SELF-DIFFUSION AND LATTICE-DYNAMICS IN A BCC TL-IN SOLID-SOLUTION

A combined study of tracer diffusion of Tl-204 and inelastic neutron s cattering in a b.c.c. Tl-In (17 at%) solid solution is presented. In c ontrast to self-diffusion behaviour in b.c.c. alkali and transition me tals, which is characterized by a certain systematics and non-linear A rrhenius relations, the classification of self-diffusion for the only main group b.c.c. metal beta-Tl in terms of normal or ''anomalous'' is still unclear because the small temperature range of existence of its b.c.c. phase does not allow decisive experiments. Alloying the homolo gous element In to Tl extends this range drastically and improves the possibility to study both the temperature dependence of self-diffusion and of the phonon dispersion. On the basis of the phonon measurements vacancy migration enthalpies are calculated, being independent of tem perature. This result is conform with the measured perfectly straight Arrhenius plot of self-diffusion in b.c.c. Tl-In (17 at%). Our combine d investigations provide arguments for classifying self-diffusion of b eta-Tl - opposite to the diffusion behaviour of b.c.c. transition meta ls - as normal.