The phases of cerium above 5 GPa have been studied using angle-dispersive powder diffraction techniques. The phase obtained between 5 and 12 GPa at room temperature with filings of Ce has a monoclinic, distorted-fcc structure with four atoms in a $C$-face-centered unit cell. Heating to 373 K for many hours yields the known $\alpha$-U phase. With a single cut piece as a sample, the $\alpha$-U phase is obtained at room temperature.

• Received 8 May 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.3884