Annealing and relaxation in the high-pressure phase of amorphous SiO2

In a recent article [Phys. Rev. Lett. 52, 2379 (1984)] it was reported that irreversible changes occur in the Brillouin spectra of $a-\mathrm{Si}{\mathrm{O}}_2$ that has been subjected to pressures above ∼ 9 GPa. Based on Raman spectra from the recovered samples it was concluded that the new "polymorph" was also amorphous. Here we report on relaxation and annealing effects in this high-pressure form which leave no doubt as to its amorphous nature.