Elektronische Wärmeleitung von supraleitenden Blei-Mangan-Legierungen

Measurements of the electronic thermal conductivity of superconducting lead and lead-manganese-alloys are reported. The samples are quench condensed-films. The thermal conductance of lead films is in good agreement with the BRT-theory. In spite of lead-manganese perhaps being a Kondo-system the thermal conductivity of this alloy is reasonably well described by the Ambegaokar-Griffin theory. Our measurements do not agree with those on indium-manganese alloys reported by other authors.     

Das kritische Magnetfeld von dünnen supraleitenden Doppelschichten

Thin superposed films of two superconductors or of a superconductor and a normal metal in a surface parallel magnetic field are considered, assuming that the mean free path of electrons is very short (dirty limit) and that the films are very thin (Cooper limit). From the linearized integral equation for the order parameter and the diffusion equation for the kernel with appropriate boundary conditions at the surfaces and at the interface, an equation for the critical magnetic field is derived. For small magnetic fields and for superposed films consisting of metals which are not too different in their physical properties, our results are in agreement with those obtained earlier byKlein andFischer. For high magnetic fields, however, there are essential differences.     

Zur Theorie der Übergangstemperaturen von supraleitenden Doppelschichten (Proximity-Effekt)

A theory of the transition temperature of superconducting, superposed films is given by generalizing the methods ofde Gennes andWerthamer. It is shown that the transition temperature of nonhomogeneous superconductors obeys a general rule, which is formally of the same kind as the corresponding formula for homogeneous superconductors and is valid for all mean free paths. The results ofWerthamer follow analytically in the dirty limit if the transition temperatures of the superposed films are nearly equal, but there is numerical agreement for almost all superconductor-superconductor films. In the thin film limit and for normalconductor-superconductor films there are essential deviations. The theory is in good accord with the experimental data. By calculating the unknown interaction constant of copper from the experimental transition temperatures of superposed Cu-Pb films one gets for copper a transition temperature of the order of 10^?2°K.     

Die räumliche Magnetfeldverteilung und kritische Stromdichte in supraleitenden Blei-Wismut-Legierungen

Measurements of the spatial distribution of magnetic fields within superconductors were made with alloys of lead-bismuth, which allow for a large variation of superconducting properties. From these measurements critical current densities were derived as function of local magnetic field, and qualitative informations about surface currents are obtained. By Friedel et al. (1963) a field dependence of critial current density has been calculated, which makes a characteristic shape to be expected at low fields. This shape was found experimentally. A semiempirical extension of the relation given byKim et al. (1962) andAnderson (1962) is proposed, which satisfactory describes the measured current densities in the whole field range.     

Das kritische Magnetfeld Hc∥ von dünnen supraleitenden Filmen

Thin superconducting films in a surface parallel magnetic field are considered, assuming that the order parameter is constant in space. Without any further restrictions on the film thickness,a, an equation for the critical field is derived. In the clean limit, this equation is valid only in the vicinity of T_c, but in the dirty limit it is valid for all temperatures. Our results, for specular reflection, are identical with those obtained byThompson andBaratoff. But for not too thin films we find essential differences between the results for specular and for diffus reflection. For very thin films (a?v/2πT _c), considered in detail byde Gennes andTinkham and byShapoval, our results are in agreement with those obtained byShapoval. In the opposit limit (a?v/2π T _c), the most essential corrections to the Ginzburg-Landau result obtained byLüders are rederived.     

Zur Vorsensibilisierung von Manganaktivierten Zinkkadmiumsulfiden durch elektrische Felder und Infrarotstrahlung

The powder phosphor ZnCdS-Mn was used to make a more detailed investigation into memory, which was first described by Destriau in 1958. The effect of a field and infra-red radiation is modified by prior sensitization of the luminophore; this is apparent during further X-ray radiation primarily as a much higher luminescence intensity which later slowly decreases. A comparison of the results of measuring the brightness and charge on an electroluminescence panel permits conclusions to be reached on the actual mechanism. When a field is applied it excites polarization, the field of which does not have a great influence on the effect studied.     

Die Elektrolumineszenz von Einkristallen von ZnO

Zusammenfassung Der Wert der Spannung des Feldes, die quadratische Abhängigkeit des Leuchtens vom Strom, die äu\erst gute übereinstimmung der Abhängigkeiten der Ionisationszahl von der Spannung, welche experimentell wie auch von der Theorie der Multiplikation der Elektronen ausgehend gewonnen wurden, entsprechen somit dem Mechanismus der Sto\ionisation in ZnO. Diese Schlu\folgerung bleibt, wie zusätzliche Nachprüfungen ergeben, auch bei der Aufhebung einiger Vereinfachungen, die bei der Berechnung vorgenommen wurden (z. B. bei der Berücksichtigung schwächerer Abhängigkeiten(t), k(E), der Breite der Sperrzone von der Temperatur usw.) unverändert.Da im Falle der Isolation der Kristalle von den Elektroden die Herkunft der Oberflächensperren dieselbe bleibt, können die Ergebnisse dieser Arbeit auch für die Deutung der Eigenschaften des Destriau-Effektes in ZnO verwertet werden. Sie können anscheinend auch auf das Leuchten homogener Kristalle von ZnS mit ungefähr gleicher elektrischer Leitfähigkeit und der Sperre an der Kathode bezogen werden.

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We observed the same effect on ZnO single crystals as Destriau and Losev. We studied light emission and the electric properties of single crystals with a rectifying contact, which was switched on in the non-transmitting direction. It was found that the dependence of the number of ionizations on each electron, which passes through the contact, on the voltage, which was determined by comparing the experimental results with the diffusion theory of rectification, agrees with the dependence calculated by means of the multiplication theory of electrons in semi-conductors. The conclusion was reached that inelastic collisions play a greater role in ZnO as the excitation mechanism. The calculated voltage dependence of electroluminescence is very close to the measured dependence.

     

Die Herstellung von Aluminiumnitrid

Zur Erzeugung von Kohlenstoff-14 in Kernreaktoren nach der Gleichung N-14 (n, p) C-14 wird auf Grund vieler physikalischer Parameter, wie hohe Temperaturbeständigkeit, holier Stickstoffgehalt (bezogen auf die Masseeinheit) und geringerer Einfangsquerschnitt für Neutronen der metallischen Komponente sowie relativ leichte Abtrennung des gebildeten Kohlenstoffs Aluminiumnitrid eingesetzt. Die Amvendung des Aluminiumnitrids fur die angeführte Kernreaktion erfordert den Einsatz von reinsten Materialien, besonders den Ausschluß von Kohlenstoff und dessen Verbindungen. Aus diesem Grunde ist es nicht möglich, das in der Technik angewandte Verfahren, die Herstellung aus Bauxit, anzuwenden.     

Die Sprungtemperatur von Supraleitern

An iteration procedure allows to find an equation for the critical temperatureT _c of superconductors starting from the linearized Eliashberg equations without using any cutoff parameters or a Coulomb pseudopotential. Explicit calculation ofT _c for a simple model leads to Morel, Anderson and McMillan's^1,2 expression thereby allowing for a physical interpretation of the commonly used approximation for the Coulombpseudopotential.     

Die Optimierung von Trennverfahren

Es wird eine allgemeine Transportformel für Trennverfahren aufgestellt, die das Konzentrationsgefälle als Funktion der Entnahme darstellt und in deren Koeffizienten die individuellen Eigenschaften (Elementartrennfaktor, Umlaufströmung usw.) eines jeden Trennverfahrens zum Ausdruck kommen. Aus den Optimierungsbedingungen folgen eine Anzahl von allgemeinen Gesetzmüβigkeiten, die für alle Trennverfahren Gültigkeit haben. Die Dimensionen aller optimal arbeitenden Trennkaskaden lassen sich mittels eines Normaldiagramms auf graphischem Wege ermitteln.