${}^{27}\mathrm{Al}$ NMR measurements of the transverse magnetization decay in a decagonal quasicrystal ${\mathrm{Al}}_{72.6}{\mathrm{Ni}}_{10.5}{\mathrm{Co}}_{16.9}$ detected at temperatures between 300 and 4 K slow, low-activation-energy, diffusive atomic jumps that exhibit properties compatible with the elementary excitations of the quasiperiodic lattices in the form of phason jumps. However, identical atomic motion was observed also in “vacancy-ordered” bcc crystalline ${\mathrm{Al}}_{50}{\mathrm{Cu}}_{35}{\mathrm{Ni}}_{15},$ indicating that this motion is not quasicrystals specific, but a feature of close-packed atomic structures—either periodic or quasiperiodic—that contain structural vacancies.

• Received 10 April 2002

DOI:https://doi.org/10.1103/PhysRevB.65.212203