Ultrapressure equation of state of cerium metal to 208 GPa

We report static pressure compression of cerium metal to 208 GPa (volume co mpression V/V-0 = 0.37) in a diamond anvil cell at room temperature. Cerium is unique in the 4f elements because of proximity of the f shell to the Fe rmi energy and related phase transformations induced by pressure. The energ y-dispersive x-ray diffraction studies were carried out on cerium metal to 208 GPa using a synchrotron x-ray source and an internal copper pressure st andard. A collapsed body centered tetragonal phase is found to be stable to the highest pressure with axial ratio remarkably constant at 1.680 +/- 0.0 06 in the 90-208 GPa pressure range in excellent agreement with theory. Cer ium is thus isostructural and isoelectronic with 5f -band metal thorium at ultrapressures. We present equation of state parameters, which describe the compression of cerium to ultrapressures. (C) 1999 American Institute of Ph ysics. [S0021-8979(99)03404- 0].