Lattice dynamics study of (Gd 1−x Yb x ) 2 O 3 (x=0.11) at high pressure

In this study, we report an experimental investigation of (Gd 1−x Yb x ) 2 O 3 under high pressure by means of Raman scattering measurements complemented with ab initio calculations in pure Gd 2 O 3. Raman spectroscopy of compressed (Gd 1−x Yb x ) 2 O 3 (x = 0.11) revealed a first phase transition from the cubic Ia 3̅ phase (C-type) to the monoclinic C2/m phase (B-type) at 6.2 GPa followed by a second phase transition towards the trigonal P 3̅ m1 phase (A-type) at 9.8 GPa. This sequence of phase transitions is different to that previously reported for pure Gd 2 O 3. A phase transition from the trigonal to the monoclinic phase is observed on downstroke, so the B-type phase remains metastable at room pressure, as observed in all C-type rare earth sesquioxides. Theoretical calculations have helped to identify the different polymorphs and to assign the symmetry of the observed first-order Raman-active modes in the three phases. The pressure coefficients of the Raman-active modes of the three phases followed under pressure have been reported and compared to those of pure Gd 2 O 3 and other rare-earth sesquioxides.