[en] Epitaxial titanium diboride thin films have been deposited on sapphire substrates by pulsed laser ablation technique. Structural properties of the films have been studied during the growth by reflection high energy electron diffraction (RHEED) and ex-situ by means of X-ray diffraction techniques; both kinds of measurements indicate a good crystallographic orientation of the TiB₂ film both in plane and along the c axis. A flat surface has been observed by atomic force microscopy imaging. Electrical resistivity at room temperature resulted to be five times higher than the value reported for single crystals. The films also resulted to be very stable at high temperature, which is very promising for using this material as a buffer layer in the growth of magnesium diboride thin films

[en] This book covers the proceedings of the 3rd National Meeting on High Temperature Superconductivity Topics includes: Crystal growth of superconductors; thermodynamic stability of superconducting materials; spectroscopy of High Tc Superconductors; synchrotron radiation investigation of superconductors; density state determination; measurements of current density; preparation and characterization of superconductors

[en] Critical fields of four MgB₂ thin films with a normal state resistivity ranging from 5 to 50 μΩ cm and T_c from 29.5 to 38.8 K were measured up to 28 T. H_c2(T) curves present a linear behavior towards low temperatures. Very high critical field values have been found, up to 24 T along the c-axis and 57 T in the basal plane not depending on the normal state resistivity values. In this paper, critical fields will be analyzed taking into account the multiband nature of MgB₂; we will show that resistivity and upper critical fields can be ascribed to different scattering mechanisms

[en] Nb₃Sn commercial wires (diameter 0.5 mm, 3700 filaments) have been hydrogen doped at various concentrations and the superconducting properties of these wires have been correlated to the hydrogen content x in Nb₃SnH /SUB x/ . Here the results are presented which regard critical temperature and overall critical current density for applied fields from 9 T to 12 T at 4.2K and 6K for hydrogen content up to x = 0.310. The critical temperature trend shows a slight maximum at x approx. = 0.02, after which it decays abruptly. Also the critical overall current density at same hydrogen concentration is higher than that of unhydrogenated samples at 4.2 K and is comparable or better at 6 K. The resulting dJ /SUB ov/ /dB shows a good behaviour in the studied field range

[en] Laboratory scale ternary alloys Nb-43 wt % Ti-25 wt% Ta, Nb-38 wt % Ti-34 wt % Ta, Nb-51 wt % Ti-14.7 wt % Ta were prepared. The alloys exhibit excellent ductility and thus no problems arise during production and handling of the cables. As for the Nb-Yi alloys, an increase of intermediate cold-work degree; also for ternary alloys, leads to better superconducting properties. After adequate optimization, the Nb-38 wt % Ti-34 wt % Ta alloy shows the best superconducting properties and, at 12 Tesla and 2.15K, Jsub(c)=600A/mm² can be reached

[en] In this paper the authors report results on the growth of borocarbides ErNi₂B₂C and DyNi₂B₂C thin films by an ultra high vacuum laser ablation technique. The dependence of the film structure and properties on the deposition parameters has been studied. Moreover the possibility to obtain superconducting films with a tungsten buffer layer on MgO substrates has been successfully checked. Here the authors present details on the deposition procedure as well as on the structural, morphological, and physical characterization

[en] The behaviour in a magnetic field of YBa₂Cu₃O_7-y sintered samples is described. A.C. susceptibility and magnetization measurements on samples with different geometries are reported. The results show in addition to a macroscopically superconducting behaviour the presence, for magnetic filds large enough, of superconducting grains separated by regions of meterial in a normal state. All the experimental results will be described in these terms. The intra-grain critical currents as well as the inter-grains ones, which are much lower, are described

[en] Quantum Hall effect measurements on commercial low-mobility n-channel MOSFETs have been performed. The channel resistance vs. electron concentration has the expected oscillating behaviour and gives the quantized values for the Hall resistance, at least in the region of higher mobility. One class of the tested samples gave a surprising behaviour, both in QHE and in field effect mobility measurements: this is thought to be due to uncontrolled differences in the diffusion zones at the interface between the channel and the contacts. In particular, it is attributed the deformation of the QHE curves to the onset of a thermoelectromotive force which is present in the electron gas even if the sample is isothermal. A clear evidence for thermoelectric effects is given by measurements made on a high-quality Hall geometry MOSFET

[en] In this paper they present magnetoresistivity and Hall effect measurements performed on a YBCO epitaxial film as a function of the angle θ between the external magnetic field and the a-b planes. The resistivity and Hall effect measurements are analyzed in term of the general scaling approach proposed by Blatter and coworkers; the Hall conductivity data are examined to separate the contributions due to vortices and quasi particles

[en] A novel magnetic procedure has been introduced for the determination of the degree of texturing of the superconducting grains in Ag-sheathed (Bi,Pb)₂Sr₂Ca₂Cu₃O_x tapes. Our new method is based on the observation that, in the BSCCO family of superconductors, a relevant anisotropy is present between the in-plane and out-of-plane critical current densities of individual crystallites. By neglecting the magnetic moment of the single grain due to out-of-plane circulating currents, and by comparing magnetic hysteresis loops measured within different field orientations with respect to the tape direction, it has been possible to determine the average degree of texture of an assembly of BSCCO superconducting grains. As a result of our simple approach, we have measured the texture evolution of the precursor grains during the cold deformation process of unreacted multifilamentary (Bi,Pb)₂Sr₂Ca₂Cu₃O_x tapes; moreover, we have been also able to distinguish between longitudinal and transverse texture of the grains with respect to the tape direction. Finally, the usefulness of our method has been verified on tapes prepared with various precursor powders and cold deformation techniques. (author)