Melting of aluminum, molybdenum, and the light actinides

A semi-empirical model was used to explain why the measured melting curves of molybdenum, and the other bcc transition metals, have an unusually low slope (dT/dP{approx}0). The total binding energy of Mo is written as the sum of the repulsive energy of the ions and sp-electrons (modeled by an inverse 6th power potential) and the d-band cohesive energy described by the well known Friedel equation. Using literature values for the Mo band width energy, the number of d-electrons and their volume dependence, we find that a small broadening of the liquid d-band width ({approx}1%) leads to an increase in the stability of the liquid relative to the solid. This is sufficient to depress the melting temperature and lower the melting slope to a value in agreement with the diamond-anvil cell measurements. Omission of the d-band physics results in an Al-like melting curve with a much steeper melt slope. The model, when applied to the f-electrons of the light actinides (Th-Am), gives agreement with the observed fall and rise in the melting temperature with increasing atomic number.

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