High-temperature thermoelectric properties of half-Heusler phases Er$_{1-x}$Ho$_x$NiSb

TL;DR

This study investigates the high-temperature thermoelectric properties of Er$_{1-x}$Ho$_x$NiSb half-Heusler alloys, revealing optimal compositions with enhanced power factors suitable for thermoelectric applications.

Contribution

It provides new insights into how Ho substitution affects thermoelectric performance in ErNiSb-based half-Heusler phases, identifying compositions with improved power factors.

Findings

Maximum thermopower of 50-65 μV/K at 500-650 K

Largest power factor of 4.6 μWcm$^{-1}$K$^{-2}$ at 660 K for x=0.5

Non-monotonous variation of thermoelectric power factor with Ho content

Abstract

Polycrystalline samples of Er$_{1-x}$Ho$_x$NiSb ($x$ = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and optical metallography. The results proved the formation of half-Heusler alloys in the entire composition range. Their electrical transport properties (resistivity, thermoelectric power) were studied in the temperature interval 350-1000 K. The measured electrical resistivity spanned between 5 and 25 $\mu \Omega$m. The maximum thermopower of 50-65 $\mu$V/K was observed at temperatures 500-650 K. Replacing Ho for Er resulted in a non-monotonous variation of the thermoelectric power factor ($PF = S^2/\rho$). The largest $PF$ of 4.6 $\mu$WcmK$^{-2}$ was found at 660 K for Er$_{0.5}$Ho$_{0.5}$NiSb. This value is distinctly larger than PF determined for the terminal phases ErNiSb and HoNiSb.