THE INFLUENCE OF SCANDIUM ON THE ANOMALOUS SELF-DIFFUSION IN BCC-ZIRCONIUM

The temperature dependence of **9**5Zr diffusion and the isotope effect of **8**8Zr and **9**5Zr were measured in alloys with 6. 7 and 13. 6 at. % scandium. The Arrhenius plots are more strongly curved than those for self-diffusion in pure beta -Zr, the opposite to previous findings in Zr-Nb alloys. The results of the isotope effect are consistent with a predominant monovacancy mechanism. The diffusion anomaly is explained by phonon assisted diffusion jumps. Values of the frequency factor and the activation enthalpy representing normal diffusion behaviour are calculated. A systematic variation in the electronic structure when alloying Vb and IIIb metals, respectively, to IVb metals is responsible for the continuous change in the diffusion anomaly of beta -Zr-Nb alloys, pure beta -Zr and beta -Zr-Sc alloys.