The high-pressure behavior of $\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_3$ was studied using angle-dispersive x-ray diffraction to 70 GPa and compared with that of $\mathrm{Ce}{\mathrm{O}}_2$. Up to the highest pressure $\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_3$ remains in the hexagonal phase (space group 164, $P\overline{3}2/m1)$ 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 $B_0=111\pm 2\mathrm{GPa},B_0^{\prime }=4.7\pm 0.3,$ and for the case without pressure-transmitting medium $B_0=104\pm 4\mathrm{GPa},B_0^{\prime }=6.5\pm 0.4$. Starting from ambient-pressure magnetic susceptibility measurements for both oxides in highly purified form, we find that the Ce atom in $\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_3$ behaves like a trivalent $\mathrm{C}{\mathrm{e}}^{3+}$ ion ($2.57{\mu }_{\mathrm{B}}$ per Ce atom) in contrast to previously published data. Since x-ray emission spectroscopy of the $L\gamma$ $\left(4d_{3/2}\to 2p_{1/2}\right)$ 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 $\mathrm{Ce}{\mathrm{O}}_2$ from the high-symmetry, low-pressure fluorite structure to the lower-symmetry orthorhombic phase.

• Received 24 August 2015

DOI:https://doi.org/10.1103/PhysRevB.93.064106