Diffusion in heterogeneous biphase structures

The present paper deals with the determination of temperature dependence of the effective diffusion coefficient in heterogeneous biphase structures using diffusion coefficients measured in both phases and the short-range order parameter. A new interpretation of this short-range order parameter is given as the relative volume of the ordered structure in the sample,V _(ord)/V.For the AuCu₃ alloy, the lacking values of the Au diffusion coefficients at temperaturesT<760 K in the partially ordered structure of this alloy were calculated on the basis of long-range order parameter values and diffusion characteristics which are valid for the perfectly ordered or disordered structures, respectively. For solid solutions of theAB andAB ₃ type the relation between the long and short-range parameters is given; numerical calculations of short-range order parameters were carried out for -brass and for the Cu₃Au alloy with the use of long-range order parameters and heats of formation.An explanation of the diffusion anomaly in ferromagnetic materials close to the Curie temperature is given and the temperature dependence of the relative volume of the paramagnetic phase in -iron is calculated.ikova 22, Brno, Czechoslovakia.The author wishes to express his thanks to Professor L. M. Slifkin for providing a xerox-copy of a part of Mr. Alexander's thesis 15] which facilitated the evaluation of diffusion characteristics in Cu₃Au alloy, and to Mr. M. Szob for recalculating some equations.