Diffusion mechanisms in b.c.c. metals

The correlation factor for mixed nearest and next-nearest neighbour monovacancy jumps is calculated as a function of the jump frequency ratio. The diffusion is discussed in terms of a one-defect and several two-defect models. A pronounced temperature dependence of the diffusion energy as well as a marked divacancy contribution at high temperatures can be excluded for the refractory metals. While the measured temperature functions of the isotope effect are compatible with mixed nearest and next-nearest neighbour jumps, there is no proof for the existence of self-interstitial contributions to the diffusion. (author)