S. Colombo

Extrinsic defect implantation in sintered YBCO slabs : magnetic and transport properties

This paper deals with proton irradiation effects on the intragrain and intergrain magnetic and transport properties of sintered YBCO. We have irradiated slab-shaped samples with beams at different fluences and energies, aiming at checking the possibility to modify in a planned way critical currents by means of proton implantation. Magnetic characterizations show enhanced intragrain pinning. Emphasis is given to the possibility to modulate intergrain magnetic properties by irradiation, determining critical current enhancement in optimal field and temperature ranges. Resistive measurements were performed in order to investigate the complex transport phenomena in polycrystalline materials, where superconducting and normal conduction mechanisms coexist. Irradiation-induced effects on both superconducting and normal state resistivity are studied. The addition of extrinsic defects leads to enhanced transport properties, emerging especially when a magnetic field is applied.

Intra and intergrain vortex excitations in proton implanted bulk YBCO slabs

Abstract The effects of proton induced defects on two different YBCO microstructures are investigated. Intragrain pinning is enhanced in dependence on fluence and temperature. Also implantation plays a significant role. Intergrain pinning is enhanced too, if the boundary grain structure shows an optimum connectivity.

Modulation of HTSC characteristics induced by proton irradiation

SummaryBulk slabs of sintered YBCO were irradiated with monoenergetic protons at different energies (3.5 and 6.5 MeV) and different fluences, ranging from 1.8·1016 to 8.6·1016 p/cm2. The effects on intergrain critical currents of protons crossing the sample and the effects of protons implanting in the specimen, has been studied by means of a.c. susceptibility characterizations. D.c. hysteresis cycles were measured in low fields in order to investigate the modifications in the intergrain critical current density due to proton implantation. The main result is the evidence that the intergrain Jc response to the applied field can be modulated by means of the proton irradiation. Resistive measurements were also performed in order to investigate the complex transport phenomena in polycrystalline materials. Irradiation-induced effects on both superconducting- and normal-state resistivity are studied. The addition of extrinsic defects can lead to enhanced transport properties, emerging especially when a magnetic field is applied.

Apparatus for transport characterisation of high-Tc superconductors

SummaryA full set of facilities for transport characterisation of HTS as well as a set of crucial measurements are presented which point out the possible sources of errors of the «home-made» apparatus. The main characteristics are the automatisation of the whole data acquisition, the appositely designed hardware and software with suitable error messages, the on-line statistical treatment of data, the possibility of on-line optimisation of the current pulses and finally the availability of quasi-static temperature conditions in the R vs. T curves. The d.c. four-point method with bipolar d.c. pulsed current is employed. The experimental techniques chosen to obtain specific metrological achievements are discussed.

Proton Irradiation Enhancement of Implanted Layers on Ceramic YBCO Bulk

In this work the possibility of enhancing the critical current density in proton implanted surface layers on YBCO bulk is discussed. A complete transport characterization shows that, for what concerns two samples from different irradiation runs, the critical current density has been enhanced. Increases of other meaningful parameters, such as average pinning energy and vortex-antivortex coupling strength, have also been found, although the relative effect of the implanted layer on the whole specimen cannot be evaluated in a fully quantitative way