Article

Vacuum Encapsulated Synthesis of 11.5 K NbC Superconductor

Journal of Superconductivity and Novel Magnetism (Impact Factor: 0.91). 05/2012; 25:1421–1425. DOI: 10.1007/s10948-012-1654-6
Source: arXiv

ABSTRACT

Bulk polycrystalline NbC samples are synthesized through solid state reaction route in an evacuated sealed quartz tube. Studied NbC samples are crystallized in NaCl-type cubic structure with space group Fm-3m. To control cell parameters and minute unreacted phases, different samples are synthesized with various heat treatments. Finally, phase pure NbC is achieved. The grain size of the as systemized material being seen from SEM (scanning electron microscopy) is nonuniform of around 3–10 µm size. Crystal structure and lattice parameters of samples have been calculated by Rietveld analysis of room temperature X-ray powder diffraction data. The lattice parameter increases with synthesis temperature and scales with superconducting transition temperature (T
c
). Both AC and DC magnetization exhibited highest T
c
at around 11.5 K for an NbC sample with lattice parameter a=4.471 Å. The lower critical field (H
c1) and irreversibility field (H
irr) measured at 3 K are around 250 Oe and 4.5 kOe, respectively. The upper critical field (H
c2) being determined from in-field AC susceptibility measurements is 7.8 kOe and 11.7 kOe with 50 % and 90 % diamagnetism criteria, respectively.

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    • "The crystal structure typically changes with the content of interstitial non-metal atoms, as exhibited by e.g. Cr-N, Ti-N, Fe-N, V-N and Nb-C systems [1] [2] [3] [4] [5] [6] [7] [8] [9]. When the occupancy of octahedral interstices is relatively low (for example, less than 50%), the metal atoms tend to form a hexagonal structure [4,7–8,10]. "
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