Comparison Of The High-Pressure Behavior Of The Cerium Oxides Ce2o3 And Ceo2

The high-pressure behavior of Ce2O3 was studied using angle-dispersive x-ray diffraction to 70 GPa and compared with that of CeO2. Up to the highest pressure Ce2O3 remains in the hexagonal phase (space group 164, P (3) over bar2/m1) typical for the lanthanide sesquioxides. A theoretically predicted phase instability for 30 GPa is not observed. The isothermal bulk modulus and its pressure derivative for the quasihydrostatic case are B-0 = 111 +/- 2 GPa, B-0' = 4.7 +/- 0.3, and for the case without pressure-transmitting medium B-0 = 104 +/- 4 GPa, B-0' = 6.5 +/- 0.4. Starting from ambient-pressure magnetic susceptibility measurements for both oxides in highly purified form, we find that the Ce atom in Ce2O3 behaves like a trivalent Ce3+ ion (2.57 mu(B) per Ce atom) in contrast to previously published data. Since x-ray emission spectroscopy of the L gamma (4d(3/2) -> 2p(1/2)) transition is sensitive to the 4f -electron occupancy, we also followed the high-pressure dependence of this line for both oxides up to 50 GPa. No change of the respective line shape was observed, indicating that the 4f -electron configuration is stable for both materials. We posit from this data that the 4f electrons do not drive the volume collapse of CeO2 from the high-symmetry, low-pressure fluorite structure to the lower-symmetry orthorhombic phase.