A MODIFIED THERMODYNAMIC MODEL FOR THE IMPURITY DIFFUSION VIA NEAREST-NEIGHBOR AND NEXT-NEAREST-NEIGHBOR JUMPS IN BODY-CENTERED-CUBIC METALS OF THE GROUP-V AND GROUP-VI

A modified thermodynamic model (T-m-model) for the impurity diffusion in group V and VI metals is developed, which takes into account neares t-(NN) and next-nearest (NNN) neighbour monovacancy jumps. The correla tion factor f is separately calculated with the aid of Monte-Carlo sim ulation. The calculation of f is based on a nineteen-frequency model f or mixed NN and NNN jumps. The comparison of calculated and experiment al diffusion coefficients reveals good agreement for several systems. On the other hand, it becomes obvious that the T-m-model is not applic able to the diffusion of group VIII metals in metals of the groups V a nd VI.