Phase transitions of enstatite MgSiO3: a molecular dynamics study

Molecular dynamics simulations as a function of increasing pressure starting from the Earthʹs upper mantle phase enstatite MgSiO3 reveal successive phase transitions, first to a new novel intermediate phase, and then to the lower-mantle perovskite phase. While the silicate units are in tetrahedral coordination in the enstatite phase, they are five-coordinated in the new intermediate phase and in octahedral coordination in the lower mantle perovskite phase. Although the occurrence of crystalline five-coordinated silicate phases is somewhat rare, the new intermediate phase obtained through the simulations is found to be crystalline. The simulations have enabled a microscopic visualization of the key mechanisms of these transitions and provide useful insights about the variations in the vibrational properties due to these changes in silicate coordination.