Effect of hydrostatic pressure and temperature on the self-diffusion rate in single crystals of silver and gold

Abstract

The pressure dependence of the rate of self-diffusion has been measured up to about 6 kbar by a radiotracer sputter-sectioning technique in Ag at 594, 683, 766, 885 and 994 K and in Au at 692 K. In the case of Aga gradual increase of the activation volume from 0.66ω (ω=atomic volume) to 0.84ω was observed. This observation may be considered as a further ‘weak’ anomaly of self-diffusion in addition to the already known curvature of the Arrhenius plot at ambient pressure and the decrease of the isotope effect with increasing temperature. In the case of Au the activation volume of 0.73ω from the present work, together with literature values near the melting temperature, indicates that the activation volume is almost temperature independent. This observation fits into the overall picture that for Au the other two anomalies are also very weak.

It is concluded that a consistent analysis of the available data is possible in terms of the monovacancy-divacancy model. It appears that an interpretation of self-diffusion in terms of monovacancies with strongly temperature-dependent activation enthalpies, entropies and volumes alone, is not consistent with the available data.