Formation of nanostructure of magnesium diboride based materials with high superconducting characteristics
T.А. Prikhna1, A.Р. Shapovalov1,2, G.E. Grechnev3, V.G. Boutko4, A.A. Gusev4, A.V. Kozyrev1, M.A. Belogolovskiy2,5, V.E. Moshchil1, and V.B. Sverdun1
1V.Bakul Institute for Superhard materials NASU UKRAINE, 2, Avtozavodskaya Str., Kiev, 04074
2G.V. Kurdyumov Institute for Metal Physics National of the Sciences of Ukraine 36 Academician Vernadsky Blvd., UA-03680, Kiev-142, Ukraine
3B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine 47 Prospekt Nauky, Kharkiv 61103, Ukraine
4O.O. Galkin Donetsk Institute for Physics and Engineering NAS of Ukraine, Kyiv 03680, Ukraine
5Donetsk National University 21, 600-richya str., Vinnytsia, 21021, Ukraine pos Анотація:
Received February 9, 2016
The paper presents analysis of properties of bulk superconducting magnesium-diboride-based materials obtained by heating at high hydrostatic pressures (1–2 GPa), using methods of hot pressing (30 MPa) spark plasma sintering (16–96 MPa) and free sintering. It has been shown shown that the optimization of the distribution of impurities in MgB2 can be achieved by varying the synthesis conditions and introducing dopants. In particular, polycrystalline MgB2 material synthesized at 2GPa containing a high amount of impurity oxygen demonstrated high critical current densities (106 and 103 A/cm2 in the magnetic fields of 1 and 8.5 T, respectively, at 20 K). It is found that the oxygen impurity is mainly localized in homogeneously distributed in the matrix nanolayers or nanoinclusions which can act as pinning centers. Besides, the MgB2 matrix itself contains small amounts of dissolved oxygen. Impurity or specially added carbon entering the magnesium diboride structure leads to an increase in the critical magnetic fields to the values: Bc2 (22 K) = 15 T and Birr (18,5 K) = 15 T. The results of ab initio calculations of the electronic struc-ture and stability of the magnesium diboride compounds with partial substitution of oxygen or carbon for boron places showed that there are advantageous if carbon distributed in the structure of MgB2 homogeneously, but oxygen atoms replace boron sites by pairs in nearby positions or form zigzag chains.
PACS: 74.70.Ad Metals; alloys and binary com-pounds (including A15, MgB2, etc.); 74.20.Pq Electronic structure calculations; 74.62.Dh Effects of crystal defects, doping and substitution; 74.25.Sv Critical currents.
Key words: MgB2-based superconducting materials, electronic structure calculations, effect of doping on superconductive properties, critical superconductive current.