Melting of the alkaline-earth metals to 80 GPa

The melting curves of Mg, Ca, Sr, and Ba were measured in a laser-heated diamond-anvil-cell to 80 GPa. Systematic changes in the melting slopes were found to be associated with the phase transitions observed at room temperature and with the increasing d-electron character of these metals. Mg, Ca, and Sr show a flattening of the melting curve (dT/dP~0) when they melt from the bcc structure, most likely due to the small volume change between bcc and melt structures. Sr exhibits a melting minimum at 40 GPa and 2000 K which is coincident with the presence of complex structures observed at room temperature. Above 20 (40) GPa, Ba (Sr) shows a continuous rise in the melting temperature apparently related to the completion of the sp→d electron transfer.