Atomic-scale structure and thermoelectric properties in medium-entropy PbSnTeSe alloy

Binary IV-VI compounds are typical and promising thermoelectric materials, but their complex solid solutions remain underexplored. Herein, a quaternary PbSnTeSe alloy is screened out from a range of PbSe-SnTe solid solutions through entropy engineering, utilizing its medium entropy to balance phonon and carrier transport properties. Microstructure observation discloses that the medium-entropy PbSnTeSe alloy presents a stable face-centered cubic crystal structure and uniform elemental distribution at the atomic scale, which can cause strong strain and mass fluctuations to effectively suppress lattice thermal conductivity (κ_l). Furthermore, through progressive optimization of electrical transport properties via Sn vacancy and Cu counter doping, an ultra-low lattice thermal conductivity value of 0.29 W m⁻¹ K⁻¹ can be obtained in PbSn_0.98Cu_0.04PbSe at 373 K, and the maximum power factor continuously increases from 7.2 μW cm⁻¹ K⁻² in PbSnTeSe to 10.3 μW cm⁻¹ K⁻² in PbSn_0.98Cu_0.04PbSe. Consequently, a ZT value of 0.73 at 773 K and an average ZT value of 0.51 at 473-773 K are achieved in p-type PbSn_0.98Cu_0.04PbSe. This work screens out a promising medium-entropy PbSnTeSe alloy thermoelectric and also introduces a novel approach to identifying potential thermoelectric materials within multicomponent lead chalcogenides.