Thermal expansion characteristics of Yb-rich high-entropy rare-earth zirconates with defective fluorite structure

Abstract

An emerging trend in advanced thermal barrier coatings is the development of high-entropy ceramics. This study explores a Yb-rich high-entropy rare-earth zirconate synthesized though reverse coprecipitation. The x-ray diffraction and Raman spectrum analysis confirm a homogeneous defective fluorite structure without elemental segregation or secondary phases. The ceramic exhibits a coefficient of thermal expansion of 5.94 × 10−6 K−1 at room temperature, increasing to 11.70 × 10−6 K−1 at 1773 K. The Vickers hardness is measured to be 16.7 GPa. The ab initio calculations confirm the experimental findings, revealing significant local lattice distortion with a broad distribution of metal–oxygen bond lengths and strong nonlocal charge overlap. The substitution of Ce3+, Nd3+, Sm3+, and Eu3+ for Yb3+ forming weaker Ce-O, Nd-O, Sm-O, and Eu-O bonds, which reduce the crystal lattice energy and increase the ion relaxation under thermal vibration, thereby improves the coefficient of thermal expansion of the Yb2Zr2O7 ceramic. This work highlights the key role of bond engineering and lattice distortion in tuning thermal expansion characteristics, providing a robust framework for the rational design of high-entropy materials with optimized properties for high-temperature applications.