Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

A second melting temperature occurs at a temperature Tn+ higher than T-m in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to Tn+. Recent MD simulations show full melting at Tn+ = 1.119T(m) for Zr, 1.126T(m) for Ag, 1.219T(m) for Fe and 1.354T(m) for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at T-g and the nucleation temperatures T-nG of glacial phases are successfully predicted below and above T-m. The glass transition temperature T-g increases with the heating rate up to Tn+. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating Tn+ and T-nG around T-m shows that T-nG cannot be higher than 1.293T(m) for Tn+= 1.47T(m). The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T-g and T-nG above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to Tn+ because the antibonds are broken by homogeneous nucleation of bonds.