Effects of Cu doping on thermoelectric properties of Al–Si–Ru semiconducting quasicrystalline approximant

Abstract

We have attempted to improve the thermoelectric performance of an Al--Si--Ru semiconducting approximant through optimizing the carrier concentration. The effects of Cu doping on the thermoelectric properties of an Al--Si--Ru semiconducting quasicrystalline approximant with the nominal composition of ${\mathrm{Al}}_{69\ensuremath{-}0.75x}{\mathrm{Si}}_{7.5}{\mathrm{Cu}}_{x}{\mathrm{Ru}}_{23.5\ensuremath{-}0.25x}\phantom{\rule{4pt}{0ex}}(x=0,2,4,6,8)$ are investigated. At approximately room temperature, an increase of $x$ leads to a decrease of the Seebeck coefficient $S$ and an increase of the electrical conductivity. Density functional theory and the Boltzmann transport theory are used to calculate $S$ as the hole concentration and the band gap are varied. The temperature dependence of $S$ is quantitatively described by an increase of the hole concentration and narrowing of the band gap with increasing $x$. Cu doping is shown to increase the hole concentration and narrow the band gap. The maximum dimensionless figure of merit increases from 0.03 at 400 K for $x=0$ to 0.2 at 500 K for $x=4$. These results indicate that the semiconducting quasicrystalline approximant could be a suitable candidate as a thermoelectric material for low grade waste heat recovery.