Design and experimental investigation of potential low-thermal-conductivity high-entropy rare-earth zirconates

• Published in: Journal of advanced ceramics Vol. 13; no. 8; pp. 1132 - 1142
• Main Authors: Liu, Lu, Dong, Hongying, Zhang, Peng, Wang, Shaokun, Qi, Haolei, Ding, Mengyu, Li, Zhefeng, Bai, Yu, Ma, Wen
• Format: Journal Article
• Language: English
• Published: Tsinghua University Press 01.08.2024
• Subjects: composition design; high-entropy ceramics; rare-earth zirconate (he-re2zr2o7); thermal barrier coatings (tbcs); thermal conductivity
• ISSN: 2226-4108; 2227-8508
• DOI: 10.26599/JAC.2024.9220923

Developing new high-entropy rare-earth zirconate (HE-RE2Zr2O7) ceramics with low thermal conductivity is essential for thermal barrier coating materials. In this work, the average atomic spacings, interatomic forces, and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A2B2O7 crystal structure were calculated by density functional theory. These three physical qualities, as vectors, characterize the corresponding rare-earth elements. The distance between two vectors quantitatively describes the difference between two rare-earth elements. For greater differences between two rare-earth elements, the disorder degree of HE-RE2Zr2O7 is greater, and therefore, the thermal conductivity is lower. According to the theoretical calculations, the thermal conductivity of the ceramics gradually increases in the order of (Sc0.2Y0.2La0.2Ho0.2Yb0.2)2Zr2O7, (Sc0.2Ce0.2Nd0.2Eu0.2Gd0.2)2Zr2O7, (Sc0.2Y0.2Tm0.2Yb0.2Lu0.2)2Zr2O7, and (Sc0.2Er0.2Tm0.2Yb0.2Lu0.2)2Zr2O7. Using the solution precursor plasma spray method and pressureless sintering method, four types of HE-RE2Zr2O7 powder and bulk samples were prepared. The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure. The thermal conductivities of the sintered HE-RE2Zr2O7 bulk samples ranged from 1.30 to 1.45 W·m−1·K−1 at 1400 °C, and their differences were consistent with the theoretical calculation results. Among the ceramics, (Sc0.2Y0.2La0.2Ho0.2Yb0.2)2Zr2O7 had the lowest thermal conductivity (1.30 W∙m−1∙K−1, 1400 °C), highest thermal expansion coefficient (10.19×10−6 K−1, 200–1400 °C), highest fracture toughness (1.69±0.28 MPa∙m1/2), and smallest brittleness index (3.03 μm−1/2). Therefore, (Sc0.2Y0.2La0.2Ho0.2Yb0.2)2Zr2O7 is considered to be an ideal candidate material for next-generation thermal barrier coating applications.