Medium-Range Order in Permanently DensifiedSiO2andGeO2Glass

Amorphous material has a characteristic anomaly called a boson peak in the low-energy phonon density of states. Boson peaks of permanently densified ${\mathrm{SiO}}_2$ and ${\mathrm{GeO}}_2$ glass retrieved from various high pressures $P_0$ were measured by Raman scattering at ambient pressure. In ${\mathrm{SiO}}_2$ glass the energy starts to increase at $P_0=12\mathrm{}\mathrm{GPa}$ and reaches 40% higher energy at $P_0=18\mathrm{}\mathrm{GPa}$, while in ${\mathrm{GeO}}_2$ glass the boson peak energy increases at $P_0=6\mathrm{}\mathrm{GPa}$, but thereafter the energy stays nearly constant. These boson peak energies maintain nearly inverse proportionality to the correlation lengths estimated from the widths of the x-ray first sharp diffraction peaks.