Browsing by Author "Khan, A"

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    Evaluation of isotopic boron (11B) for the fabrication of low activation Mg11B2 superconductor for next generation fusion magnets
    (John Wiley & Sons, Inc., 2020-04-13) Jie, H; Luzin, V; Zaman, M; Abdulsalam, AV; Chae, KH; Choi, H; Levchenko, VA; Nijhius, A; Kim, JH; Mustapić, M; Dou, SX; Yamauchi, Y; Khan, A; Hossain, A
    In this study, we analyze the properties of boron isotope (11B)‐rich powders from three different sources, that is, American, Cambridge, and Pavezyum, to fabricate the bulk Mg11B2 superconductors and evaluate their superconducting properties. While 11B‐rich powder is an essential precursor to fabricate Mg11B2 superconductors for fusion magnet applications, the properties of the 11B powder turned out to be critical to determine the quality of the final superconducting product. Therefore, appropriate control of processing conditions is needed to comply with the requirements of the nuclear fusion application. Analysis of the B isotope ratio by accelerator mass spectroscopy and neutron transmission revealed that all three types of powder are enriched with 11B to better than 99 at % quality. In addition, Pavezyum's 11B shows the lowest crystallinity and smallest crystalline domain size as evidenced by the high‐resolution X‐ray diffractometer and scanning electron microscopy. The chemical states of the boron isotope investigated with near edge X‐ray absorption fine structure spectroscopy and X‐ray photoemission spectroscopy also reveals that Pavezyum boron has amorphous structure. Mg11B2 bulks and multi‐filamentary (12‐filament) wires have been manufactured, sintered at different temperatures and characterized via the transport critical current density. The wire with Pavezyum 11B shows three times higher current carrying capacity at a particular magnetic field compared to the wire using Cambridge 11B and hence, Pavezyum 11B boron has the potential for manufacturing fusion grade Mg11B2 based magnets. The results of this study demonstrated that Boron powders with higher purity, smaller grain size and lower crystallinity are critical for improving the superconducting and electronic properties of Mg11B2 samples fabricated from the powder. Thus, the low‐neutron‐activation Mg11B2 is possibly an affordable and technically viable candidate to replace NbTi superconductors in the low field poloidal field and correction coils for the next‐generation fusion reactors. © 1999-2020 John Wiley & Sons, Inc.
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    YCa3(VO)3(BO3)4: a kagom compound based on vanadium(III) with a highly frustrated ground state
    (American Chemical Society, 2011-01-31) Miiller, W; Christensen, M; Khan, A; Sharma, N; Macquart, RB; Avdeev, M; McIntyre, GJ; Piltz, RO; Ling, CD
    A new S = 1 kagomé compound based on vanadium(III) is reported. The structure was refined simultaneously against single-crystal neutron and X-ray diffraction data, as a gaudefroyite-type with a new supercell (a′ = 2a + b, b′ = −a − 2b, c′ = c) driven by the ordering of columns of isolated triangular BO3(3)− ions. Low-temperature neutron powder diffraction and magnetic (dc and ac susceptibility) data rule out the presence of long-range magnetic order above at least 1.5 K, but specific heat data suggest that the ground state involves short-range magnetic order, which is frustrated by the coexistence/competition of FM and AFM correlations, together with the characteristic geometric frustration of the kagomé lattice. Magnetic susceptibility data rule out a spin-glass state, pointing to an exotic ground state comparable to the spin-ice or spin-liquid states. This makes YCa3(VO)3(BO3)4 one of the most highly frustrated experimental realizations of the kagomé lattice yet discovered. © 2011, American Chemical Society