Prediction of the material with highest known melting point fromab initiomolecular dynamics calculations

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

“…reported a similar trend to Rudy’s results5 but with slightly higher values (Table 1), however their values were obtained from thermodynamic calculations. The trend obtained in our work is similar to the one predicted by Hong and van de Walle9 with HfC 0.81 having the highest melting temperature, TaC 0.88 the lowest, and with a local maximum for Ta 0.8 Hf 0.2 C.…”

“…Nevertheless, the current melting temperature of HfC 0.98 remains the highest of the series. The presence of a local maximum melting temperature for mixed Hf-Ta carbides has been shown to be accompanied by a spectral emissivity effect, consistent with the existence, recently proposed by Hong and van de Walle9, of a link between the melting behaviour and the Fermi level position in this kind of compounds. This should boost further experimental research on Ta-Hf-C-N compositions that might display even higher melting temperatures than those assessed for the ternary Ta-Hf-C system, in line with Hong and van de Walle’s theoretical predictions.…”

“…The reason must lie with the dependence of the NSE on composition and wavelength and no definite conclusions can be drawn on the absolute melting/solidification temperatures without a direct in-situ measurement of NSE, an extremely challenging task when one considers the extreme temperatures involved. On the other hand, the observed link between sample emissivity and the existence of a local maximum melting/solidification temperature can be taken as an additional, experimental hint in favour of the hypothesis held by Hong and van de Walle9, that the position of the Fermi level in Ta-Hf-C compositions has a direct effect on their melting point. This should certainly encourage further experimental research in line with Hong and van de Walle’s theoretical prediction, based also on considerations on the liquid phase entropy, that mixed Ta-Hf-C-N compositions might display even higher melting points than those assessed for the ternary Ta-Hf-C system.…”

“…In addition, the work by Gusev8 reports a calculated phase diagram (CALPHAD) for the TaC-HfC system in which the melting temperatures of the single member carbides are higher than those of the solid solutions, with TaC as the highest melting compound at 4275 K and 55 K higher than HfC. More recently, Hong and van de Walle9 predicted the melting temperatures using density functional theory (DFT) and their calculations suggest that the melting temperature of HfC 0.81 is 3962 K, higher than TaC 0.88 at 3830 K. Also these calculations were consistent with a local maximum within the solid solutions, for a composition close to Ta 0.8 Hf 0.2 C at 3920 K. The work of Hong and de Walle was particularly useful, in that it identified precise physical mechanisms behind the effects of carbon hypostoichiometry and alloying on the melting temperature of a given composition. In addition, HfC 0.56 N 0.38 was reported as the compound with the highest melting temperature at 4141 K. In summary, the uncertain and contradictory results on the melting points reported suggest that: (i) thanks to the entropic contribution of lattice defects to reducing the free energy of the solid phase, slightly hypostoichiometric monocarbides might have melting temperatures higher than their solid solutions789; (ii) because of the Fermi energy position in the mixed carbides, a maximum melting temperature within the solid solutions (TaC-HfC) might exist469.…”

The initial stages of melting of graphene between 4000 K and 6000 K

“…They recently identified a novel HfN 0.38 C 0.51 alloy with a remarkable predicted 4398 K melting point. 13 We note that the bulk crystal graphite does not melt at room pressure, but instead sublimes at roughly 4000 K (we note that the triple point for graphite is 0.01 GPa, 4200 K, where solid-liquid-vapor coexist). 14 …”