Reverse-martensitic hcp-to-fcc transformation in technetium under shock compression

The equation of state and principal shock Hugoniot of the elemental technetium to 285 GPa were predicted from ab initio molecular dynamics simulations using Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 300 and 4500 K and densities ranging from ρ ≃ 11.4 to 16.7 g/cm3. A temperature-driven hcp → fcc reverse-martensitic phase transformation is predicted to occur at T ≃ 2800 K in Tc bulk subjected to shock loading. The results from dynamic compression were compared to recent diamond-anvil-cell hydrostatic compression data and cold-curve predictions using the density functional theory. The melting curve of Tc is predicted from Lindemann's criterion.