Ti‐rich Medium‐Entropy‐Alloy Thin Films as Robust Diffusion Barriers for Thermoelectric Generators

Chemical interdiffusion at interfaces is inevitable and often detrimental in devices subjected to temperature gradients or electrical currents with Joule heating. Identifying diffusion barriers that ensure mechanical durability, stable electrical conduction, and resistance to intermetallic formation remains a key challenge. Here, the medium‐entropy alloys (MEAs) guided by thermodynamic engineering as robust alternatives to conventional Ni layers are exploited. By experimentally establishing phase equilibria at 1273 K, a single‐phase β ‐Ti region within the Ti 70 ‐Al–Cr–V system is identified. Microstructural and mechanical assessments further delineates an optimal compositional window for Ti‐rich alloys suitable as diffusion barriers. Selected Ti 70 AlCrV alloys exhibit low density and moderate hardness an advantageous balance that minimizes weight while ensuring mechanical integrity. To evaluate functionality, Ni and Ti‐rich MEA thin films are deposited on n ‐type PbTe substrates and integrate into single‐leg thermoelectric devices. Remarkably, Ti‐rich MEA barriers impart superior thermal stability, sustaining conversion efficiencies above 1.91% under a 200 K temperature gradient. Significantly, the single‐phase Ti‐rich MEA thin film effectively suppresses interfacial intermetallic growth, attributed to their ability to curb diffusion‐driven reactions. This work advances the design of MEAs and highlights their promise as diffusion barriers for scalable thermoelectric technologies.