Abstract:The inferior thermal stability of p-type skutterudites and their electrical contacts has severely limited the reliability of skutterudite-based thermoelectric devices. In this work, a dual-phase multi-principal element alloy interlayer, CoFeNiMo0.75, is engineered via adequate Mo alloying to establish a multiple diffusion barrier effect while maintaining thermal expansion matching. Mo dissolved in the FCC matrix intensifies lattice distortion to hinder elemental diffusion, while the dispersed dendritic Mo-rich μ-phase precipitates exhibit weak reactivity and increase the effective diffusion-path tortuosity. Owing to this dual-phase synergistic mechanism, the CoFeNiMo0.75/La0.8Ti0.1Ga0.1Fe3.3Co0.7Sb12 interface demonstrates exceptional thermal stability. After aging at 823 K for 600 h, the interfacial contact resistivity increased only from ~2.51 μΩ·cm2 to ~3.22 μΩ·cm2, following parabolic kinetics with an ultralow rate constant of ~0.028 μΩ·cm2·h-1/2, while the shear strength remained largely stable at ~16 MPa. These results showcase the potential of the dual-phase strategy in achieving robust, multi-level diffusion barriers for next-generation thermoelectric interfaces.