Enhanced thermoelectric performance of Ru2TiSi Heusler compounds with Ta substitution

Abstract

The Ru2TiSi Heusler compound can be classified as a semimetal, with a deep pseudogap near the Fermi level, because of the possession of a valence electron concentration VEC of 6.0. In this study, we investigate the electrical and thermal transport properties of Ru2Ti1-xTaxSi (x = 0 – 0.20) compounds and evaluate their thermoelectric performance up to a temperature of 1000 K. The pristine Ru2TiSi compound displays a p-type Seebeck coefficient (S) that peaks at S = 185 μV/K around 700 K. Notably, the power factor for Ru2TiSi gradually increases with temperature and reaches a value of 4.4 × 10–3 W/mK2 at 830 K. Upon partial substitution of Ta, a significant change occurs, resulting in n-type thermoelectric conduction with a Seebeck coefficient of S = –155 μV/K at 680 K for x = 0.03. The thermal conductivity (κ) of Ru2TiSi is approximately 20 W/mK at 300 K, but the substitution of Ta dramatically reduces κ to 4.5 W/mK for x = 0.20, which remains almost unchanged with temperature. Through thermoelectric measurements on the sintered alloys, we determined the dimensionless figure of merit, ZT, to be 0.42 for p-type Ru2TiSi at 1000 K and 0.42 for n-type Ru2Ti0.80Ta0.20Si at 900 K, both of which are some of the highest values ever achieved for bulk thermoelectric Heusler compounds.