Vacancy Control and Enhancement of Thermoelectric Properties of Al–Ir Cubic Quasicrystalline Approximant via High-Pressure Synthesis

Abstract

Although the binary Al–Ir cubic quasicrystalline approximant has been expected to be a narrow-gap semiconductor, it has not yet been produced because the presence of Al site vacancies causes excess hole doping. We suggest that high-pressure synthesis (HPS) can effectively reduce these vacancies. In this work, we investigated how HPS affected the structural and thermoelectric properties of an Al–Ir quasicrystalline approximant, finding that the sample made by HPS had a larger Seebeck coefficient than a sample made by conventional spark plasma sintering (SPS). Further, applying high pressure increased the lattice constant and measured Al composition by increasing the number of Al atoms in the Ir₁₂ icosahedral cluster. These results show that HPS suppressed vacancies in the cluster, which doubled the dimensionless figure of merit zT.

 

This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 16 (2020) 139–143.

Temperature dependence of Seebeck coefficient S for Sample made by spark plasma sintering (SPS) (filled circle), high pressure synthesis (HPS) (square) and the sample of Ref. 10), respectively. Calculated S with 9.5 Al per cluster (solid line) and 9.75 Al per cluster (dashed line) are also shown.