Enhancing the superconducting temperature of MgB2 by SWCNT dilution

• Published in: Physica. C, Superconductivity Vol. 497; pp. 43 - 48
• Main Authors: Ma, Danhao, Jayasingha, Ruwantha, Hess, Dustin T., Adu, Kofi W., Sumanasekera, Gamini U., Terrones, Mauricio
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-02-2014; Elsevier
• Subjects: Carbon nanotubes; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Effects of crystal defects, doping and substitution; Exact sciences and technology; Magnesium diboride; Mesoscopic and nanoscale systems; Nonsubstitutional hole-doping; Physics; Superconducting films and low-dimensional structures; Superconducting temperature; Superconductivity; TC enhancement; Transition temperature variations; Carbon nanotubes; Superconducting temperature; Magnesium diboride; Nonsubstitutional hole-doping; TC enhancement; Raman spectra; Electrical conductivity; Solid inclusion; Hole density; Superconducting transitions; XRD; enhancement; Field emission electron microscopy; Singlewalled nanotube; Nanocomposites; T; Magnesium boride; Temperature effects; High-Tc superconductors; Microstructure; Charge transfer
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2013.09.017

•We demonstrate an increase in TC of MgB2 without appealing to chemical substitution.•The increase in TC is attributed to hole-doping of the MgB2 via charge transfer.•This leads to the softening of the E2g phonon and an enhancement of the DOS at the Fermi level.
We report, for the first time, an increase in the superconducting critical temperature, TC of commercial “dirty” MgB2 by a nonsubstitutional hole-doping of the MgB2 structure using minute, single-wall carbon nanotube (SWCNT) inclusions. We varied the SWCNTs concentration from 0.05wt% to 5wt% and investigated the temperature-dependent resistivity from 10K to 300K. We used micro-Raman spectroscopy, field-emission scanning electron microscopy, and X-ray diffraction to analyze the interfacial interactions between the SWCNTs and the MgB2 grains. We obtained an increase in TC from 33.0 to 37.8K (ΔTC+=4.8K), which is attributed to charge transfer from the MgB2 structure to the SWCNT structure. The charge transfer phenomenon is confirmed by micro-Raman analysis of the phonon states of the SWCNT tangential band frequency in the composites. We determined the charge transfer per carbon atom to be 0.0023/C, 0.0018/C and 0.0008/C for 0.05wt%, 0.5wt% and 5wt% SWCNT inclusions, respectively, taking into account the contributions from the softening of the lattice constant and the nonadiabatic (dynamic) effects at the Fermi level. This report provides an experimental, alternative pathway to hole-doping of MgB2 without appealing to chemical substitution.