Advanced thermal/environmental barrier coatings of high-entropy rare earth disilicates tuned by strong anharmonicity of Eu2Si2O7

Abstract

Advancing thermal/environmental barrier coating (TEBC) materials with integrated thermal-mechanical functions is paramount for safeguarding SiC-based ceramic matrix composites (CMCs) in high-efficiency gas turbines. Herein, we employ a synergistic approach, combining density functional theory (DFT) methods and combinatorial chemistry techniques, to design high-performance and low-cost RE₂Si₂O₇ (RE = rare earth elements) TEBC materials tailored for enhanced compatibility with SiC-based CMCs. Expanding on phase stability of alloying pure RE₂Si₂O₇, the investigation extends to the mechanical and thermal properties of solid solution systems, including Er_1/2Y_3/4Yb_3/4Si₂O₇, Gd_1/4Er_1/4Y_3/4Yb_3/4Si₂O₇, and Eu_1/4Er_1/4Y_3/4Yb_3/4Si₂O₇. The solid solution systems exhibit a major reduction in lattice thermal conductivity relative to their pure counterparts, achieving ultralow values of 0.25 to 0.39 W m⁻¹ K⁻¹ at 1500 K. Furthermore, the coefficients of thermal expansion (CTE) of these solid solutions are precisely tuned within the desired range for SiC (4.4 to 5.5 × 10⁻⁶ K⁻¹), while maintaining good mechanical properties. In particular, the addition of Eu₂Si₂O₇ demonstrates to be an important variable to the tuning of CTE and lattice thermal conductivity by leveraging its strong anharmonicity, presenting a pioneering avenue for fine-tuning material properties. In summary, this research not only identifies promising TEBC materials with superior thermal properties, but also introduces a valuable computational material design methodology for the rapid discovery of complex materials for harsh environments.