Dynamics in the melt of an icosahedral Al₇₂Pd ₂₀Mn₈ quasicrystal

The dynamic structure factor S(Q,ω) of the melt of an icosahedral quasicrystal, Al₇₂Pd₂₀Mn₈, was measured at 1223K near the melting point, T_m ≤ 1140K, for momentum transfers, Q, from 1.5 to 27.15nm^-1 by means of an inelastic x-ray scattering technique using synchrotron radiation at SPring-8. The composition of Al ₇₂Pd₂₀Mn₈ is a special one in AlPdMn ternary alloys, since an icosahedral AlPdMn quasicrystal is formed from the melt. The acoustic mode was observed in the low-Q region, and a substantial broadening of the longitudinal current-current correlation function and the crossover of the effective sound velocity from hydrodynamic to viscoelastic regions were observed around 6nm^-1, which hints at the existence of a cluster with a size of about 1nm in the melt.