Higher Borides and Oxygen-Enriched Inclusions as Possible Pinning Centers in MgB${_2}$-Based Superconducting Materials

A. V. Kozyrev$^{1}$, T. A. Prikhna$^{1}$, P. P. Barvitskyi$^{1}$, A. V. Shaternik$^{1}$, V. E. Shaternik$^{2}$

$^{1}$V. M. Bakul Institute for Superhard Materials, NAS of Ukraine, 2 Avtozavodska Str., UA-04074 Kyiv, Ukraine
$^{2}$G. V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine

Received: 02.05.2019. Download: PDF

An experimental study of the effect of titanium additives (metal, polyvalent oxide and carbide) and silicon carbide on the formation of phases and structure of MgB${_2}$-based superconducting materials obtained from magnesium and boron powders under high pressures and temperatures (2 GPa, 800–1050°C), is performed. As found, the presence of titanium and silicon carbide promotes the oxygen segregation. At the increasing of synthesis temperature to 1050°C, this leads to the formation of a large number of nanoscale inclusions that can work as pinning centres. In addition, titanium binds hydrogen, which prevents the formation of magnesium hydride. The addition of titanium oxide leads to the formation of a large amount of magnesium oxide phase (up to 25% wt.), but titanium, as in the case of pure metal powder, still binds hydrogen. In addition to the formation of nanoscale oxygen-rich inclusions, dopants also cause a change in distribution of higher boride phases—their number increases and the size decreases up to values comparable to the coherence length, so, a significant part of them can be pinning centres. This effect is especially noticeable with titanium (1050°C), but is also observed in the presence of silicon carbide. Due to the increase in the number of pinning centres, the doping with titanium and silicon carbide can significantly increase the critical current density in the bulk MgB${_2}$-based superconducting materials. During the synthesis from magnesium and boron powders mixture (boron contains 1.5% wt. oxygen) at 2 GPa and 1050°C, the addition of 10% wt. titanium increases the critical current density at 20 K and 0 T from 4$\cdot10^{5}$ to 7$\cdot10^{5}$ А/сm$^{2}$. In the same case of silicon carbide (boron contains 0.66% wt. oxygen), the critical current density increases from 9$\cdot10^{5}$ to 13$\cdot10^{5}$ А/сm$^{2}$.

Key words: magnesium diboride, bulk superconductor, pinning centres, critical current density, thermobaric synthesis.

URL: http://mfint.imp.kiev.ua/en/abstract/v41/i07/0863.html

DOI: https://doi.org/10.15407/mfint.41.07.0863

PACS: 64.60.My, 64.70.K-, 64.75.g-, 74.25.Wx, 74.62.Bf, 74.62.Dh

Citation: A. V. Kozyrev, T. A. Prikhna, P. P. Barvitskyi, A. V. Shaternik, and V. E. Shaternik, Higher Borides and Oxygen-Enriched Inclusions as Possible Pinning Centers in MgB${_2}$-Based Superconducting Materials, Metallofiz. Noveishie Tekhnol., 41, No. 7: 863—871 (2019) (in Russian)

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