▎ 摘　　要

In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in T-c. However for this sample, there is no significant improvement in H-c2 and H-irr. With the combined addition of GO and citric acid, the J(C)(H), H-c2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example J(C)(10 K, 5 T) of sample x = 10 has improved by a factor of similar to 15 as compared to pure MgB2 sample and by a factor of similar to 5.5 as compared to the x = 0 sample. Furthermore, H-c2(0) for x = 10 sample has enhanced by 13 T as compared to pure MgB2 while it has increased by similar to 10 T in comparison to x = 0 sample. Enhanced flux pinning has been observed with the combined addition of GO and citric acid. (C) 2014 Elsevier B.V. All rights reserved.