Melting of lead under high pressure studied using second-scale time-resolved x-ray diffraction

The high pressure and high temperature phase diagram of lead has been studied up to 80 GPa and 3700 K in a laser-heated diamond anvil cell. Melting and solid-solid phase transitions have been followed with a second scale by in situ synchrotron time-resolved x-ray diffraction. The detection of the x-ray signal scattered by the liquid was used as an objective criterion for melting. We evidenced that the melting phenomenon in a diamond anvil cell has a typical lifetime that can be as low as 1 s. Unlike a previous laser-heated diamond anvil cell study, the measured melting curve is in agreement with melting points detected using dynamic compression and confirms the predictions of ab initio calculations. The pressure-temperature conditions of the hcp-bcc phase transition have been measured, and the hcp-bcc-liquid triple point has been located around 39 GPa and 2400 K.