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Relaxational and Low‐Wavenumber Vibrational Dynamics of Strong Glass FormersB 2 O 3 andGeO 2 Probed by Raman Scattering
Author(s) -
Brodin A.,
Torell L. M.
Publication year - 1996
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199610)27:10<723::aid-jrs31>3.0.co;2-8
Subject(s) - wavenumber , relaxation (psychology) , fragility , raman spectroscopy , glass transition , raman scattering , intensity (physics) , scattering , dynamics (music) , molecular dynamics , materials science , limiting , chemistry , condensed matter physics , molecular physics , thermodynamics , optics , physics , computational chemistry , composite material , acoustics , mechanical engineering , psychology , social psychology , engineering , polymer
Low‐wavenumber Raman scattering results are presented on the structural dynamics of two network‐forming glasses: the moderately strong glass former B 2 O 3 and the extremely strong GeO 2 . Studies were performed from temperatures ca . 10 K to above their respective glass transition temperatures ( T g ≈526 K for B 2 O 3 and 800 K for GeO 2 ). Two distinct spectral contributions were detected, related to vibrational and fast relaxational dynamics, respectively, and conventionally referred to as the boson peak (BP) and quasi‐elastic scattering (QS). The fast relaxation spectrum is discussed in terms of the mode coupling theory (MCT), which has been shown to describe fragile glass formers successfully. A quantity proportional to the fast relaxation strength may be deduced from the integral intensity of QS relative to BP of the spectra. It turns out that for T T g . Moreover, the experimentally obtained value of the MCT exponent a , describing the shape of the fast dynamics, greatly exceeds the limiting value ( a =0.395) of the theory, the deviation increasing with increasing strength of the system ( a≈ 0.7 for B 2 O 3 and 0.9 for GeO 2 ). The difference between the two glasses is discussed in terms of their differences in fragility as manifested in the behaviour of the specific heat around T g .