Design and experimental investigation of potential low-thermal-conductivity high-entropy rare-earth zirconates
Lu Liu, Hongying Dong, Peng Zhang, Shaokun Wang, Haolei Qi, Mengyu Ding, Zong‐Ge Li, Yu Bai, Wen Ma
Abstract
Developing new high-entropy rare-earth zirconate (HE-RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>) 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 A<sub>2</sub>B<sub>2</sub>O<sub>7</sub> crystal structure were calculated by density functional theory. These three physical qualities, as vectors, characterise the corresponding rare-earth elements. The distance between the two vectors quantitatively describes the difference between two rare-earth elements. For greater difference between two rare-earth elements, the disorder degree of HE-RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> is higher, and therefore the thermal conductivity is lower. From theoretical calculation, the thermal conductivity of the ceramics gradually increases in the order (Sc<sub>0.2</sub>Y<sub>0.2</sub>La<sub>0.2</sub>Ho<sub>0.2</sub>Yb<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>, (Sc<sub>0.2</sub>Ce<sub>0.2</sub>Nd<sub>0.2</sub>Eu<sub>0.2</sub>Gd<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>, (Sc<sub>0.2</sub>Y<sub>0.2</sub>Tm<sub>0.2</sub>Yb<sub>0.2</sub>Lu<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>, and (Sc<sub>0.2</sub>Er<sub>0.2</sub>Tm<sub>0.2</sub>Yb<sub>0.2</sub>Lu<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>. Using the solution precursor plasma spray method and pressureless sintering method, four types of HE-RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> powder and bulk samples were prepared. The samples all showed a single defective fluorite structure with uniform distribution of the elements and a stable phase structure. The thermal conductivities of the sintered HE-RE<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> bulk samples were in the range 1.30–1.45 W·m<sup>−1</sup>·K<sup>−1</sup> at 1400 °C, and their differences were consistent with the theoretical calculation results. Among the ceramics, (Sc<sub>0.2</sub>Y<sub>0.2</sub>La<sub>0.2</sub>Ho<sub>0.2</sub>Yb<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> showed the lowest thermal conductivity (1.30 W∙m<sup>−1</sup>∙K<sup>−1</sup>, 1400 °C), highest thermal expansion coefficient (10.19 × 10<sup>−6</sup> K<sup>−1</sup>, 200–1400 °C), highest fracture toughness (1.69 ± 0.28 MPa∙m<sup>1/2</sup>), and smallest brittleness index (3.03·μm<sup>−1/2</sup>). Therefore, (Sc<sub>0.2</sub>Y<sub>0.2</sub>La<sub>0.2</sub>Ho<sub>0.2</sub>Yb<sub>0.2</sub>)<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> is considered to be an ideal candidate material for next-generation thermal barrier coating applications.