Alloy scattering to optimize carrier and phonon transport properties in PbBi₂S₄ thermoelectric

Ternary PbBi₂S₄ compound with crustal S-rich element and low lattice thermal conductivity is considered as a potential thermoelectric candidate. However, its inferior thermoelectric properties are rooted in the low electrical transport performance. Generally, enhancing electrical transport performance (power factor, PF) primarily entails optimizing the interdependent relationship between carrier mobility μ (linked to electrical conductivity σ) and effective mass m∗ (related to Seebeck coefficient S). In this work, we introduce the strategy of alloy scattering to independently enhance S without weakening μ and simultaneously reduce thermal conductivity, leading to a synergetic optimization of electron and phonon in PbBi₂S₄ thermoelectric. Heavy Sn alloying in PbBi₂S₄ presents uniform and orderly distribution on Pb sites as unclosed by the atomic-scale crystal structure observation. These massive Sn atom serves as scattering centers and turns the electron scattering mechanism to be dominated by alloy scattering, thus resulting in a ∼33% increment of S in Pb_0.6Sn_0.4Bi₂S₄. Meanwhile, Sn alloying aggravates phonon scattering further lowering lattice thermal conductivity and reaching an extremely low value of 0.34 W⋅m⁻¹·K⁻¹ at 773 K. Finally, a maximum zT of 0.68 at 773 K is obtained in Pb_0.6Sn_0.4Bi₂S₄, which is ∼ 45% higher than the pristine matrix. This study proves that the strategy of alloy scattering is effective in improving overall electrical transport properties as well as reducing lattice thermal conductivity, which paves a new way to develop high-performance thermoelectric materials.