Synthesis and thermal behavior of rare-earth-niobate ceramics with fluorite structure

• Published in: Ceramics international 2024-11, Vol.50 (21), p.42299-42308
• Main Authors: Cao, Jiaying, Zhang, Min, Ma, Xingyun, Zhao, Siting, Jiang, Ting, Wen, Wei
• Format: Article
• Language: English
• Subjects: Defective fluorite structure; Glass-like thermal conductivity; High-entropy ceramics; Rare-earth niobates; Thermal barrier coatings
• ISSN: 0272-8842
• DOI: 10.1016/j.ceramint.2024.08.075

High-entropy ceramics have potential as thermal barrier coatings (TBCs) and a new way to reduce thermal conductivity. (Gd0.25Ho0.25Er0.25Yb0.25)3NbO7 (4RE3NbO7) and (Ho0.33Er0.33Yb0.33)3NbO7 (3RE3NbO7) rare-earth niobates with disordered defective fluorite structures were synthesized using the solid-phase method. They show prominent phase stability at 1400 °C and excellent chemical compatibility with Al2O3 at 1200 °C. The SEM and EDS results show that the samples have a dense and uniform grain structure, and the average grain size is less than 2 μm. The uniform distributions of rare earth cations further indicate the successful realization of equimolar ratio doping. Compared to yttrium oxide-stabilized zirconia (YSZ) materials, both 4RE3NbO7 and 3RE3NbO7 ceramics have glass-like thermal conductivity, and the thermal conductivity of 4RE3NbO7 ceramics (1.032–1.177W/m·K, 25–800 °C) was lower than that of 3RE3NbO7 ceramics (1.058–1.183W/m·K, 25–800 °C). In addition, 4RE3NbO7 and 3RE3NbO7 exhibited comparable coefficients of thermal expansion (9.78–9.61 × 10−6 K−1, 1200 °C) and enhanced mechanical properties (Hv = 7.14–9.07 GPa, KIC = 2.02–1.62 MPa m1/2). The results of this study motivate a follow-up study on niobate high entropy ceramics with desirable properties.