Comparison of the Effect of Graphene and Graphene Oxide Doping on YBCO

Abstract

Weak-links in high temperature superconductors (HTS) are a result of an incorrect stoichiometric ratio found in grain boundaries and misaligned planes. These weak-links severely decrease the critical transport current of the bulk HTS material (such as YBCO) and increase resistance in the normal state. Bulk YBCO was doped with graphene oxide (GO) and reduced graphene oxide (rGO) in the following dopant concentrations: 0, 0.1, 0.5, 0.7, 0.9 and 1 % wt. Through mechanical hardness testing, it was observed that the hardness of the samples increased as the GO and rGO concentration increased. The 1 % wt. doped GO and rGO samples was observed to be hardest, with a true hardness of 2.630 GPa and 2.405 GPa respectively, compared to the control sample with a true hardness of 1.499 GPa. Critical transition temperature (TC ) of the GO doped YBCO samples are greater than rGO doped samples and is presumably related to the higher oxygen content found in GO. The 0.7 % wt. doping for GO and rGO samples had the highest critical transition temperature of 98 K and 91 K, respectively. Both GO and rGO samples showed a decrease in normal resistance up to 0.7 % wt. doping, compared to the control sample. The weak-link effect was most improved in the 0.7 % wt. doped samples for GO and rGO.