The high-pressure behavior of the cubic C-type ${\mathrm{Yb}}_2$${\mathrm{O}}_3$ was investigated by ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ Mössbauer spectroscopy and energy-dispersive x-ray diffraction. The room-temperature x-ray-diffraction data show that C-${\mathrm{Yb}}_2$${\mathrm{O}}_3$ transforms to the monoclinic B-type structure above 13 GPa. The equation of state of both C- and B-type phases was derived from these experiments. Mössbauer measurements up to 20 GPa were carried out at 4.2 K using a Merrill-Bassett-type anvil cell. They confirm the occurrence of a pressure-induced phase transition. The pressure (volume) dependence of the lattice and 4f contributions to the electric-field gradient at the ${\mathrm{Yb}}^{3+}$ ions in the C phase is discussed.

• Received 17 January 1995

DOI:https://doi.org/10.1103/PhysRevB.51.12187