Atomic dynamics of icosahedral Al₆₂Cu_25.5Fe_12.5 and tetragonal Al₇₀Cu₂₀Fe₁₀: A comparative study using inelastic neutron scattering

The total dynamic structure factor S(Q, ω) and the generalized vibrational density of states G(ω) have been determined for icosahedral Al₆₂Cu_25.5Fe_12.5 and, for comparison, for tetragonal Al₇₀Cu₂₀Fe₁₀ using inelastic cold neutron scattering. The strongly structured spectra expected on theoretical grounds for the icosahedral alloy were not found in this investigation with a sample at this best concentration known so far for icosahedral AlCuFe. Instead, we found a broad intensity distribution in S(Q, ω) and a broad two-band structure in G(ω) for the icosahedral alloy, not very different from what one would expect for a disordered solid. In contrast, the dynamic structure factor and the phonon density of states of tetragonal AlCuFe measured under identical experimental conditions are very sharply structured in the whole energy region covered in this experiment.