Effects of Sheath Materials, Doping and Thermo-mechanical Treatments on the Superconductivity

A. SERQUIS; G. SERRANO; D. RODRIGUES JR.; M. T. MALACHEVSKY; C. AYALA

Bruselas – 16-20 September 2007

Conferencia; EUCAS 2007; 2007

European Conference on Applied Superconductivity

Previous works indicate that a correlated enhancement of upper critical fields (Hc2) and criticalcurrent densities (Jc) was obtained by doping with SiC, single (SW) or double (DW) wall carbonnanotubes (CNT) in MgB2 bulk samples. In particular, CNT inclusions, with diameters close to the MgB2 coherence length (ξab(0) ~ 4-12nm, ξc(0) ~1.6-3.6 nm) are very good candidates for vortex pinning if they do not completely dissolve in the matrix but remain as tubes that can act as columnar defects, so it is interesting to study the effect of their alignment by rolling. In this work, different combinations of stainless steel, copper and titanium are used as sheath materials to fabricate SiC and DWCNT doped MgB2 wires and tapes by the powder-in-tube (PIT) method. The samples are cold deformed to the final dimension with several intermediate and final heat treatments between 400 and 900 C. The microstructure and phase composition of the tapes are followed during the deformation and heat treatment processes by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical temperatures (Tc), Jc and Hc2 are determined by magnetization and transport measurements. The correlation between the superconducting properties and the microstructural characteristics is discussed.