The role of Pd over layer thickness on PLD YBCO coated conductor properties

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on the use of copper based substrates for ybco coated conductors

It is well known that the recrystallization texture of heavily cold-rolled pure copper is almost completely cubic. However, one of the main drawbacks concerning the use of pure copper cube-textured substrates for YBCO coated conductor is the reduced secondary recrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence of abnormal grains with unpredictable orientation) in pure copper substrate was observed within the typical temperature range required for buffer layer and YBCO processing (600–850 °C). To avoid the formation of abnormal grains the effect of both grain size adjustment (GSA) and recrystallization annealing was analyzed. The combined use of a small initial grain size and a recrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grains in pure copper tapes. Another way to overcome the limitation imposed by the formation of abnormal grains is to deposit a buffer layer at temperatures where secondary recrystallization does not occur. For example, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organic decomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrate underwent secondary recrystallization. Our experiments indicate that the motion of grain boundaries occurring during secondary recrystallization process does not affect the quality of LZO film

Effect of annealing on structure and superconducting properties in Fe(Se,Te)

Abstract In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure

Effect of oxygen contamination on densification of Fe(Se,Te)

Abstract The optimization of sintering behaviour of iron chalcogenides superconducting materials is mandatory to enhance their critical current density, in order to pursuit their application in the production of superconducting wires. In this context it has been investigated here the effect of oxygen contamination on the material densification, considering the issues related to industrial oxygen-free isolated production lines. Our results show that the densification process is negatively affected by oxygen contamination. However, despite the difference in density, all sintered samples are characterized by similar structural and morphological features, and show comparable electrical and magnetic properties, with low critical current densities (Jc<103 A/cm2). These results suggest that densification is not the key limiting factor in these conditions, and that grain boundary or misorientation factors may play a greater role in limiting the performance of sintered iron chalcogenides superconductors

Electrical resistivity and magnetic behavior of PdNi and CuNi thin films

Electrical and magnetic properties of sputtered Pd86 Ni14, Cu46 Ni54, and Cu42 Ni58 thin films have been investigated. Pd86 Ni14 shows clear ferromagnetic properties even if magnetic clusters of 4.6 μB are observed above the Curie-Weiss temperature, TCW. Different magnetic properties are observed in CuNi alloys. Below TCW, the field cooling susceptibility increases quasilinearly, while very large magnetic clusters, up to 10-12 μB, are observed above TCW. The temperature behavior of the resistivity of the thin films of the three alloys shows some common features. In particular, after a minimum the resistivity increases, probably due to the scattering of conduction electrons with Ni clusters. The temperature at which the minimum appears does not seem to depend on the host metal (Pd or Cu) and on the Ni concentration. These magnetic clusters affect the resistance behavior in the temperature range where the alloys are paramagnetic or close to their magnetic transition. © 2007 The American Physical Society

High-velocity instabilities in the vortex lattice ofNb/Permalloy Bilayers

We have studied the critical current density Jc for onset of vortex motion and the dynamic instability of the moving vortex lattice at high driving currents in superconducting (S)/ferromagnetic (F) Nb/Ni0.80Fe0.20 bilayers and in a single Nb film with the same thickness. The samples are all characterized by relatively high values of the pinning strength. The measured current-voltage characteristics are successfully described in the framework of the Larkin-Ovchinnikov model, modified in order to take into account the effect of the pinning close to the instability. We find that Jc is smaller in the S/F bilayers than in the single film and argue that this is due to the strongly inhomogeneous order parameter in the bilayers. Also, the critical velocity v* for the occurrence of the instability is found to be significantly larger in the S/F bilayers than in the single S layer. By extracting the quasiparticle energy relaxation rate from v*, we show that this effect is due to the same inhomogeneous order parameter and the resulting lower average value of the superconducting gap