  We have performed density functional calculations of the formation energies
of substitutional transition metal (TM) defects, C vacancies, and C
interstitial defects in TiC. In addition we have evaluated the migration energy
barriers for C atoms in the presence of TM impurities. We find that the
solubility of TM impurities taken from the 3d TM series is low and only Sc and
V impurities can be dissolved into TiC at equilibrium. In addition, we find
that the migration energy barriers of C in TiC are greatly affected by the
presence of TM impurities: The migration barriers are generally lower in the
presence of impurities compared to pure TiC and show a clear dependence on the
atomic size of the TM impurities. We propose that the mobility of C in TiC will
be the highest in the presence of TM impurities from the middle of the 3d TM
series.
