Effect of SWCNT Dilution on the Resistivity of MgB 2
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Effect of SWCNT Dilution on the Resistivity of MgB2 Danhao Ma1, Ruwantha Jayasingha2, Dustin Hess3, Kofi W. Adu4,5, and Gamini U. Sumanasekera2,6 1
Department of Energy Engineering, The Pennsylvania State University, University Park, PA 16802, U.S.A. 2 Department of Physics & Astronomy, University of Louisville, Louisville, KY 40292, U.S.A. 3 Department of Physics, The Pennsylvania State University, University Park, PA 16802, U.S.A. 4 Department of Physics, The Pennsylvania State University, Altoona College, Altoona, PA 16802, U.S.A. 5 Materials Research Institute, Pennsylvania State University, University Park, PA 16802, U.S.A. 6 Conn Center for Renewable Energy Research, University of Louisville, Louisville, KY 40292, U.S.A.
Abstract We report an increase in superconducting temperature of magnesium diboride (MgB2) by minute single-wall carbon nanotubes (SWCNT) inclusions. The SWCNTs concentration was varied from 0.1wt% to 1.0wt%. The temperature dependence resistivity of sintered MgB2SWCNTs composites containing 0.1wt%, 0.5wt% and 1.0wt% were measured and compared with that of the pure MgB2. The superconducting critical temperature (Tc) of the MgB2 increased from 40 K to as high as 42.4 K for the MgB2 containing 0.5wt% of SWCNTs. The room temperature resistivity ratio (RRR) shows dependence on the sample composition. The temperature width (ΔT) decreases with increasing SWCNT content from 0.1wt% to 1.0wt%. The normal state resistivity data were fitted with the generalized Block-Grüneisen function obtaining a Debye temperature of ~ 900K. Introduction The past two decade witnessed the discovery of two fascinating and intriguing materials: single wall carbon nanotubes (SWCNT) and magnesium diboride (MgB2) that are still shaping our understanding of the superb properties of low dimensional systems and phonon mediated superconductivity, respectively. Carbon nanotube, a one-dimensional filamentous structure formed by seamlessly rolling a graphene sheet into tube was discovered by Iijima in 1991[1] and since then there has been an immense interest in its unique physical properties. There are vast reports on the resistivity of individual, bundles and mats/films of carbon nanotubes where it has been shown to exhibit quantum ballistic transport characteristics at low temperatures. Shown in Figure 1a insert, is a schematic representation of a SWCNTs bundle. The discovery of superconductivity in magnesium diboride (MgB2) at ~ 40K in 2001 by Akimitsu and co-workers[2] marked a new beginning of phonon mediated high temperature superconductivity materials, contrary to as thought previously. MgB2 has a simple AlB2-type crystallized structure with P6/mmm space group consisting of alternate hexagonal layers of Mg atoms and graphene-like honey comb B atoms with the Mg atoms located at the centers of the
hexagons of the B atoms[3,4] as shown as insert in Figure 1b. Much of the studies on the transport properties of the normal state above the superconducting temperature (Tc) have focused on resistivity of single crystals, films and
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