Static ultra‐high pressure study of lanthanide and actinide metals using a diamond‐anvil cell

Structural phase transformations in lanthanides and actinides were investigated as a function of pressure up to 300 GPa at room temperature. Except in Ce and Pr, no large volume changes were noticed for these metals as they went through several phase changes. The appearance of a bct ultra‐high pressure phase in Ce, Sm, Th, and possibly in Np, raises the possibility that the ultimate high pressure structure for the 4f and 5f metals may be the bct structure. On the other hand, it is also possible that this is a precursor to another close‐packed structure at even higher pressure.