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 10SO K for an icosahedral quasicrystal of Al-Pd-Mn, a decagonal quasicrystal of AI-Cu-Co and a crystal approximant of Al-Pd-Fe. The measured specific heat per atom at constant pressure c(p)(T) has been converted to that at constant Volume c(v)(T) by use of the data of bulk modulus previously reported and the data of the thermal expansion coefficient which we measured by dilatometry. c(v)(T) of all three samples stay at around 3k(B) up to about 700 K, as expected from Dulong-Petit's law. For the two quasicrystals, however, c(v)(T) increases dramatically and reaches 4.7k(B) at 1080 K. In contrast, the deviation in c(v)(T) of the crystal approximant is small; it is about 3.6k(B) at 1080 K. The origin of the large deviations in c(v)(T) of the quasicyrstals from Dulong-Petit's value is discussed in light of thermal excitation of phasons. (C) 2001 Elsevier Science B.V. All rights reserved.