First principle calculations of the structural, elastic, electronic and transport properties of XRuAs (X = Ta and V)

The structural, electronic, elastic, and transport properties of Ruthenium Arsenide based Tantalum and Vanadium (XRuAs (X = Ta and V)) half heusler alloys were investigated as a promising thermoelectric material. In determining the properties of these compounds, density functional theory (DFT), as implemented in Quantum Espresso and Boltztrap codes were used. The alpha atomic position gave the lowest minimum energy and was used for all other calculations. The lattice constants, electronic band structure, total and partial density of state and the elastic properties of the compounds were determined. The electronic band structure calculation showed that TaRuAs and VRuAs were semiconductors with an indirect bandgap of 0.17 eV and 0.42 eV, respectively. The d-orbital of the Ruthenium atom in both compound were responsible for the huge peak observed in the total DOS. The elastic properties showed that the alloys are mechanically stable, ductile and elastically anisotropic. The transport properties calculated are the Seebeck coefficient, power factor, and electronic thermal conductivity. The maximum Seebeck coefficient at 1000 K is 286.30 mu V/K and 212.06 mu V/K, while the maximum electrical conductivity obtained at 1000 K is 4.99 S/ms and 4.11 S/ms. The power factor obtained at 1000 K for VRuAs and TaRuAs were 185.37 W/msK(2) and 166.25 W/msK(2). At 1000 K, an electronic thermal conductivity (TC) of 8.59 W/mK was obtained for TaRuAs, and 8.01 W/mK was obtained for VRuAs. Figures of merit of 0.58 and 0.77 are obtained for VRuAs and TaRuAs, respectively, at 1000 K which is a limit and the final value may be lower with the computation of the lattice thermal conductivity. The Electronic Fitness Functions (EFF) was determined to further screen the compounds. Values of 1.4 W-5/3 ms(1/3) K-2 and 0.77 W-5/3 ms(1/3) K-2 are obtained, which are comparable with the values obtained for high-performance thermoelectric materials. The results showed that while both compounds are good thermoelectric materials, TaRuAs is the better of the two compounds with a higher figure of merit. Moreover, the results obtained from the EFF calculation suggests that the TaRuAs is a good thermoelectric material. As far as we know, the results obtained for TaRuAs have not been presented in any literature.