Structure and Properties of MgB2 Bulks, Thin Films, and Wires

• Published in: IEEE transactions on applied superconductivity 2017-06, Vol.27 (4), p.1-5
• Main Authors: Prikhna, Tatiana A., Romaka, Vitaliy V., Shapovalov, Andrii P., Eisterer, Michael, Sokolovsky, Vladimir, Weber, Harald W., Grechnev, Gennadiy E., Boutko, Viktor G., Gusev, Alexander A., Kozyrev, Artem V., Goldacker, Wilfried, Moshchil, Viktor E., Sverdun, Vladimir B., Habisreuther, Tobias, Schmidt, Christa, Kovylaev, Valeriy V., Shaternik, Volodymyr E., Karpets, Myroslav V., Shaternik, Anton V.
• Format: Article
• Language: English
• Subjects: Boron; Boron alloys; computer simulation; critical current density; Critical current density (superconductivity); Magnetic fields; Microstructure; superconducting materials and thin films; Surface treatment; Wires
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2016.2638201

This paper describes the established correlations between the characteristics of MgB 2 -based superconducting materials and their structural features, in particular the oxygen distribution and content. As indicated by SEM and Auger analysis, a sizeable amount of oxygen is usually present in superconducting MgB 2 -based materials (bulks, thin films, and wires). The matrix phase of bulk MgB 2 contains rather small amounts of oxygen, but contains a high amount of dispersed inclusions or areas with compositions close to MgBO. X-ray phase analysis with Rietveld refinement (using the FullProf Suite program package) of several highly dense MgB 2 -based bulk samples (with high critical current densities) showed that the superconducting phase had a composition within the range MgB 1.68 O 0.26 and MgB 1.74 O 0.32 instead of pure MgB 2 . Besides, a small amount of a phase with MgO structure was observed in the materials by X-rays as well. The calculation of the enthalpy of formation confirms the possibility of oxygen solubility in MgB 2 and shows that the formation of MgB 1.75 B 0.25 is most favorable. The results of ab initio calculations of the electronic structure and stability of the MgB 2 compounds with partial oxygen substitution for boron show that it is energetically preferable for oxygen atoms to replace boron pairwise.