Melting of the rare earth metals and f-electron delocalization

Melting curves for Pr, Nd, Sm, Gd, and Y were measured in a diamond-anvil-cell to nearly 100 GPa and 4000 K. f-electron volume collapses are observed as triple points for Pr (24 GPa and 1400 K) and Gd (65 GPa and 3100 K). These pressures coincide with the volume collapses observed at room temperature. For Nd and Sm, the f-electron volume collapse has not been observed at room temperature but appears at approximately 2000-2500 K as a broad minimum in the melting curve, similar to that of Ce, near 50 GPa (Nd) and 70 GPa (Sm). The melting curve of Y goes smoothly along the entire rare earth sequence.