Effect of annealing on the superconducting properties of a-Nb(x)Si(1-x) thin films

a-Nb(x)Si(1-x) thin films with thicknesses down to 25 {\AA} have been structurally characterized by TEM (Transmission Electron Microscopy) measurements. As-deposited or annealed films are shown to be continuous and homogeneous in composition and thickness, up to an annealing temperature of 500{\deg}C. We have carried out low temperature transport measurements on these films close to the superconductor-to-insulator transition (SIT), and shown a qualitative difference between the effect of annealing or composition, and a reduction of the film thickness on the superconducting properties of a-NbSi. These results question the pertinence of the sheet resistance R_square as the relevant parameter to describe the SIT.Comment: 9 pages, 12 figure

Point defect distribution in high-mobility conductive SrTiO3 crystals

We have carried out positron annihilation spectroscopy to characterize the spatial distribution and the nature of vacancy defects in insulating as-received as well as in reduced SrTiO3 substrates exhibiting high-mobility conduction. The substrates were reduced either by ion etching the substrate surfaces or by doping with vacancies during thin film deposition at low pressure and high temperature. We show that Ti-vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects are the same both in ion-etched and substrates reduced during the film growth, and they consist of non-homogeneous distributions of cation-oxygen vacancy complexes. Their spatial extension is tuned from a few microns in ion-etched samples to the whole substrate in specimens reduced during film deposition. Our results shed light on the transport mechanisms of conductive SrTiO3 crystals and on strategies for defect-engineered oxide quantum wells, wires and dots

Recent Trends in Development of High Voltage Circuit Breakers with SF6 Alternative Gases

The available knowledge of state-of-the-art of SF6 alternative gases in switching applications was collected and evaluated in an initiative of the Current Zero Club together with CIGRE. The present contribution summarizes the main results of this activity and will also include the latest trends. The main properties and switching performance of new gases are compared to SF6. The most promising new gases are at the moment perfluoroketones and perfluoronitriles. Due to the high boiling point of these gases, in HV applications mixtures with CO2 are used. For MV insulation perfluoroketones are mixed with air, but also other combinations might be possible. The dielectric and switching performance of the mixtures, with mixing ratios that allow sufficiently low operating temperatures, is reported to be only slightly below SF6. Minor design changes or de-rating of switchgear are therefore necessary. Differences between the gas mixtures are mainly in the boiling point and the GWP

On the use of ion beams for the selection of radioactive waste matrices

The safe and long-term control of radioactive waste arising from nuclear power plants is one of the major challenges to the future use of nuclear energy. The evaluation of nuclear waste matrices relies on numerous conditions regarding the physico-chemical properties of the selected materials, such as resistance against oxidation or aqueous corrosion, stability in a radioactive environment, and ability to confine radioactive elements. Ion beams provide efficient tools for the evaluation of radwaste matrices since they allow to address three major issues: (i) the simulation of ion irradiation; (ii) the doping of the matrix with stable elements simulating the nuclei to be confined; and (iii) the characterization of the material by the use of nuclear microanalysis techniques. Illustrative examples are provided in the case of urania and zirconia

DC CONDUCTION OF EPOXY COMPOSITES UNDER COUPLED TEMPERATURE AND WATER UPTAKE EFFECTS

International audienc

Streamer and leader characterization in HFO1234ze(E) gas, in a divergent electric field

Abstract Pre-breakdown phenomena in HFO1234ze-(E) gas, considered as a potential replacement of SF6 for medium voltage insulation, are studied in needle-plane electrode systems versus pressure (0.01 to 0.3 MPa) under positive impulse voltage. Measurements are also carried out in air and SF6 in the same conditions for comparison. At the lowest pressure in HFO, the propagation of fast streamers is observed. Above 0.03 MPa, breakdown is the consequence of the propagation of stepped leaders, with shapes and velocities nearly identical to those observed in SF6. Several leader features (minimum inception voltage, propagation length) show that leader formation and propagation is easier in HFO compared to SF6. In turn, this allow explaining why breakdown voltages in HFO are slightly lower than in SF6

Partial Discharge Characterization Through Innovative Continuous Monitoring of Medium Voltage Substation

Partial discharges (PDs) are one of the key factors accelerating medium voltage (MV) equipment ageing. PDs can hence be used as an aging signature of MV switchgears. In a previous work [1], an innovative compact digital solution for PD continuous monitoring, based on capacitive coupling technology was presented. In this work, two main constraints of this monitoring device were assessed: having nonstandard IEC bandwidth and limited dataset. The application of this compact PD monitoring device has been then tested on multiple typical faults leading to PD in MV switchgears through experimental simulations in laboratory. A confirmation with state-of-the-art IEC compliant PD detector for Lab has been also performed. Results showed that the PD continuous monitoring system with nonstandard bandwidth and simplified data set is adapted to differentiate multiple types of PD sources in MV switchgears