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

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<middle dot>m1<middle dot>K-1, 0.68-0.72 W<middle dot>m-1<middle dot>K-1, and 0.59-0.73 W<middle dot>m-1<middle dot>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.