Dual-site cationic disorder engineering for ultralow amorphous-like thermal conductivity in thermal barrier coatings

Abstract

Developing thermal barrier coatings (TBCs) with ultralow thermal conductivity and substrate-matched thermal expansion remains a long-standing challenge for enhancing aero-engine efficiency and durability. In this study, we report a single-cation dual-site occupation strategy in a high-entropy pyrochlore (A₂B₂O₇) oxide, formulated as (La_1−xY_x)₂(Zr_0.25Sn_0.125Ce_0.125Nb_0.250Y_0.250)₂O₇ (denoted as La_1−xY_x-HE), in which Y³⁺ simultaneously occupies both A and B lattice sites. Remarkably, Y³⁺ serves as the smallest cation suitable for the A site while also being the largest cation suitable for the B site, creating an extreme cation size mismatch-induced lattice disorder. This dual-site disorder effectively enhances phonon scattering, leading to excellent thermal insulation performance, together with a well-matched thermal expansion coefficient. Notably, La_0.500Y_0.500-HE exhibits an ultralow amorphous-like thermal conductivity of 1.06 W m⁻¹ K⁻¹, approximately half that of conventional/commercial YSZ, while maintaining a compatible thermal expansion coefficient of 10.01 × 10⁻⁶ K⁻¹, which aligns well with that of the substrate. Meanwhile, it exhibits excellent mechanical properties, including a Vickers hardness of 9.86 GPa and a Young's modulus of 133.4 GPa. The dual-site disorder strategy provides an effective pathway for designing next-generation TBCs with superior thermal insulation performance.