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End date: 2019 × Start date: 2010 × Type: Text × Subject: Konferenzschrift × Subject: Magnesium diborides × WGL Institute: IPHT ×

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    Superconductivity in multi-phase Mg-B-O compounds
    (Amsterdam [u.a.] : Elsevier, 2012) Prikhna, T.; Gawalek, W.; Eisterer, M.; Weber, H.W.; Noudem, J.; Sokolovsky, V.; Chaud, X.; Moshchil, V.; Karpets, M.; Kovylaev, V.; Borimskiy, A.; Tkach, V.; Kozyrev, A.; Kuznietsov, R.; Dellith, J.; Shmidt, C.; Basyuk, T.; Litzkendorf, D.; Karau, F.; Dittrich, U.; Tomsic, M.
    Structures of MgB2-based materials manufactured under pressure (up to 2 GPa) by different methods having high superconducting performance and connectivity are multiphase and contain different Mg-B-O compounds. Some oxygen can be incorporated into MgB2 and boron into MgO structures, MgBx (X=4-20) inclusions contain practically no oxygen. Regulating manufacturing temperature, pressure, introducing additions one can influence oxygen and boron distribution in the materials and thus, affect the formation, amount and sizes of Mg-B-O and MgBx inclusions and changing type of pinning, pinning force and so affect critical current density jc. The boron concentration increase in initial Mg and B mixture allows obtaining sample containing 88.5 wt% of MgB12 with Tc of 37.4 K (estimated magnetically).
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    Structure and superconducting characteristics of magnesium diboride, substitution of boron atoms by oxygen and carbon
    (London [u.a.] : Institute of Physics, 2017) Prikhna, Tetiana; Romaka, Vitaliy; Eisterer, Michael; Shapovalov, Andrii; Kozyrev, Artem; Grechnev, Gennadiy; Boutko, Viktor; Goldacker, Wilfried; Habisreuther, Tobias; Vakaliuk, Oleksii; Halbedel, Bernd
    An x-ray analysis of MgB2-based materials shows that they contain MgB2 and MgO phases. According to a quantitative Auger analysis (taken after removing the oxidized surface layer by Ar ion etching in the microscope chamber) the MgB2 phase contains some amount of oxygen that approximately corresponds to the composition MgB2.2-1.7O0.4-0.6. Rietveld refinement of the MgB2 phase, based on EDX data with varying B/O content, leads to the composition MgB1.68-1.8O0.2-0.32. Ab-initio modelling of boron substitution by oxygen in MgB2 (ΔH f = -150.6 meV/atom) shows that this is energetically favourable up to the composition MgB1.75O0.25 (ΔH f = -191.4 meV/atom). In contrast to carbon substitution, where very small levels of doping can dramatically affect the superconducting characteristics of the material with concomitant changes in the electron density, oxygen substitution results in very little change in the superconducting properties of MgB2. The formation of vacancies at the Mg site of both MgB2 and substituted MgB1.75O0.25 was modelled as well, but has shown that such processes are energetically disadvantageous (ΔHf of Mg0.875B2 and Mg0.75B1.75O0.25 are equal to -45.5 and -93.5 meV/atom, respectively).