Carbon Nanotube Doping Effect on Superconducting Properties of MgB2

A. SERQUIS; G. SERRANO; L. CIVALE; B. MAIOROV; J. KENNISON; M. JAIME; F. BALAKIREV

San Francisco

Simposio; 2006 MRS Spring meeting; 2006

Materials Research Society (MRS)

In the last years, several groups have achieved a substantial improvement of the transport properties of MgB2 in a magnetic field that is significantly larger than the low irreversibility field (Hirr) of the clean basic compound. Another interesting discovery was that the presence of two superconducting gaps allows tuning different upper critical fields (Hc2) by controlling different defect sublattices relative to orthogonal hybrid bands. Although the effect of carbon substitution was one of the most studied in MgB2, the results on C solubility and the effect of C-doping on the critical temperature (Tc) and critical current density (Jc>) reported so far vary significantly due to precursor materials, fabrication techniques and processing conditions used.  In this work we study the influence of single (S) and double wall (DW) carbon nanotubes (CNT) doping in the superconducting properties of MgB2 samples.  We have prepared polycrystalline samples with a nominal composition Mg(B1-xCx)2 (0<x<0.2), using CNT as a source of carbon. We characterized the microstructure and lattice parameters of samples by electron microscopy and X-ray diffraction. The magnetization properties were examined in a SQUID magnetometer. We used a 50 T mid-pulse magnet to perform four-probe transport measurements of Hc2(T) and Hirr(T).  We will present an analysis of the effect of C-doping size in the flux pinning and Hc2 properties based in the correlation of Tc, normal state resistivity, grain connectivity and C solubility.