Ab-initio investigation on the electronic and thermoelectric properties of new half-Heusler compounds KBiX (X = Ba and Sr)

Electronic structures and thermoelectric (TE) properties of KBiBa and KBiSr half-Heusler compounds are investigated by using the combined framework of first-principles and semi-classical Boltzmann transport theory. Elastic and phonon properties calculations reveal that these compounds are mechanically and dynamically stable. Band structures calculations, using the Tran and Blaha modified Becke–Johnson potential including spin–orbit coupling, show that KBiBa and KBiSr compounds are semiconductors with an indirect bandgap of 0.88 and 0.95 eV respectively. Performing calculations on lattice thermal conductivity, deformation potential, effective mass of charge carriers and their relaxation times allow us to deduce the dependence of the figure of merit ZT on doping concentration and temperature. At 1200 K, KBiBa and KBiSr compounds exhibit a ZT peak value of 2.68 and 1.56 at optimized n-doping values of 2.2 × 10¹⁹ and 1.7 × 10¹⁹ cm⁻³, respectively. Considering high ZT values, KBiBa and KBiSr are considered to be ideal TE candidates at high temperature. (paper)