A MICROSTRUCTURAL INTERPRETATION OF MAGNETIC-RELAXATION IN HIGH-TEMPERATURE SUPERCONDUCTORS - APPLICATION TO YBA2CU3O7-DELTA TWINNED AND DETWINNED SINGLE-CRYSTALS

Magnetic relaxation experiments with YBa2Cu3O7-delta (YBCO) twinned and detwinned single crystals are interpreted in such a way that a clear correlation between the kinetics of relaxation and microstructure can be proposed. It is shown that theoretical fits to the non-logarithmic kinetics observed at higher temperatures can be used to evaluate the density of isolated strong-pinning regions in these crystals as well as the rate of escape of vortices from pinning centres. The pinning centre density obtained is consistent with the expected density of ordered oxygen vacancy domains in YBCO, which may act as strong pinning centres. The time-logarithmic kinetics observed at lower temperatures can be associated with the existence of extended pinning agglomerates (along twin boundaries, for example). The model adopted in the analysis is general and can be applied to other superconductors.8314815

NOVEL ON-BOARD PROCESSING ARCHITECTURES FOR SATELLITE SPREAD-SPECTRUM COMMUNICATIONS

At present, there is a drive to establish some form of on-board signal processing in satellite communication systems. Further, spread spectrum techniques can, in some cases, be an attractive contender for the multiple access scheme. This paper discusses a novel implementation of the spread spectrum correlator, using high temperature superconducting technology, which is well-suited to space payloads. In addition the various design constraints and benefits are examined. The paper then reports on the experimental results obtained using a copper-based prototype device operating in the C-band region with a spreading code rate of up to 500 Mbit/s

THE LOW FIELD SIMULATION AND STUDY OF MAGNETIZATION IN HIGH-TC SUPERCONDUCTORS AT 77K

The magnetization of different samples of BiSCCO superconductor have been studied at low fields and the hysteresis loops obtained compared with a numerical simulation. The numerical simulation is used to provide details of the field dependence of the critical current density, which would be impossible to obtain by an analytical interpretation of the data

FLUX-CREEP IN HIGH-TEMPERATURE SUPERCONDUCTORS IN LOW FIELDS AT 77K

A technique that allows the flux-creep of bulk superconductors to be studied has been developed. This technique has been applied to the measurement of flux-creep in samples of lead doped BiSCCO 2223 that have undergone a variety of processing routes

THE LOW FIELD SIMULATION AND STUDY OF MAGNETIZATION IN HIGH-TC SUPERCONDUCTORS AT 77K

The magnetization of different samples of BiSCCO superconductor have been studied at low fields and the hysteresis loops obtained compared with a numerical simulation. The numerical simulation is used to provide details of the field dependence of the critical current density, which would be impossible to obtain by an analytical interpretation of the data

Microstructural and microwave characterisation of low temperature processed Tl2Ba2Ca1Cu2Ox thin films

Tl2Ba2Ca1Cu2Ox thin films on LaAlO3 with excellent alignment suitable for the fabrication of passive microwave devices operating at 77K are fabricated using an ex-situ anneal step in argon atmospheres at temperatures of 720 - 740 degrees C, In order to understand the factors influencing their microwave and transport properties, the microstructure and compositions of the films have been examined by TEM, HREM and SEM and correlated with the R-s measurements obtained by the partial-end-wall-replacement technique

THERMAL-SHOCK RESISTANCE AND BENDING STRAIN TOLERANCE OF ELECTROPHORETICALLY DEPOSITED BI2SR2CACU2OY/AG TAPES

The degradation in 77 K self-field critical current density (Jc) of electrophoretically deposited Bi-2212/Ag tapes has been evaluated separately for thermal cycling (320-77 K), bending in compression, tension and combined compression-tension. After 11 repetitions of 320-77 K thermal cycles, (Jc) is reduced to 75-80% of its original value. A greater number of cycles resulted in no further degradation. The bending strain tolerance depends not only on bending strain, but also on the thickness of superconducting layers and the sense of bending. The superconducting layers show greater tolerance to compressive than tensile bending strain. Strain tolerance increases as layer thickness decreases. 13 μm layers can withstand strain of 0.2% without degradation in (Jc). © 1995