Thermoelectric properties of semiconducting approximant crystals in the Al–Ge–Ru system

Semiconducting quasicrystals and their approximant crystals (ACs) have attracted significant attention because of their potential applications as thermoelectric materials. Herein, we report the synthesis of a semiconducting AC in the Al–Ge–Ru system and its thermoelectric properties. The Al–Ge–Ru AC exhibited a band gap of approximately 0.25 eV. Notably, we observed a negative Seebeck coefficient, which reached a maximum magnitude of 200 µV K −1 , marking the first example of an n-type semiconducting AC. The Al 74 Ge 4 Ru 22 AC exhibiting degenerate semiconductor behavior reached a dimensionless figure of merit of 0.28 at a peak temperature of 473 K. This represents the highest figure of merit achieved to date for a quasicrystalline-based thermoelectric material.