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The correlation factor of impurity diffusion in body-centred cubic metals for mixed nearest- and next-nearest-neighbour monovacancy jumps

The correlation factor f2 of impurity diffusion in body-centred cubic metals is calculated assuming the competition of nearest- and next-nearest-neighbour monovacancy jumps. A four-frequency model in which only the impurity jump frequencies differ from those of the host atoms is considered. f2 is calculated as a function of temperature for different impurity migration energies and impurity masses. A comparison of f2 with experimental data shows qualitative agreement with the temperature function of the isotope effect for chromium diffusion in tungsten, thus supporting the hypothesis of high-temperature contributions of next-nearest-neighbour vacancy jumps in group V and VI metals.