The tracer diffusion coefficient of Fe (table 12) and the chemical diffusion coefficient (table 13) in L12-ordered Pt3Fe were measured at temperatures below the order-disorder transition. The diffusion of Fe could be described by:

23.3mol%Fe:     D (m2/s) = 4.21 x 100 exp[-454(kJ/mol)/RT]

25.2mol%Fe:     D (m2/s) = 2.10 x 10-1 exp[-418(kJ/mol)/RT]

26.4mol%Fe:     D (m2/s) = 2.68 x 10-3 exp[-369(kJ/mol)/RT]

and the chemical diffusion could be described by:

D (m2/s) = 1.86 x 10-5 exp[-293(kJ/mol)/RT]

The tracer diffusion coefficient of Fe in a nearly stoichiometric alloy curved upwards, in the Arrhenius plot, upon approaching the order-disorder transition temperature. The chemical diffusion coefficient was some 10 to 30 times higher than the diffusion coefficient of Fe. The tracer diffusion coefficient was affected by the composition: it increased with increasing Fe concentration through the stoichiometric composition, but this trend almost vanished at higher temperatures. The chemical diffusion coefficient was essentially independent of composition. The tracer diffusion coefficient of Pt was

estimated from the Darken-Manning relationship. At 1223K, it was between the chemical diffusion coefficient and the tracer diffusion coefficient of Fe.

Tracer and Chemical Diffusion in L12-Ordered Pt3Fe. Y.Nosé, T.Ikeda, H.Nakajima, H.Numakura: Materials Transactions, 2003, 44[1], 34-9

 Table 13

 Chemical Diffusivity of Fe in Pt3Fe