  The problem of estimation of the tracer diffusion coefficients is solved by
utilizing a novel tracer-interdiffusion couple technique even in the absence
suitable radioisotope of one of the components and absence of reliable
thermodynamic parameters. This is demonstrated by generating reliable and
reproducible mobility data in the alloys of the Fe-Ga system with a strong
composition dependence of the diffusion coefficients. Tracer- (59Fe) and
inter-diffusion are simultaneously measured in three couples Fe/Fe-16Ga,
Fe/Fe-24Ga and Fe-16Ga/Fe-24Ga at 1143 K. The results obtained for the couples
with different end-members are in an excellent agreement with each other for
the overlapping composition intervals. The influence of the molar volume on the
measured tracer- (59Fe) and inter-diffusion coefficients is evaluated. Using
thermodynamic calculations, the Ga tracer diffusion coefficient and the vacancy
wind factor are determined via the Darken-Manning relation for the composition
range of 0-24 at.% Ga. The results confirm the reliability of the
tracer-interdiffusion couple technique for producing highly accurate diffusion
data, in the present case for optimizing the mobility description of the bcc
phase of the Fe-Ga system. The Ga tracer diffusion coefficients are further
estimated via experimental determination of the ratio of the Fe and Ga tracer
diffusivities at the Kirkendall marker planes and utilizing the Fe tracer
diffusion coefficients measured directly by the radiotracer method.
