The self-diffusion of 14C in NbCx single crystals was measured as a function of composition at 1900 to 2315K, and could be represented by:

NbC0.868:     D(cm2/s) = 2.59 exp[-100.42(kcal/mol)/RT]

NbC0.834:      D(cm2/s) = 7.44 exp[-105.0(kcal/mol)/RT]

NbC0.766:      D(cm2/s) = 2.22 x 10-2 exp[-76.02(kcal/mol)/RT]

The lower values of the activation energy and the pre-exponential term in NbC0.766 were attributed to a change in the path of C mass transport.

B.B.Yu, R.F.Davis: Journal of Physics and Chemistry of Solids, 1979, 40[12], 997-1006