First-Principles Insights Into Thermoelectric Performance of Pb-Free Halide-Based Ba3PX3 (X = Cl, Br) Compounds

Abstract

We present a density functional theory-based study of the thermoelectric properties of Ba₃PX₃ (X = Cl, Br) compounds. Both compounds are dynamically stable and exhibit direct band gap semiconducting behaviour evident from electronic structure calculations. The antibonding states resulting from anion–cation hybridization reduce the phonon stiffness and enhances phonon scattering, resulting in low lattice thermal conductivity in these compounds. The lattice thermal conductivity values are reported as low as 0.25 W/mK at 800 K for Ba₃PCl₃. Electronic structure plots reveal that the high band degeneracy near the band edges enhances carrier conduction channels without degrading the Seebeck coefficient, a desirable feature in high-performance thermoelectric materials. These effects contribute to a ZT value of 1.13 for n-type Ba₃PCl₃ at 800 K temperature. The results establish Ba₃PX₃ as a promising class of Pb-free thermoelectric materials with performance driven by intrinsic phonon scattering mechanisms.