First Low-Temperature Radiotracer Studies of Diffusion in Icosahedral Quasicrystals

The diffusivities of implanted, radioactive ${}^{103}\mathrm{Pd}$ and ${}^{195}\mathrm{Au}$ in icosahedral ${\mathrm{Al}}_{70.4}{\mathrm{Pd}}_{20.8}{\mathrm{Mn}}_{8.8}$ quasicrystals were measured between 810 and $270°\mathrm{C}$ by a radiotracer technique, where serial sectioning was done by high-precision grinding or ion-beam sputtering. Both diffusion coefficients obey different Arrhenius laws above and below $450°\mathrm{C}$. Whereas diffusion above this temperature is explained in terms of a vacancy mechanism that reflects the heterogeneity of the icosahedral structure, diffusion below $450°\mathrm{C}$ is proposed to occur via a phason-assisted direct mechanism.