  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 un-reacted 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
non-uniform of around 3-10\mu m 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 (Tc). Both
AC and DC magnetization exhibited highest Tc at around 11.5 K for an NbC sample
with lattice parameter a = 4.471 {\AA}. The lower critical field (Hc1) and
irreversibility field (Hirr) measured at 3 K are around 250 Oe and 4.5 kOe
respectively. The upper critical field (Hc2) being determined from in-field AC
susceptibility measurements is 7.8 kOe and 11.7 kOe with 50% and 90%
diamagnetism criteria, respectively.
