Equivalence of the Boson Peak in Glasses to the Transverse Acoustic van Hove Singularity in Crystals

Abstract

We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.

Stress-Induced Modification of the Boson Peak Scaling Behavior

“…Without exception, available results are all in agreement [3,4,[13][14][15][16][17][18][19][20][21][22]: the BP shifts towards higher frequencies and decreases in intensity when the sample becomes stiffer (increase of elastic constants). Recently, it has been proposed to quantitatively test the role played by the changes in the elastic properties by scaling the BP data with the Debye frequency, a quantity defined by the elastic medium.…”

“…This anomalous feature appears in the signal detected by several techniques, such as inelastic neutron scattering [1], calorimetry [2], nuclear inelastic scattering [3,4], Mössbauer [5], Raman [6] and hyperRaman spectroscopy [7,8]. Despite the long-standing interest in this characteristic feature, its origin still re- mains a source of controversy [9][10][11][12][13][14][15][16].…”

“…The question of whether such a scaling is able to generate a master curve of the data, and hence, the variations of g(ω) can be explained in terms of elastic medium transformations is still highly debated. So far, the accumulated evidence is apparently in favor of opposite views: on one hand, the BP evolution in sodium silicate glasses (cooled [13], compressed [16], hy-perquenched [3] and permanently densified samples [4]) and in an epoxy-amine mixture during chemical vitrification [19] is controlled by changes in the system's elasticity, according to the Debye scaling law; on the other hand, the BP variations in network forming glasses like silica and GeO 2 upon cooling [14,15,23], in permanently densified silica [17], and in few polymers under pressure [20,21] are stronger than the elastic medium transformation, and the Debye scaling does not work. In light of such controversial results the question we face is the following: Do these results really conflict, or rather there is a general explanation in terms of the elastic properties of the systems?…”

Structural Irreversibility and Enhanced Brittleness under Fatigue in Zr-Based Amorphous Solids

“…Its origin has been linked to transverse vibrational modes associated with defective structures [16], to local vibrational modes of clusters [17], and to crossover dynamics of local and acoustic modes [18]. More recently it was proposed that the boson peak is analogous to the acoustic van Hove singularity in crystals [19][20][21]. The excess vibrational density of states, as determined both from the neutron inelastic scattering and C P measurements displays a maximum of a few milli-electron Volts (meV) (of the order of 10 −12 s).…”

Condensed Matter Physics Using Nuclear Resonant Scattering

“…[106][107][108] In addition, many important studies using the features of nuclear resonant inelastic scattering spectroscopy have been performed, e.g., on nanoparticles, [109][110][111][112][113][114] thin films, [115][116][117][118][119][120][121] quasi crystals, 122) clathrates, 123,124) superconductors, [125][126][127][128] filled skutterudites, [129][130][131][132] and glass. 133,134) The nuclear resonance scattering method can be applied to not only solids but also liquids. The element-specific diffusion constant of Fe ions in HCl solution 135) and the dynamics of Fe ions in Nafion membranes, 136,137) which are used as ion-exchange membranes, were measured using this method.…”