We report the thermoelectric properties of polygrain icosahedral Al 71Pd 20Mn 9 and Al 71Pd 20Re 9 quasicrystals (QCs). The microstructure of polygrain (arc-melted and annealed) Al-Pd-Re QCs is highly porous. We synthesized sintered pellets of the Al 71Pd 20Re 9 QC by the spark plasma sintering (SPS) method, resulting in an improvement in their relative density from 65% to more than 99%. This enables direct comparison of Al 71Pd 20Mn 9 QCs with Al 71Pd 20Re 9 QCs. The maximum dimensionless figures of merit ZT were 0.18 and 0.12 for Al 71Pd 20Mn 9 and Al 71Pd 20Re 9 QCs, respectively. For further improvement of the ZT value, we substituted Ga for Al atoms in the Al 71Pd 20Mn 9 QC in accordance with the guiding principle of weakly bonded rigid heavy clusters (WBRHCs). The sound velocity and Debye temperature beneficially decreased with increasing Ga concentration, indicating weakening of the intercluster bond strength, as predicted for WBRHCs. The maximum ZT value was increased by a factor of 1.4 from 0.18 for the Al 71Pd 20Mn 9 QC to 0.26 for the Al 68Ga 3Pd 20Mn 9 QC by the addition of an alloying effect to that of the WBRHCs.
ASJC Scopus subject areas