High-temperature specific heat of quasicrystals and a crystal approximant

Specific heat measurements have been performed by DSC in the temperature range from 430 to 1080 K for an icosahedral quasicrystal of Al–Pd–Mn, a decagonal quasicrystal of Al–Cu–Co and a crystal approximant of Al–Pd–Fe. The measured specific heat per atom at constant pressure cp(T) has been converted to that at constant volume cv(T) by use of the data of bulk modulus previously reported and the data of the thermal expansion coefficient which we measured by dilatometry. cv(T) of all three samples stay at around 3kB up to about 700 K, as expected from Dulong–Petitʹs law. For the two quasicrystals, however, cv(T) increases dramatically and reaches 4.7kB at 1080 K. In contrast, the deviation in cv(T) of the crystal approximant is small; it is about 3.6kB at 1080 K. The origin of the large deviations in cv(T) of the quasicyrstals from Dulong–Petitʹs value is discussed in light of thermal excitation of phasons.