Thermoelectric properties of Tsai-type Au–(Al, Ga, In)–Gd approximants

Abstract

In this work, the thermoelectric properties of Tsai-type Au–(Al, Ga, In)–Gd approximant crystals (ACs) are investigated over a temperature range of 300–773 K. The changes in lattice constants and effective speed of sound suggest a weaker chemical bonding caused by a replacement of Al by heavier Ga or In atoms. Based on electrical conductivity measurements, Au–Al–Gd shows the deepest pseudogap in spectrum conductivity at the Fermi level, followed by Au–Ga–Gd and Au–In–Gd ACs. The lattice thermal conductivity at 300 K is as low as 0.71–0.81 W m−1 K−1 and asymptotically approaches a minimum lattice thermal conductivity of 0.52–0.59 W m−1 K−1 as calculated using the Cahill model. As a result, the highest power factor and dimensionless figure of merit reach ∼120 µW m−1 K−2 and ∼0.008 at ∼700 K for the Au–In–Gd system. Our systematic approach of weakening the chemical bonding nature by heavy atom substitution promises a better thermoelectric performance of Tsai-type ACs.