Enhanced critical current density at high magnetic fields in MgB2 with Ga/In acetylacetonate processed by spark plasma sintering

Abstract

Dense samples (94–96%) with starting composition (MgB2)0.99(X-acac)0.01 (X-acac denotes Ga or In acetylacetonate) were obtained by spark plasma sintering. The resulting material is a superconducting composite, where carbon substitutes for boron in the crystal structure of MgB2. Added samples show enhanced critical current density at high magnetic fields and this is reflected in high values of irreversibility field (Hirr) at temperatures below 25 K when compared to a pristine sample. More efficient is In-acac addition and it promotes a Hirr of ∼12.4 T (100 A/cm2 criterion) at 5 K. Carbon substitution for boron in the crystal structure of MgB2 has a strong influence on the pinning force and its related parameters and promotes in the added samples a grain boundary pinning mechanism as the dominant one, whereas the pristine sample with a low amount of carbon shows a major mechanism of point pinning type. However, our analysis indicates on the synergetic effects of the carbon substituting for boron and of the microstructural details on pinning and critical current density. The result strongly emphasizes the significantly different behavior of the additive during processing of the MgB2 samples, although thermal analysis experiments on both additives show very similar decomposition patterns.