The liquid-glass transition in a strong glassformer

Based on light and neutron scattering observations we describe the relaxation dynamics of a strong glassformer, B2O3. The experimental information is compared with predictions of the mode coupling theory (MCT) of the liquid-glass transition in order to test whether its success in describing fragile systems can be extended also to strong glassformers. The data show the predicted two-step relaxation, and the time decay follows qualitatively the MCT functional form. Also, there is convincing evidence of some cross-over temperature in the dynamics that may be identified as the critical temperature Tc of MCT. There are however some distinct differences. Tc is not as sharply defined in B2O3 and it is at a considerably higher temperature (Tc = 1.6Tg) than in fragile ones (Tc = 1.2 Tg). We suggest this to be characteristic for strong glassformers in general due to their broader glass transformation range. Moreover, a strong vibrational contribution, the boson peak, affects the high frequency dynamics which results in significant deviations from the MCT master curve. In strong systems the boson peak is generally more pronounced. Therefore, a successful description of the liquid-glass transition in strong systems has to address the influence of vibrational modes on the relaxation dynamics.