Self-Diffusion in IcosahedralAl72.4Pd20.5Mn7.1and Phason Percolation at

Abstract

Aluminum self-diffusion in a monodomain icosahedral quasicrystal Al 72.4 Pd 20.5 Mn 7.1 has been studied at temperatures between 4 and 400 K by 27 Al NMR measurements of the decay of transverse nuclear spin magnetization in a spatially inhomogeneous electric field gradient. Temperature dependence of the renormalized diffusion constant can be explained in the framework of the Kalugin-Katz phason-assisted diffusion model where the atomic jumps occur as a result of the presence of matching-rules violation defects. The observed self-diffusion process resembles a percolation transition with the percolation threshold at 72 K. [S0031-9007 (98)08203-9] PACS numbers: 61.44.Br, 76.60. -k

NMR methods for detection of slow atomic motions in quasicrystals

“…Ultrasound experiments analyze the observed motion at very low temperatures in terms of tunneling states. NMR experiments have observed slow, diffusive, lowactivation-energy atomic motions at low temperatures (from 400 to 4 K) in icosahedral i-AlPdMn [14] and decagonal d-AlNiCo [15] and at very low temperatures (down to 100 mK) in i-AlPdRe [16]. At present there is no clear experimental link between the high-temperature thermally activated processes (as observed by radiotracer diffusion and neutron experiments) and the lowtemperature processes observed by ultrasound and NMR.…”

“…In all of the above experiments, the jump processes were thermally activated and the extrapolation of their frequencies to low temperatures (such as room temperature or below) indicates that these processes should there be static, frozen on any accessible experimental time scale. In the low-temperature regime, on the other hand, ultrasound [11][12][13] and NMR [14][15][16] experiments reported atomic motions in QCs that persist down to very low temperatures, indicating the presence of low-activation-energy atomic transfer processes. Ultrasound experiments analyze the observed motion at very low temperatures in terms of tunneling states.…”

In situ high-resolution transmission electron microscopy observation of the phason-strain relaxation process in an Al-Cu-Co-Si decagonal quasicrystal

“…3 Quenched phason strains are often observed experimentally as shifts and broadenings of diffraction peaks [7][8][9] which correlate with the phason momentum G Ќ , and as jogs in atomic rows in high-resolution transmission electron microscopy (HRTEM) images 7-10 and in scanning tunneling microscopy (STM) images. 11 On the other hand, dynamical phasons or thermally-induced phason flips have been investigated by neutron scattering, [12][13][14] by Moessbauer spectroscopy, 15 by NMR, 16,17 and by heat capacity measurements. 18,19 Long wavelength phason fluctuations have been investigated by x-ray and neutron diffuse scattering measurements.…”

Thermal phason fluctuation in an Al–Cu–Co decagonal quasicrystal

“…, and as jogs in atomic rows in high-resolution transmission electron microscopy (HRTEM) images [4,7] and in scanning tunneling microscopy (STM) images [8]. On the other hand, dynamical phasons, or thermally-induced phason flips, have been investigated by neutron scattering [9][10][11][12], by M€ ossbauer spectroscopy [13], by NMR [14,15] and by heat capacity measurements [16,17]. Long wavelength phason fluctuations have been investigated by X-ray and neutron diffuse scattering measurements [18][19][20].…”