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

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 A(2)B(2)O(7) 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)(2)Zr2O7, (Sc0.2Ce0.2Nd0.2Eu0.2Gd0.2)(2)Zr2O7, (Sc0.2Y0.2Tm0.2Yb0.2Lu0.2)(2)Zr2O7, and (Sc0.2Er0.2Tm0.2Yb0.2Lu0.2)(2)Zr2O7. 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<middle dot>m(-1)<middle dot>K-1 at 1400 degrees C, and their differences were consistent with the theoretical calculation results. Among the ceramics, (Sc0.2Y0.2La0.2Ho0.2Yb0.2)(2)Zr2O7 had the lowest thermal conductivity (1.30 W center dot m(-1)center dot K-1, 1400 degrees C), highest thermal expansion coefficient (10.19x10(-6) K-1, 200-1400 degrees C), highest fracture toughness (1.69 +/- 0.28 MPa center dot m(1/2)), and smallest brittleness index (3.03 mu m(-1/2)). Therefore, (Sc0.2Y0.2La0.2Ho0.2Yb0.2)(2)Zr2O7 is considered to be an ideal candidate material for next-generation thermal barrier coating applications.