Pressure dependence of self- and solute diffusion in bcc zirconium

Abstract

The pressure effect of self-diffusion in the high-temperature bcc phase of zirconium has been studied with high accuracy using the radiotracer technique. Activation volumes of $0.184\ifmmode\pm\else\textpm\fi{}0.016\ensuremath{\Omega}$ (\ensuremath{\Omega}: atomic volume) at 1423 K and $0.213\ifmmode\pm\else\textpm\fi{}0.014\ensuremath{\Omega}$ at 1273 K were obtained. Simultaneously, the activation volumes of the ${}^{95}\mathrm{Nb}$ solute diffusion were measured which amount to $0.161\ifmmode\pm\else\textpm\fi{}0.014\ensuremath{\Omega}$ at 1423 K and $0.193\ifmmode\pm\else\textpm\fi{}0.023\ensuremath{\Omega}$ at 1273 K. The small activation volumes indicate a strong relaxation of the vacancy. The large relaxation volume reflects the inherent weakness of the bcc lattice towards a shear in $〈111〉$ direction. The results provide an explanation for the absence of positron trapping in group-IV transition metals.