N. Novikov | Searcharxiv

arXiv2002

Positive influence of ta addition on superconductive properties of high pressure synthesized MgB_2

Bulk MgB2 - based materials with the following critical current densities (jc) in 1 T field: 570 kA/cm^2 at 10 K, 350 kA/cm^2 at 20 K and 40 kA/cm^2 at 30 K and in 10 T field: 650 A/cm^2 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).

cond-mat.supr-con↗

arXiv2002

Soldering of MT-YBCO: method to produce superconductive junctions

A method of soldering of melt-textured YBa2Cu3O7-d -based (MT-YBCO) superconductive blocks using a TmBaCu3O7-d (Tm123) powder has been suggested. The method excludes stages of slow cooling during soldering and preparation of auxiliary layers. To estimate the critical current density (jc) through the obtained junction, we have drilled rings from single-domained MT-YBCO blocks, cut into two pieces along the diameters and soldered using a Tm123 powder. The critical current density, jc, (estimated using vibrating sample magnetometer) through the soldered ring was 34 kA/cm^2 in 0 T field at 77 K, which turned out to be even higher by a factor of approximately 1.5 than that through the single-domained material. The increase in jc through the soldered ring has been observed up to the 2.5 T field, while in the higher fields some decrease of jc took place. As a result of the field mapping of the trapped magnetic flux in soldered ring using a Hall probe, we obtained a regular truncated cone and the maximal level of trapped field for the ring 8 and 4 mm in outer and inner diameters was about 80 mT.

cond-mat.supr-con↗