Reinvestigation of the thermoelectric properties of Fe-substituted icosahedral Al-Pd-Re quasicrystals

Icosahedral quasicrystals (QCs) have a glass-like, low thermal conductivity because of their complex crystal structures, and a moderate power factor because of deep pseudogap formation in their electronic density of states (DOS) at the Fermi level originating from icosahedral symmetry and covalent bonding nature. These features are beneficial for high-performance thermoelectric materials. Densified bulk samples of icosahedral Al-Pd-Re-Fe QCs are synthesized by arc-melting, annealing, and spark plasma sintering methods. It is found that a 2/1-approximant crystal (AC) can be produced by higher Fe substitution [Al${}_{71}$Pd${}_{20}$(Re${}_{1-x}$Fe${}_x$)${}_9$ (x ≥ 0.75)]. The thermoelectric properties of Al${}_{71}$Pd${}_{20}$(Re${}_{1-x}$Fe${}_x$)${}_9$ (where x = 0, 0.2, 0.4, 0.65, 0.7, and 0.75) are evaluated between 373 and 973 K. Fe substitution enhances the power factor and reduces the phonon thermal conductivity by a concept of "weakly bonded rigid heavy clusters" (WBRHCs) and an increase in the carrier concentration, enhancing the dimensionless figure of merit (zT). The 2/1-AC phase has a much higher electrical conductivity and a moderate Seebeck coefficient in the mid-temperature region due to a considerable increase in carrier concentration; this results in the highest power factor of 900 µW m${}^{-1}$ K${}^{-2}$, and zT value for the 2/1-Al-Pd-Re-Fe AC is 0.26 at 573 K. (© 2022 Wiley‐VCH GmbH)