Ultralight supertetrahedral aluminum: Stability at various temperatures

Ab initio molecular dynamics simulations of the structural stability of the allotropic supertetrahedral ultralight form of aluminum at different temperatures have shown that supertetrahedral aluminum remains structurally stable up to the temperature of 200 K. When being heated to 225 K, supertetrahedral aluminum melts, followed by a liquid-to-solid phase transition and formation of the face-centered-cubic (fcc) structure. The transformation of supertetrahedral aluminum into fcc aluminum is accompanied by an energy release of 4260 kJ/kg. Taking into account its stability at temperatures below 200 K, supertetrahedral aluminum would not float in water because water is solid at this temperature, but it would float in liquid nitrogen. Impact statement Recently predicted novel allotropic modification of aluminum—supertetrahedral aluminum brought worldwide attention in both the scientific community and the press. This new material constructed from Al 4 tetrahedra is predicted to be a very light solid with a density equal to 0.61 g/cm 3 . Such material is of particular interest to scientific and engineering communities due to its various potential applications because it is a metal and at the same time it has extremely low density. Moreover, this material could guide the design of other new ultralight materials. In this article, we conducted a long ab initio molecular dynamics simulation (up to 325 ps) at various temperatures and showed that ultralight supertetrahedral aluminum remains structurally stable up to the temperature of 200 K according to our calculations. This is a reasonably high temperature for experimental verification of this remarkable material, which is lighter than water. At higher temperature (225 K) supertetrahedral aluminum melts, followed by a liquid-to-solid phase transition and formation of the face-centered-cubic structure. Graphical abstract