Interdiffusion-suppressing glassy medium-entropy alloy for stable skutterudite thermoelectric single legs

Phase diagram engineering, coupled with the medium-entropy alloy (MEA) concept, identifies a β -Ti single-phase region in the quaternary Ti–Al–Ni–Cr system, enabling rational diffusion-barrier design for CoSb 3 thermoelectric single legs. Compared with conventional crystalline Ni films, a glassy single-phase MEA film (Ti 70 Al 10 Ni 5 Cr 15 ) exhibits suppressed interdiffusion with CoSb 3 , owing to restricted diffusion pathways associated with its quasi-amorphous structure. This effectively prevents the formation of detrimental intermetallic compounds commonly observed at Ni/CoSb 3 interfaces. Device-level measurements over Δ T = 50–350 K show comparable peak conversion efficiency but markedly improved cycle-to-cycle stability for MEA-coated single legs, consistent with reduced interfacial resistance and minimized parasitic losses. Interfacial characterization by characterized by Transmission Electron Microscopy (TEM) and synchrotron-based X-ray Fluorescence (XRF), and compositional line profiling confirms a chemically abrupt and well-preserved Cu/solder/MEA/CoSb 3 architecture, with no detectable intermetallic formation even after exposure to a hot-side temperature of 623 K. These results demonstrate that the glassy MEA thin film simultaneously meets the requirements for both contact compatibility and diffusion-barrier functionality by maintaining a single-phase structure while suppressing fast grain-boundary diffusion, thereby stabilizing thermoelectric interfaces under operating conditions.