A. Yb 2 O 3 Cubic (C-type, Ia 3), monoclinic (B-type, C2/m), and hexagonal (A-type, P 3m1) phases are well known three polymorphs of rare-earth sesquioxides . For Yb 2 O 3 , the cubic phase is stable at ambient pressure, whereas monoclinic and hexagonal phases are stable at high pressures . The monoclinic-phase nanoparticles have been synthesized via a combustion process .