First-Order Amorphous-Amorphous Transformation in Silica

Molecular simulations predict that a first-order amorphous-amorphous transformation occurs in ${\mathrm{SiO}}_2$ under pressure, analogous to the first-order amorphous-amorphous transformation known to occur in ${\mathrm{H}}_2\mathrm{O}$. At low temperatures the first-order transformation is kinetically hindered, and an amorphous-amorphous transformation occurs instead by gradual spinodal decomposition at higher pressures. We suggest that previous experiments have observed the spinodal decomposition pathway in ${\mathrm{SiO}}_2$ and that the predicted first-order transformation will be observed in experiments carried out at higher temperatures.