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

Abstract

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.

Thermoelectric Properties of Co-Substituted Al–Pd–Re Icosahedral Quasicrystals

“…The κ phonon,373K was suppressed to 0.94 W m −1 K −1 by Co substitution, which is attributed to decreasing the phonon relaxation time ( τ phonon ): where C v and v s are the specific heat at constant volume and the effective speed of sound, respectively. Here, the C V [ 35 ] and v s can be expressed as: where V and α are the atomic volume and the linear thermal expansion coefficient, respectively. Although we have no information on α for the present i -Al–Pd–Re–Co QCs, qualitative changes are discussed using C P .…”

Atomic diffusion due to hyperatomic fluctuation for quasicrystals

“…In particular, several quasicrystals at high temperatures show significant increases in heat capacity. The heat capacity per atom at a constant volume c V for icosahedral Al-Pd-Mn [9][10][11], Al-Cu-Fe [12], Al-Cu-Ru [13], and decagonal Al-Cu-Co [9,10] QCs show large upward deviations from the Dulong-Petit limit 3k B , where k B is the Boltzmann constant. Such anomalous heat capacity at high temperatures has been debated for over two decades, and a potential connection to the hidden higher-dimensional properties of QCs has been discussed.…”

“…The phason, which contains additional degrees of freedom because of the hyperlattice structure [14,15], has been suggested as the origin of the high-temperature anomalous heat capacity [11,16]. The phason modes originate from the fact that the free energy of the system is invariant under a rigid translation of the parallel space in the perpendicular dimension, where the hyperlattice decomposes into the parallel (physical) and the perpendicular space.…”

“…As the degree of approximation increases, the AC becomes closer in structure to the QC. The AC-specific heat is expected to become more anomalous as it approaches the QC limit because the phason degrees of freedom may increase [11,13].…”

Reduction of Thermal Conductivity for Icosahedral Al-Cu-Fe Quasicrystal through Heavy Element Substitution

“…Here, we selected Au and Pt as substitution elements for Cu because of the large atomic radii, strong bond strength with Al, and a high melting point of Pt. From the experimental point of view, investigating high-temperature thermal conductivity is of great importance for controlling the unusual increase in the specific heat [15][16][17][18][19] for Al-based QCs and approximants, which provides an additional route to tune the thermoelectric [3] and thermal rectifier [12] properties.…”