Dominant mechanisms of thermo-mechanical properties of weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates toward multifunctional thermal/environmental barrier coating applications

• Published in: Acta materialia 2024-05, Vol.270, p.119857, Article 119857
• Main Authors: Chen, Lin, Hu, Mingyu, Wang, Jiankun, Li, Baihui, Feng, Jing
• Format: Article
• Language: English
• Subjects: Mechanical properties; Oxygen ion conductivity; T/EBCs; Tantalates; Thermal conductivity; Thermal expansion anisotropy
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2024.119857

Weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates have been studied as multifunctional thermal/environmental barrier coating materials with working temperatures above 1500 K. This study proposes the dominant mechanisms of their thermo-mechanical properties. The relative ionicity of the RE-O bonds increased with increasing RE+3 ionic radius, which weakened the bond strength and led to decreases in Young's modulus and hardness. A model was proposed to derive the high-temperature thermal conductivity based on the relationship between the phonon thermal conductivity and temperature, and the thermal radiative conductivity was estimated. RE3TaO7 exhibited a lower thermal conductivity than other fluorite-related oxides because its weak bond strength could slow down the phonon speed and enhance the an-harmonic vibrations of the lattices. At low temperatures, the RE atomic weight was a better descriptor of the thermal conductivity than the RE+3 ionic radius, and which could aid in further regulating the thermal conductivity. The thermal expansion coefficients of the different axes were affected by both RE-O and Ta-O bonds when weak RE-O bonds dominated the linear thermal expansion. The low oxygen ion conductivity derived from the strong covalent Ta-O bonds, which increased the activation energy for oxygen hopping in lattices of RE3TaO7. This study elucidates the dominant mechanisms of properties from the characteristics of crystals and chemical bonds, which are significant for high-temperature applications of tantalates. The dominant mechanisms of thermo-mechanical properties of weberite-type RE3TaO7 ceramics are elucidated from aspects of crystal structures and chemical bonds. The relatively low modulus is derived from the high relative ionicity of RE-O bonds, which weakens their bonding strength, and a model is proposed to predict the high-temperature thermal conductivity. This work finds out that RE atomic weight is a better descriptor of thermal conductivity than RE+3 ionic radius, when the weak RE-O bonds dominate thermal expansion performance of RE3TaO7 tantalates. The low thermal conductivity and oxygen ion conductivity, high TECs, and excellent phase stability indicate that weberite-type RE3TaO7 tantalates are promising multifunctional T/EBCs. The uncovered mechanisms of properties are essential for their applications and further regulations. [Display omitted]