Optic modes in the AlPdMn icosahedral phase

Abstract

The dynamics of the icosahedral phase AlPdMn have, been reinvestigated on a centimetre-size single grain using inelastic neutron scattering measurements. As previously found, well defined acoustic modes are observed close to seong Bragg reflections. Transverse acoustic phonons remain resolution limited for wavevectors smaller than 0.35 A-' and a bmadening occurs for larger wavevectors. Beside acoustic modes, the ,scattering function S(Q, o) shows an extremely rich shucture. A series of bmad (1 THz) dispersionless excitations appears with energies close Io 1% 3, 4 and 5.5 THr These excik2tions were found at different points in r e c i p r d space and present intensity variation. Some of these 'optic' bands miglv be associated with crossings at quasiBrillouin zone boundaries. The system has also been investigated at high temperamm up to 80OOC. Beyond a 10% reduction of the sound velocity. results are identical to those obtained at nwm temperarure. In particular the lransverse acoustic modes remain resolution limited for wavevectors smaller than 0.35 A-'.

Electrical, magnetic, thermal and thermoelectric properties of the “Bergman phase” Mg32(Al,Zn)49 complex metallic alloy

“…The hopping contribution κ H becomes significant above 70 K and the hopping activation energy was found to be E a = 15.7 meV. This E a value is very similar to that found in the ␤-Al 3 Mg 2 CMA compound [21] (where E a = 16.9 meV for the monocrystalline sample), as well as to those determined by inelastic neutron (INS) [41][42][43] and X-ray [44] scattering experiments in Al-based QCs, such as the i-Al-Pd-Mn and iAl-Cu-Fe families, where dispersionless vibrational states were identified for energies higher than 12 meV. In QCs, such dispersionless states indicate localized vibrations and are considered to be a consequence of a dense distribution of energy gaps in the phonon excitation spectrum.…”

Complex ɛ-phases in the Al–Pd-transition–metal systems: Towards a combination of an electrical conductor with a thermal insulator

“…The average hopping activation energy of the localized vibrations is E a = 209 ± 49 K (or 18 ± 4 meV), which is similar to the values observed in i-Al-Pd-Mn QCs (that are structurally based on the same Mackay-type icosahedral cluster) by the inelastic neutron-(INS) [34][35][36] and X-ray [37] scattering experiments. The average values of the exponents α and β that govern the frequencyand temperature dependence of the umklapp rate (recall that τ −1 um ∝ ω α T β−α ) areᾱ = 2.0 ± 0.4 andβ = 3.8 ± 0.8, yielding the average dependence τ −1 um ∝ ω 2 T 1.8 .…”

Magnetic, electrical and thermal transport properties of Al–Cr–Fe approximant phases

“…On both graphs, the individual contributions κ el (T), κ D (T) and κ H (T) to the total κ(T) are also displayed. Due to the very small temperature dependence of ρ(T) that enters the Wiedemann-Franz law, the electronic contribution κ el (T) exhibits practically linear temperature dependence and the correction factor ε was found to be either small (amounting 0.14 for the O 1 /O 2 -AlCrFe) or negligible (−2 × 10 −3 for [27][28][29] and X-ray [30] scattering experiments on i-Al-Pd-Mn QCs, where dispersionless vibrational states were identified for energies higher than 12 meV. Such dispersionless states are considered to be a consequence of a dense distribution of energy gaps in the phonon excitation spectrum, which prevents extended phonons from propagating through the lattice, whereas localized vibrations may still be excited.…”