The point defect and diffusion properties of A15 Nb3Sn were investigated using ab initio density functional theory calculations and statistical thermodynamics. The defect structure was found to be of antisite type, with small amounts of Nb vacancies, and Sn vacancies showing a trend towards instability. Diffusion occurred mainly on the Nb-sub-lattice (restricted to intrachain jumps for both species), Sn-sublattice exchanges being unlikely for both species. In addition, ordering (disordering) was found to occur via Sn (Nb) jumps. The calculated Nb and Sn tracer diffusion coefficients exhibited a low sensitivity to the alloy composition around stoichiometry at 1000K , with DNb* ยป DSn* provided the correlation between atomic jumps was taken into account. Agreement with interdiffusion measurements was reached with reasonably low values for the geometrical correlation factor.
Atomic-Scale Study of Diffusion in A15 Nb3Sn. R.Besson, S.Guyot, A.Legris: Physical Review B, 2007, 75[5], 054105 (7pp)
Table 9
Diffusion Parameters for H in Nb-Ta Alloys at about 300K
Ta (at%) | Do (m2/s) | E (eV) |
0 | 4.2 x 10-8 | 0.136 |
10 | 4.52 x 10-8 | 0.140 |
25 | 3.8 x 10-8 | 0.146 |
50 | 5.5 x 10-8 | 0.165 |
75 | 4.2 x 10-8 | 0.140 |
90 | 1.9 x 10-8 | 0.100 |
100 | 1.9 x 10-8 | 0.091 |