Signature of a polyamorphic transition in the THz spectrum of vitreous   GeO2
  The THz spectrum of density fluctuations, $S(Q, \omega)$, of vitreous GeO$_2$ at ambient temperature was measured by inelastic x-ray scattering from ambient pressure up to pressures well beyond that of the known $\alpha$-quartz to rutile polyamorphic (PA) transition. We observe significant differences in the spectral shape measured below and above the PA transition, in particular, in the 30-80 meV range. Guided by first-principle lattice dynamics calculations, we interpret the changes in the phonon dispersion as the evolution from a quartz-like to a rutile-like coordination. Notably, such a crossover is accompanied by a cusp-like behavior in the pressure dependence of the elastic response of the system. Overall, the presented results highlight the complex fingerprint of PA phenomena on the high-frequency phonon dispersion. 
Alessandro Cunsolo, Yan Li, Chaminda N. Kodituwakku, Shibing Wang,   Daniele Antonangeli, Filippo Bencivenga, Andrea Battist...
cond-mat.dis-nn cond-mat.mtrl-sci cond-mat.stat-mech physics.chem-ph