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.