ABSTRACT
It is an intriguing problem of melting curve of Molybdenum (Mo), i.e. there is enormous divergence in melting curves between laser-heated Diamond Anvil Cell (DAC) experiments and Shock-Wave (SW) measurements. One possible reasons is that the melting temperature (Tm) is underestimated in DAC experiments [1], while overestimated in SW experiments [2]. On the other hand, a possible solid-solid phase transition before melting results in the large slope (dT/dP) of the melting curve [3,4]. This issue has attracted much attention in the last few years and is receiving continual attention now. For Mo, the acoustic velocity data by Hixson et al. showed that the longitudinal acoustic velocity disappeared around 390 GPa in SW experiments. And for the liquid material, only the bulk acoustic velocities can be measured. The break of acoustic velocity indicated shock melting [5]. The Tm datum estimated by Hixson et al. is as high as 10000 K. Extrapolating DAC melting data to shock melting pressure, about 5000 K of discrepancies exist. Though Errandonea corrected the SW data by considering 30% superheating [2], the revised Tm (7700 ± 1500 K at 390 GPa) is also much larger than the Tm (below 4000 K) at this pressure extrapolated from DAC experiments. For other refractory metals, the results also show the same problem [6]. In this work, we obtained the melting curve of Mo by using Molecular Dynamic Simulation (MD). It can help us understand the melting law of refractory metals.
