Heat capacities of icosahedral and hexagonal phases of Zn–Mg–Y system

Heat capacity measurements have been performed in the temperature range 4–300 K for an icosahedral phase of Zn–Mg–Y alloy (Zn55Mg35Y10) and the related crystalline phases, a hexagonal phase (Zn65.2Mg27.9Y6.9) and the Laves phase of MgZn2, to study the feature of lattice vibrations in quasicrystals. A single quasicrystal of Zn56.8Mg34.6Y8.7 was also investigated for comparison. The vibrational density of states is delineated in terms of the temperature dependence of the apparent Debye temperature (ΘD) on a reduced basis using the limiting value at high temperature (Θ∞). A deeper minimum (ΘD/Θ∞∼0.82) is observed at substantially lower temperatures (T/Θ∞∼0.055) in the quasicrystals than in the crystals, which suggests significant enhancement of the density of states at the corresponding energies. The fact is compatible to that obtained previously for Al–Cu–Ru, Al–Pd–Re and Al–Pd–Mn systems. The presence of some defects or inhomogeneity in quasicrystals might be responsible for the anharmonic lattice vibrations.