bcc lead at 109 GPa: Diffraction studies to 208 GPa

Energy-dispersive x-ray diffraction studies have been made on lead to 208 GPa with platinum as a pressure marker material using a synchrotron source. A new phase transition from hcp Pb(II) to Pb(III) begins at 111 GPa on compression and the reverse transition begins at 107 GPA on decompression. It is shown that Pb(III) has the body-centered-cubic crystal structure. The hcp-to-bcc phase transformation in Pb is sluggish at room temperature and unusually large hysteresis is associated with the completion of this transformation on compression as well as on decompression.