Comparative study of high-temperature specific heat for Al–Pd–Mn icosahedral quasicrystals and crystal approximants

Quasicrystals (QCs) have a peculiar structural order characterized by quasiperiodicity and non-crystallographical point group symmetry. To reveal their characteristic physical property reflecting the peculiar structural order, specific heat measurements were performed for Al–Pd–Mn icosahedral QCs (i-QCs) and a series of crystal approximants (CAs) of 2/1- 1/1- and 1/0-cubic types at 400–1200 K. The measured specific heat per atom at constant pressure c P was converted to that at constant volume c V by using data of the thermal expansion coefficient and bulk modulus. Below ∼700 K, the c V values of all the specimens of i-QCs and CAs were close to 3 k B ( k B : Boltzman’s constant), i.e., they obeyed Dulong–Petit’s law. With further increase in temperature, the i-QCs showed a dramatic increase in c V with increasing temperature, and reached 5 k B at 1100 K. In contrast, the 2/1 CAs showed a similar but slightly smaller increase in c V , whereas the 1/1 and 1/0 CAs showed a negligible increase. The systematic behavior of c V in the order of CAs and QC demonstrates that a large excessive specific heat is a characteristic feature of QCs, reflecting the peculiarity of their structural order. Its possible physical mechanism was discussed in terms of anharmonic atomic vibrations, electronic excitations, and phasonic excitations.