New phase of lead chalcogenide alloy: Ternary alloy PbSrSe₂ for future thermoelectric application

Lead chalcogenides PbX (X = S, Se, Te) have gained widespread research interest due to their excellent thermoelectric properties. In contrast, their ternary structures, which are projected to exhibit enhanced thermoelectric performance, have not been fully explored. In this work, variable composition search of stable Pb–Sr–Se compounds has been performed by means of evolutionary algorithm combined with first principles calculations. A new tetragonal phase, PbSrSe₂, is found and its structural stability has been verified through phonon dispersion and elasticity calculations. Along the way, we investigated the mechanical properties such as elastic moduli, Poisson's ratio, Vickers's hardness and fracture toughness. PbSrSe₂ shows lower lattice thermal conductivity than its parent structures (PbSe and SrSe) which is 0.25 W/mK. At optimum hole doping concentration of 10¹⁹ cm⁻³, its predicted figure of merit reaches 0.9 at 1000 K.