On the roles of graphene oxide doping for enhanced supercurrent in MgB₂ based superconductors

Abstract

Due to their graphene-like properties after oxygen reduction, incorporation of graphene oxide (GO) sheets into correlated-electron materials offers a new pathway for tailoring their properties. Fabricating GO nanocomposites with polycrystalline MgB2 superconductors leads to an order of magnitude enhancement of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel experimental approach to overcome the formidable challenge of performing quantitative microscopy and microanalysis of such composites, so as to unveil how GO doping influences the structure and hence the material properties. Atom probe microscopy and electron microscopy were used to directly image the GO within the MgB2, and we combined these data with computational simulations to derive the property-enhancing mechanisms. Our results reveal synergetic effects of GO, namely, via localized atomic (carbon and oxygen) doping as well as texturing of the crystals, which provide both inter- and intra-granular flux pinning. This study opens up new insights into how low-dimensional nanostructures can be integrated into composites to modify the overall properties, using a methodology amenable to a wide range of applications.

Improvements in the Dispersion of Nanosilver in a MgB2 Matrix through a Graphene Oxide Net

“…GO doping decreased RRR by about 35%, introducing the defects through carbon substitution. [2][3][4][5][6][7]26 GO + Ag co-doping decreases the value of RRR by about 50%. Ag nanoparticles were dispersed on GO sheets, making them much more effective in creation of defects, in addition to the defects introduced by the C released from surface of GO sheets.…”

“…Yeoh et al 6 have performed 3D atom probe tomography through the sample, and presented precise distribution of carbon and oxygen atoms, as well as location of individual GO platelets. From their study can be concluded that GO layers are uniformly dispersed in the MgB 2 matrix.…”

“…The smaller observed A F than for GO-doped MgB 2 is consistent with this picture (Table 2), as Ag nanoparticles also cause local grain misalignment. Based on our previous work, GO seems to provide a platform for uniform nucleation of MgB 2 grains, which has resulted in a remarkable improvement in the inter-grain connectivity with higher active cross section area (A F ) 6 . GO doping does not result in increased resistivity due to inter-and intra-band scattering, which would be expected for carbon-doping 8 .…”

“…Furthermore, recent researches present that GO doping even stimulate the growth of MgB 2 grains along preferred crystalline orientations 6,7 and improves the grain connectivity. It was also noticed that layered nano-sheets of GO are uniformly spread within and among the MgB 2 crystals 6 . This behaviour of GO in the MgB 2 matrix makes it suitable as a platform for more effective doping of MgB 2 by other (previously used) elements and compounds.…”

“…The incorporation of nano size carbon containing dopants such as SiC, carbon nanotubes (CNT), malic acid, graphene, and graphene oxide into this superconductor has been reported widely as being an effective means of improving the superconducting properties [2][3][4][5][6] . Most carbon dopants, however, have adverse effects on the critical temperature (T c ) and the low field J C performance.…”