Phonon-electron decoupling enables ultralow thermal conductivity in YCl3 & Te-doped Mg3.2Sb1.5Bi0.5

Abstract

Mg₃Sb₂-based thermoelectric materials are widely recognized as highly promising functional materials due to their cost-effectiveness, non-toxicity, and environmental friendliness. In this study, a synergistic doping strategy involving YCl₃ & Te was implemented, achieving a peak ZT value of 1.83 at 723K in the Mg_3.2Sb_1.5Bi_0.49Te_0.01 + 1 % YCl₃ composition. First-principles calculations demonstrate that YCl₃ & Te co-doping precisely modulates the Fermi level position, facilitating n-type conduction behavior. Simultaneously, the substitution of Sb by Cl induces lattice contraction, while the doping-driven "avoided crossing" effect collectively suppresses phonon transport, resulting in an ultralow lattice thermal conductivity of 0.27 W m⁻¹ K⁻¹. Moreover, the incorporation of YCl₃ & Te significantly improves the deformation resistance of Mg₃Sb₂, enhancing its suitability for subsequent material processing and device integration. Finite element analysis predicts that the energy conversion efficiency of the Mg_3.2Sb_1.5Bi_0.49Te_0.01 + 1 % YCl₃ sample exceeds 11 % under a temperature gradient of 423K. This work provides new insights into the phonon-electron decoupling mechanism in Mg₃Sb₂-based thermoelectric materials through the synergistic regulation of band engineering and phonon engineering.