Structural Relaxation Versus Crystallization in a Deeply Undercooled Glass

Ricardo Felipe Lancelotti; Daniel Roberto Cassar; Edgar Dutra Zanotto

Below the glass transition temperature (Tg), the structure of any supercooled liquid (SCL) is frozen when observed in a restricted timespan. This frozen state is denominated glassy state, and a common misconception is that no atomic rearrangement happens in this state. The truth is that the glassy state is transitory; the same processes that take place in a SCL above Tg also happen below it, but they become more and more sluggish as kinetic energy is removed from the system. In fact, at any temperature, this non-equilibrium configuration (called glass) spontaneously and steadily relax towards a metastable configuration of the supercooled liquid. While exploring this concept 70 years ago, Walter Kauzmann questioned what would happen if one could produce a supercooled liquid at temperatures way below Tg. In that case, he observed one unusual situation where the SCL would have the same configurational entropy as the stable crystalline phase, which was later denominated the Kauzmann Paradox. In this talk, we will present new experimental measurements and calculations of sub-Tg structural relaxation for a lithium disilicate glass and compare the relaxation with crystallization kinetics in a range of temperatures below the laboratory Tg in a quest to shed light on this paradox. Our preliminary calculations for this particular glass-forming system indicate that the Kauzmann temperature is unreachable by the SCL because it will crystallize first.