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 1070 K. The measured specific heat per atom at constant pressure cp has been converted to that at constant volume cv by use of the data of bulk modulus previously reported and the data of thermal expansion coefficient which we measured by X-ray diffractometry. cv of i-Al–Pd–Mn is about three kB up to about 700 K, as expected from the Dulong–Petit’s law. However, it starts deviating upward from three kB at about 700 K, increases dramatically and reaches five kB at 1080 K. The Similar behavior has been observed also for d-Al–Cu–Co. The origin of such a dramatic increase in cv is discussed in light of possible thermal excitation of phasons.