Structural basis and bonding mechanisms for mechanical and thermal properties of rare earth oxides

Abstract

In this work, we have investigated the mechanical and thermal properties of rare earth sesquioxides A/B/C-RE₂O₃ (RE = La to Lu) by using the first-principles calculation. It is shown that the lattice parameters of RE₂O₃ generally decrease with the rare earth atomic number owing to the lanthanide contraction. Compared to [REO₆] polyhedrons, all [REO₇] polyhedrons present the longer RE-O bonds and the lower energies in spite of different polymorphs. Meanwhile, the elastic moduli show clear increasing tendency from A-RE₂O₃ to C-RE₂O₃ and from La₂O₃ to Lu₂O₃, which may originate from the stronger covalancy or weaker ionicity according to P-V-L chemical bond theory. In addition, the theoretical minimum thermal conductivity is predicted in range of 0.57–0.61 W·m¹·K⁻¹, 0.68–0.72 W·m⁻¹·K⁻¹, and 0.59–0.73 W·m⁻¹·K⁻¹ for A-, B-, and C-RE₂O₃, respectively. Further analysis about temperature-dependent thermal conductivity indicates that the chemical bonds dominate the increasing thermal conductivity with RE elements while the structural complexity determines the difference between three phases. This work provides a comprehensive database on structural, mechanical and thermal properties of RE₂O₃, but also shields light on the exploration of rare-earth-containing oxides with complex structure for potential applications including thermal/environmental barrier coatings.