux stades de recuits pour les défauts d'autoirradiation, l'un vers 80 °K, l'autre vers 160 °K.
The Influence of Annealing on the Structure of Polycrystalline Permalloy Thin Films
Authors: Puchalska I. B. , Sukiennicki A. , Petykiewicz Z. , Tymosz T.
Published: July 2007

A study is made of the effect of annealing on the structure of permalloy polycrystalline thin films. Thin films of 85% Ni‐15% Fe are investigated using an electron microscope at high temperatures. The results show that annealing causes the growth of irregularities in the thin film surface. In extreme cases this may invalidate the concept of a uniform thin film thickness. The growth of crystallites is not isotropic but occurs most vigorously in the surface of the thin film.
The Influence of the Magnetic Field on the Domain Structure of Ferrimagnetic Oxides with High Anisotropy Field
Authors: Rosenberg M. , Tanasoiu C. , Florescu V.
Published: July 2007

The magnetization process of SrO × (6 − x) Fe2O3 × x Al2O3 single crystals (with 0 ≦ × ≦ 2) is investigated by recording the modifications of the domain structure under the influence of an external magnetic field. It is found that this process occurs in two stages: in the first stage, at lower fields, the magnetization occurs mainly by Bloch wall displacements; in the second stage (at higher fields) regions of the inverse magnetized domains, or entire domains of this type suddenly collapse. For samples with x = 0 and 1 honeycomb domain structures can be obtained by applying a magnetic field along the hard direction.
The Effect of Systematic Reflections on the (110) Extinction Distance in Molybdenum
Authors: Sheinin S. S.
Published: July 2007

The dependence of the (110) extinction distance in molybdenum on Δθ, the deviation from the exact Bragg condition, has been investigated. The results indicate that near the exact Bragg condition (0° < Δθ < 0.5°) the two‐beam theory is in good agreement with experiment. For larger values of Δθ the effects of systematic reflections become important. The agreement between the multi‐beam theory and experiment is excellent for values of Δθ greater than 1.25°. However, for intermediate values of Δθ where the depth periodicities are complex, neither the two‐ or multi‐beam theories give an adequate description of the experimental results obtained.
Untersuchung der anisotropen Abbremsung von niederenergetischen Magnesiumatomen in einem NaCl‐Einkristall bei verschiedenen Temperaturen
Authors: Dutta B. C. , Holtmeyer G. , Kalus J.
Published: July 2007

Es wurde die Kernresonanzfluoreszenz‐(KRF‐)Ausbeute am 1,37 MeV‐Niveau von Mg24, das durch Neutronenbestrahlung von Na23 in einem NaCl‐Einkristall erzeugt wurde, in Abhängigkeit von der Kristallorientierung und Temperatur gemessen. Abhängig von der Temperatur war die KRF‐Ausbeute bei Emission der γ‐Quanten in <110>‐Richtung bis zu 18% größer als bei Emission in < 100 >‐Richtung. Die Ursache der Temperaturabhängigkeit ist eindeutig auf Diffusionsprozesse zurückzuführen. Aus Rechnungen, die mit einem Hartkugelmodell durchgeführt wurden, ergibt sich, daß bei Zimmertemperatur die Gleichgewichtslage des Mg‐Atoms ein raumzentrierter Zwischengitterplatz ist.
Calculations of Dispersion Curves and Specific Heat for LiF and NaCl Using the Breathing Shell Model
Authors: Nüsslein V. , Schröder U.
Published: July 2007

The model for the lattice dynamics of alkali halides as given in a previous paper is generalized to include the case in which both ions are polarizable. Dispersion curves and density of states are calculated for LiF and NaCl at 0 °K. The Debye characteristic temperatures ΘD(T) for 0 °K and 300 °K are computed for these crystals, and good agreement with experimental values is obtained.
Electric Conductivity and Dielectric Absorption Phenomena in Lead Zirconate Ceramics
Authors: Handerek J.
Published: July 2007

Changes in the electrical conductivity of PbZrO3 in the temperature range 200 to 270 °C are investigated using gold, silver and platinum electrodes. Within this temperature range it is found that a spontaneous current exists in the sample showing changes with temperature analogous to the changes governing the electric conductivity. Study of absorption currents when the polarization field is switched off, reveals current hysteresis loops reminescent of electrical hysteresis loops in ferroelectric materials. Hence, the results obtained indicate the presence of a ferroelectric phase in PbZrO3 as well as an electronic mechanism of conductivity.
Determination of Spin Directions and Electric Field Gradient Axes in Vivianite by Polarized Recoil‐Free γ‐Rays
Authors: Gonser U. , Grant R. W.
Published: July 2007

Non‐polarized and linearly polarized recoil‐free γ‐rays (Mössbauer effect) have been used to determine spin directions and the orientation of the electric field gradient (EFG) principal axes for the two iron sites in vivianite. The values obtained for the internal fields, quadrupole splittings, isomer shifts, and the relative orientations of the internal fields and EFG principal axes with respect to the crystal axes are tabulated.
Localized States in Disordered Lattices
Authors: Mott N. F. , Allgaier R. S.
Published: July 2007

This paper investigates the conditions under which localized states occur in three dimensional disordered systems, and considers the relevance of a large body of experimental data on liquids which exhibit non‐metallic behaviour in their conductivities. It is suggested that in many liquids a “pseudogap” a deep minimum in the density of states will occur. It is argued that localized states will appear in this pseudogap when the density of states drops to roughly half its free electron value and that the mean free path is then approximately equal to the wavelength of the electron. It then follows that “hopping” conductivity increasing with increasing temperature will appear when the magnitude of the conductivity falls below a certain value, computed to be in the neighbourhood of 300 Ω−1cm−1. An examination of the known data on about 90 liquids near their melting point suggests that this is in fact the case.
Herring‐Nabarro Creep Studies on the Self‐Diffusion of Iron in the Presence of Solutes
Authors: Hondros E. D.
Published: July 2007

Creep studies have been conducted on pure iron and iron alloys at high temperatures and in the stress range where the Herring‐Nabarro diffusion creep mechanism pertains. Results are presented which show that the diffusion coefficient of pure iron in the δ‐phase agrees within experimental error with the radio‐tracer value and that nitrogen and phosphorus in dilute solid solution enhance the self‐diffusivity of pure iron. The self‐diffusion of iron in the presence of 3.5% Si is expressed by

.
Etude théorique et expérimentale du contraste des images de dislocations
Authors: Balibar F. , Authier A.
Published: July 2007

On compare la distribution d'intensité observée pour une image de dislocation par topographie aux rayons X à celle calculée à l'aide de la théorie de Takagi, pour la même dislocation. Les résultats sont en bon accord. En particulier, on retrouve bien par le calcul les différentes régions de l'image de dislocation avec leurs contrastes respectifs (“image directe”, “image dynamique”, “images intermédiaires”).
Ion‐Bombardment Enhanced Solubility in Solids
Authors: Jech Č.
Published: July 2007

Two labelling techniques are developed which are based on injection of small concentrations of radioactive atoms with a known concentration profile. These techniques are used for studying enhancement of solubility in mica, Al2O3, and NiO induced in these substances by bombardment with Kr ions with energies in the keV region. Mica is found to be the most sensitive, an enhanced solubility of the surface layer being detected for doses as low as 5 × 1012 ions/cm2. The depth of the soluble layer is found to be comparable with the range of the ions. The effects of ion bombardment on solubility seem to arise from lattice damage resulting from the bombardment rather than from the presence of the injected gas.
Energy Distribution of Photoelectrons Created by Al Kα X‐Rays in Alkali Halide Targets
Authors: Karras M. , Suoninen E.
Published: July 2007

The spectra of photoelectrons created by AlKα X‐rays are investigated in CsJ, CsF, LiJ, and LiF photocathodes. The energy distributions of the photoelectrons are determined by measuring the photoelectric current between two concentric spherical electrodes with a variable retarding potential between them. For a LiF target, the electron spectrum is analysed quantitatively using an analytical model for the energy distribution of the K photo and K → LL Auger electrons from fluorine atoms. A strong deviation from Whiddington's law is found for the penetration model of the electrons.