Diffusion in quasicrystalline Al-Ni-Co and Al-Pd-Mn

Diffusion coefficients of ⁶⁰Co in single decagonal (d-)Al_72.2Ni_11.8Co_16.0 quasicrystals and of ⁶³Ni in single icosahedral (i-)Al₇₀Pd₂₁Mn₉ were measured by the radioactive tracer method. The volume diffusion coefficients can be described by an Arrhenius equation. Anisotropic diffusion behaviour was observed in the d-Al-Ni-Co quasicrystals, in which the mobility of Co is slightly faster along the periodic direction. The activation enthalpies for Co diffusion in d-Al-Ni-Co are Q = 277.4 kJ mol^-1 (periodic direction), Q = 289.0 kJ mol^-1 (aperiodic direction) and for Ni diffusion in i-Al-Pd-Mn Q = 209.0 kJ mol^-1. The results are discussed together with data of similar diffusion investigations in icosahedral quasicrystals, and a diffusion mechanism via vacancies is suggested. In addition, we have determined surface self-diffusion coefficients of ⁶⁰Co in the d-Al-Ni-Co quasicrystalline alloy and have obtained different activation energies of surface diffusion for the periodic (Q = 147 kJ mol^-1) and the quasiperiodic direction (Q = 137 kJ mol^-1).