A latent heat method to detect melting and freezing of metals at megabar pressures.

The pressure dependence of melting temperature and latent heat of fusion for metals provide simple and useful tests for theories of melting, as well as important constraints for the modeling of planetary interiors. Here, we present a new experimental technique that reveals the latent heat of fusion of a metal sample compressed inside a diamond anvil cell. The technique combines microsecond-timescale pulsed electrical heating with an internally-heated diamond anvil cell for the first time. Further, we use the technique to constrain the melting curve of platinum to a relatively narrow temperature range from $\sim 3000$ K at 34 GPa to $\sim 4500$ K at 107 GPa, thermodynamic conditions that are between the steep and shallow experimental melting curves reported previously. Upper bounds on the entropy and volume of fusion are also determined at high pressure: $\Delta S_m \leq 21$ J/mol/K and $\Delta V_m \leq 0.35$ cm$^3$/mol and at $86 \pm 6$ GPa.