Transport properties of RuV-based half-Heusler semiconductors for thermoelectric applications: a computational study

A systematic study of electronic structure, mechanical and transport properties of RuV-based half-Heusler alloys (RuVZ, Z = As, P, Sb) have been presented using ab initio density functional and Boltzmann transport theory. The electronic structures are obtained using generalized gradient approximation with Perdew-Burke-Ernzerhof functional. All the compounds are crystallized in face centered cubic phase with space group #216. Our preliminary electronic structure simulations reveal that all the alloys are non-magnetic semiconductors. Additionally, the phonon dispersion and elastic constants (along with the related elastic moduli) also verify mechanical stability of the alloys. Due to strong dependence on the electronic bandgap in thermoelectric materials, we have estimated bandgap using more accurate hybrid functional i.e. Heyd-Scuseria-Ernzerhof. The transport coefficients (e.g. Seebeck, electrical conductivity, thermal conductivity due to electrons) are calculated by solving the Boltzmann transport equation for charge carriers as implemented in BoltzTraP software under constant relaxation time approximation. The lattice thermal conductivity due to phonons is calculated using more reliable shengBTE code based upon the Boltzmann transport equation for phonons. We have calculated the more reliable value of the thermoelectric figure of merit, ZT (related to the conversion efficiency) for all the compounds. The obtained ZT for RuVAs, RuVP and RuVSb is 0.41(0.32), 0.21(0.16) and 0.70(0.61) for p(n)-type behavior at 900 K. The corresponding carrier concentrations are also predicted. High value of ZT is obtained for RuVSb alloy due to low lattice thermal conductivity. Among these compounds, RuVSb emerged out as a most suitable candidate for thermoelectric power generation device. Minimum lattice thermal conductivity in theoretical limit along with the corresponding maximum value of ZT is also predicted in these alloys.