The non-coincidence effect in glass

Polarization dependent inelastic light scattering as a function of temperature was carried out on various oxide glasses including NBS-710 glass, calcium-aluminosilicates and lanthanum-gallogermanate glasses. In their low frequency Raman spectra featuring the Boson peak, we have observed a non-coincidence effect for the first time in these glasses by comparing their polarized and depolarized Boson peak maximum intensity frequencies. This effect is the observation that the peak frequency for the anisotropic Boson peak maximum, Ianiso(ω), is at a different frequency value than that of the isotropic Boson peak maximum, Iiso(ω). Thus, we define the non-coincidence effect (NCE) as δωN.C. = ωaniso − ωiso, with ωaniso and ωiso being the Boson peak intensity maximum frequencies for the anisotropic and isotropic Raman line, respectively. A plausible explanation for this effect can be based on an intramolecular–intermolecular viewpoint and the resulting dominant attractive or repulsive bonding picture. Changes in the peak frequency for the anisotropic peak maximum occur because of intermolecular anharmonicity. Ianiso (or IVH) detects the angular dependence of the intermolecular potential while Iiso reflects only the spherically symmetric average value of the potential. The existence of the non-coincidence effect in glasses is the further evidence of molecular clusters or ordered domain formation and is in agreement with the universal concept of intermediate range order in glass.