We studied the influence of the disorder introduced in polycrystalline MgB 2 samples by neutron irradiation. To circumvent self-shielding effects due to the strong interaction between thermal neutrons and 10 B we employed isotopically enriched 11 B which contains 40 times less 10 B than natural B. The comparison of electrical and structural properties of different series of samples irradiated in different neutron sources, also using Cd shields, allowed us to conclude that, despite the low 10 B content, the main damage mechanisms are caused by thermal neutrons, whereas fast neutrons play a minor role. Irradiation leads to an improvement in both upper critical field and critical current density for an exposure level in the range 1 -2 ϫ 10 18 cm −2 . With increasing fluence the superconducting properties are depressed. An in-depth analysis of the critical field and current density behavior has been carried out to identify what scattering and pinning mechanisms come into play. Finally, the correlation between some characteristic lengths and the transition widths is analyzed.

No abstract

In this paper the feasibility of Fe(Se,Te) Coated Conductors (CC) on simple Rolling-Assisted Biaxilly Textured Substrate (RABiTS) template is studied. Starting from commercially available NiW5% tapes from Evico which have an out-of-plane orientation of about 6° and an in-plane orientation of 5.3°, a RABiTS template for Fe(Se,Te) coated conductors was realized depositing CeO2 thin films on the metallic tape. The oxide buffer layers, deposited via Pulsed Laser Ablation, have an out-of-plane and an in-plane orientation suitable for Fe(Se,Te) deposition and act as a chemical barrier against Ni diffusion. The Fe(Se,Te) deposited on such a simple template show a superconducting transition Tc of 18 K, very high upper critical field values with a Tc,0 of only 3 K in 18 T and self-field transport isotropic critical current values of 10 5 A/cm 2 at 4.2 K, which is reduced of less than one order of magnitude up to 16 T.

The introduction of artificial pinning sites in YBa2 Cu3O7−d (YBCO) epitaxial thin films has been\ud obtained by pulsed laser deposition ͑PLD͒ technique from YBCO-BaZrO3 ͑BZO͒ composite targets\ud with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, Tc , drop\ud observed in YBCO-secondary phase films grown by PLD has been successfully recovered by\ud increasing the deposition temperature. Transport properties analyses revealed improved pinning\ud force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an\ud anomalous dual peak structure which has been ascribed to the presence of two pinning\ud contributions. The crossover field, Bm , separating these two pinning regimes has been observed to\ud be temperature independent suggesting the occurrence of the matching field effect. The measured\ud value of Bm agreed with the matching field value, B⌽ = Knd⌽0 , as evaluated from transmission\ud electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making\ud YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below Bm in all\ud the temperature range inspected. On the contrary, in the high magnetic field range ͑above Bm͒, the\ud effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting\ud that at low temperatures the dominant pinning contribution arises from isotropic pinning centers

No abstract