High entropy oxides as next-generation thermal barrier coatings – A processing perspective

High-entropy oxides (HEOs) are emerging as promising candidates for next-generation thermal barrier coatings (TBCs) owing to configurationally stabilized phases, sluggish diffusion kinetics, and intrinsically low thermal conductivity arising from mass and lattice disorder. However, most studies remain focused on compositional exploration, while processing, an equally critical determinant of coating performance, has received limited attention. This review adopts a processing-focused perspective on HEO-based TBCs, emphasizing the shift from bulk-centric validation toward coating-relevant studies. Existing work is largely confined to powders or bulk-sintered materials, with few systematic coating-level investigations. Powder synthesis is dominated by solid-state and wet-chemical routes, which face challenges in scalability and process consistency. Consequently, reported HEO coatings are primarily deposited by atmospheric plasma spraying, where splat-based architectures decouple bulk behaviour from coating performance. Solution precursor plasma spraying (SPPS) is highlighted as a single-step route enabling compositionally flexible, powder-free deposition that can accelerate the exploration of process–structure–property relationships.