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

Weberite-type RE 3 TaO 7 (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. RE 3 TaO 7 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 RE 3 TaO 7 . This study elucidates the dominant mechanisms of properties from the characteristics of crystals and chemical bonds, which are significant for hightemperature applications of tantalates.