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Achieving high thermoelectric performance in metal sulfide PbSnS2 through strain-mediated lone-pair expression amplification and multi-band conduction
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DOI：10.1039/D6TA01797E.png)
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Abstract
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PbSnS2 is a low-cost and earth-abundant metal sulfide that exhibits promising thermoelectric performance; characterized by low lattice thermal conductivity associated with stereochemically active 5s2 (Sn) and 6s2 (Pb) lone-pair electrons. In this work; strain-driven modulation of lone-pair activity; phonon transport; lattice thermal conductivity; and thermoelectric performance in layered PbSnS2 is systematically revealed by first-principles calculations. Biaxial strain ranging from −2% (compressive) to +2% (tensile) progressively weakens interatomic bonding and enhances lone-pair stereochemical activity. This enhancement leads to a simultaneous suppression of particle-like and wave-like heat transport through phonon softening; reduced phonon group velocities; and strengthened three-phonon scattering; resulting in a marked reduction of lattice thermal conductivity from 2.0 to 1.22 W m−1 K−1 at 300 K. At −2% compressive strain; the presence of pronounced multi-band features near the Fermi level gives rise to an unusual decoupling between electrical conductivity and the Seebeck coefficient. Consequently; the power factor reaches 3.23 mW m−1 K−2 under −2% compressive strain; nearly twice that achieved under +2% tensile strain; and delivers a substantially enhanced thermoelectric figure of merit with a maximum zT of 1.18 at 900 K. These results establish strain engineering as an effective and dynamic strategy for optimizing thermoelectric performance in PbSnS2 and provide general design guidelines for lone-pair-active metal sulfide thermoelectrics.
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