Positive influence of ta addition on superconductive properties of high pressure synthesized MgB₂

Original · EN

Bulk MgB2 - based materials with the following critical current densities (jc) in 1 T field: 570 kA/cm² at 10 K, 350 kA/cm² at 20 K and 40 kA/cm² at 30 K and in 10 T field: 650 A/cm² at 10 K have been high-pressure (HP) synthesized from Mg and B with 2 - 10 wt.% addition of Ta. In synthesis and sintering process Ta plays the role of an absorbent of impurity gases (hydrogen, nitrogen, etc.) and forms Ta2H, TaH, TaN0.1, etc., thus promotes the reduction of MgH2 in Mg-B-O-matrix phase, as well as, the impurity nitrogen and oxygen in Mg-B grains (black MgB2 single crystals distributed over the matrix). Vickers microhardness of HP-synthesized material is Hv=12.54 (+/-)0.86 GPa (at 0.496-N load) The hardness (at 60-mN load) of MgB2 single crystals located in a sample matrix is 35.6 (+/-)0.9 GPa that is higher than the hardness of sapphire (31.1 (+/-)2.0 GPa).