The pressure dependence of self-diffusion in the high-temperature body-centered cubic phase of Zr was studied by using radio-tracer techniques. Activation volumes of 0.184O at 1423K and 0.213O at 1273K were obtained, where O was the atomic volume. The activation volumes for 95Nb diffusion were equal to 0.161 O at 1423K and 0.193 O at 1273K. The small activation volumes indicated a large relaxation of the vacancy. This in turn reflected the inherent weakness, of the body-centered cubic lattice, with regard to shear in the <111> direction. These results (tables 21 and 22) provided an explanation for the absence of positron trapping in group-IV transition metals.

Pressure Dependence of Self- and Solute-Diffusion in BCC Zirconium P.Knorr, J.Jun, W.Lojkowski, C.Herzig: Physical Review B, 1998, 57[1], 334-40

Table 21

Diffusivity of 95Zr in ß-Zirconium

Table 22

Diffusivity of 95Nb in ß-Zirconium