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

Abstract

Although the binary AlIr 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 AlIr 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 Ir 12 icosahedral cluster. These results show that HPS suppressed vacancies in the cluster, which doubled the dimensionless figure of merit zT.