Reversible and irreversible changes in the thermal conductivity of amorphous PdCuSi

We report on measurements of the thermal conductivity at low temperatures on amorphous Pd_77.5Cu₆Si_16.5 after different annealing steps. The phonon thermal conductivity ^ph increases systematically after irreversible annealing. The change of ^ph is strongly correlated with an equivalent change in the amount of free volume in the amorphous structures. The present results support the validity of the free volume model developed to explain the existence of low-energy excitations in amorphous metals. In contrast to the irreversible changes in ^ph, also reversible changes occur which are attributed to effects in chemical short range ordering in the metallic glass PdCuSi.