Phenomenological coefficients for transport by dumbbell mechanisms in a dilute random bcc alloy

Onsager phenomenological coefficients for matter transport are calculated f or models of interstitial dumbbell jump mechanism appropriate to dilute bin ary bce transition-metal alloys. By use of a refinement of a kinetic equati on method earlier employed for dilute and concentrated fee alloy models, th e linear response expressions are reduced to expressions containing defect jump frequencies and concentrations and certain Brillouin integrals. An exa mple of the final form for the case where one particular mechanism operates alone is described in more detail. Monte Carlo simulation results are in s atisfactory agreement with the theoretical predictions. Comparison is also made with the pair association calculations by Barbu and Lidiard (1996, Phi l. Mag. A, 74, 709). It is shown that, even when all mechanisms operate sim ultaneously, simple relationships exist between parts of the three independ ent phenomenological coefficients. The relationship to the earlier calculat ion of the impurity and defect coefficients is also discussed.