Anomalies of the fast relaxation dynamics at T{sub g} in strong glass formers
- Chalmers Univ. of Technology, Goeteborg (Sweden). Dept. of Physics
Structural dynamics of two network forming glasses, B{sub 2}O{sub 3} and GeO{sub 2}, has been investigated by Raman scattering over a wide temperature range from {approximately}10 K to above the respective glass transition temperatures (T{sub g} {approx} 526 K for B{sub 2}O{sub 3} and 800 K for GeO{sub 2}). The spectra are analyzed in terms of two distinct contributions, related to vibrational and fast relaxational dynamics, respectively, and conventionally referred to as the boson peak (BP) and quasielastic scattering (QS). 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{sub g} the so-obtained QS intensity of the two glasses is similar and smoothly temperature dependent, and can qualitatively be described by e.g., the defect model or the soft potential model. As T{sub g} is passed, there is a pronounced change in behavior and dramatic differences between the two systems are observed. Thus, the fast relaxational dynamics is obviously affected by T{sub g}, a finding which is in contrast to the predictions of the mode coupling theory (MCT) of a single crossover temperature T{sub c} > T{sub g}. Moreover, the experimentally obtained value of the MCT exponent a, describing the shape of the fast dynamics, is by far exceeding the limiting value (a = 0.395) of the theory, the deviation increasing with the strength of the system (a = 0.7 for B{sub 2}O{sub 3} and {approx}0.9 for GeO{sub 2}). The observed difference between the two glasses is discussed in terms of the fragility of the system manifested in jumps in the specific heat temperature dependences.
- OSTI ID:
- 580848
- Report Number(s):
- CONF-961202-; ISBN 1-55899-359-2; TRN: IM9807%%57
- Resource Relation:
- Conference: 1996 Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 2-6 Dec 1996; Other Information: PBD: 1997; Related Information: Is Part Of Structure and dynamics of glasses and glass formers; Angell, C.A. [ed.] [Arizona State Univ., Tempe, AZ (United States)]; Ngai, K.L. [ed.] [Naval Research Lab., Washington, DC (United States)]; Kieffer, J. [ed.] [Univ. of Illinois, Urbana, IL (United States)]; Egami, T. [ed.] [Univ. of Pennsylvania, Philadelphia, PA (United States)]; Nienhaus, G.U. [ed.] [Univ. of Ulm (Germany)]; PB: 530 p.; Materials Research Society symposium proceedings, Volume 455
- Country of Publication:
- United States
- Language:
- English
Similar Records
An alternative explanation of the change in T-dependence of the effective Debye-Waller factor at T{sub c} or T{sub B}
The liquid-glass transition in a strong glassformer