Role of lattice thermal conductivity in thermoelectric properties of chalcopyrite-type antimonides XSiSb2 (X = Mg, Be): A DFT insight

The widely available low-cost materials with high performance acts as a great choice for thermoelectric energy conversion applications. Here, the thermoelectric properties of two environmentally friendly chalcopyrites namely, MgSiSb2 and BeSiSb2 with tetragonal crystal structure, is investigated systematically. With the help of first principles combined with Boltzmann transport equations and modified Debye-Callaway model, electronic and thermal transport properties are studied. From electronic structures, it is inferred that both the chalcopyrites falls under semiconducting region with narrow band gap. The phonon dispersions suggest that these antimonides are thermodynamically stable with strongly coupled acoustic and optical mode of vibrations. Moreover, MgSiSb2 has high figure of merit (zT) of 2.06 (n = 1 x 1020 cm-3) with ultralow lattice thermal conductivity (kL) of 1.01 W m-1 K-1 at 900 K, whereas, BeSiSb2 has low zT of 0.23 due to its larger kL. Besides, these results demonstrate that this prediction can pave the way for experimental explorations.