A Nuclear Magnetic Resonance Study of Decagonal and Related Crystalline Phases in Al-Cu-Co System

摘要

We have measured ~(27)Al, ~(65)Cu and ~(59)Co spin-echo spectra for Al_(70)Cu_xCo_(30-x)(X=6,l2,l5) Al_(73)Co_(27) and Al_(76.5)Co_(23.5) decagonal quasicrystals and for Al_(76.5)Co_(23.5) monoclinic compound. The line shape and peak shift suggest different local atomic configuration in these phases. It seems that the Al atoms make a quasicrystalline skeleton in the decagonal phase, and the Co atoms also enter symmetric sites three dimensionally. On the other hand, the Cu atoms occupy asymmetric sites characteristic of the decagonal phase. For the Al_(76.5)CO_(23.5) monoclinic compound, the Al atoms occupy the one crystallographic site but the Co atoms occupy three different sites whereas the decagonal phase has a less metallic Co atom among those sites.