Temperature Dependent Thermopower and Resistance Measurements of CNT-MgB2 Composites

ABSTRACTThe temperature dependent resistance R(T) and thermopower S(T) of sintered single wall carbon nanotubes (SWCNT) and magnesium diboride (MgB2) composites containing 5wt%, 10wt%, and 15wt% of SWCNTs have been measured and compared to their pure counterparts. The thermopower of both MgB2 (in the normal state) and SWCNT remain positive over the entire temperature range (10K to 300K) with room temperature values being ∼ 8μV/K and 57μV/K, respectively. The thermopower of the sintered composites decreased with decreasing temperature and switched from positive to negative near 70K. The superconducting critical temperature (Tc) of the samples ranges from 38K-41K. The room-temperature resistance ratio (RRR) is seen to depend on the sample composition. The temperature width (ΔT) is observed to increase with increasing SWCNT concentration. The normal state resistance data were fitted with the generalized Block-Grüneisen function obtaining Debye temperature of ∼ 900K.

SUPERCONDUCTING PROPERTIES OF MgB2 COMPOSITES CONTAINING TYPE I SUPERCONDUCTING METALS

We have examined superconducting property of MgB 2, containing Type 1 elemental superconductor, Pb . The results showed double transition temperatures of superconductivity. Although the addition of Pb considerably improved grain connectivity of MgB 2, the presence of Type I superconducting phase ( Pb ) degraded the superconductivity of composites by flux creep.