High temperature specific heat of Al-Pd-Mn and Al-Cu-Co quasicrystals

For the purpose of investigating the behavior of thermally excited phasons, specific heat has been measured by differencial scanning calorimetry (DSC) for icosahedral Al-Pd-Mn (i-Al-Pd-Mn) in the temperature range from 550 to 1080 K and for decagonal Al-Cu-Co (d-Al-Cu-Co) in the range from 890 to 10 70 K. The measured specific heat per atom at constant pressure c(p) has bee n converted to that at constant volume c(v) by use of the data of bulk modu lus previously reported and the data of thermal expansion coefficient which we measured by X-ray diffractometry. c(v) of i-Al-Pd-Mn is about three k(B ) up to about 700 K, as expected from the Dulong-Petit's law. However, it s tarts deviating upward from three k(B) at about 700 K, increases dramatical ly and reaches five k(B) at 1080 K. The Similar behavior has been observed also for d-Al-Cu-Co. The origin of such a dramatic increase in c(v) is disc ussed in light of possible thermal excitation of phasons. (C) 2000 Elsevier Science B.V. All rights reserved.