Density functional (DFT) theory and semiclassical Boltzmann theory are used to calculate structural, mechanical, electronic, and transport properties of RuVAs and RuNbAs half‐Heusler alloys. The band structure calculations reveal a p‐type semiconducting state with narrow indirect (L–X) gap values of 0.20 and 0.36 eV for RuVAs and RuNbAs alloys, respectively. The Seebeck coefficient S, electrical conductivity σ, thermal conductivity κe, and figure of merit ZT are calculated in the temperature range 100–1200 K. The lattice thermal conductivity κL and the relaxation time τ are also determined. At room temperature, RuVAs and RuNbAs alloys exhibit ZT values of 0.22 and 0.30 respectively, which correspond to the lattice thermal conductivity κL equal to 18.67 and 15.14 W m−1 K. κL rapidly decreases with increasing temperature. In addition, the maximum value of ZT reaches 0.47 at 900 K and 0.62 at 1000 K for RuVAs and RuNbAs alloys, respectively. Consequently, these compounds could be a candidate for use as p‐type thermoelectric materials operating at high temperatures.

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