W0016: Fragility and Polyamorphism in Aluminate Liquids

Aluminate liquids are often highly fragile, with very non-Arrhenian relaxation. We have studied local structural configurations responsible for the fragile behavior via spectroscopic techniques (NMR, IR, Raman) and ion dynamics simulations in liquids and glasses along the CaO-AlO join. The results indicate that the next-nearest-neighbour (NNN) metal packing is highly sensitive to temperature, and is likely responsible for the non-Arrhenian behavior. During a study of supercooled liquids in the system YO-AlO, we observed occurrence of a first-order phase transition between two liquid phases with the same composition , but with different structure and density. The transition occurred close to the glass transformation of both liquids, so that both liquid phases were quenched to metastably coexisting glasses. Such density-driven liquid-liquid phase transformations and polyamorphism have been predicted to occur for other, simple systems. We have physically separated the coexisting glassy phases for structural and physical properties characterization, and will discuss their density and enthalpic relaxation. We will also discuss implications of the liquid-liquid transition for the rheology in the supercooled liquid state. Both Al coordination and NNN metal rearrangements likely play a role in the YO-AlOliquid behavior, in which the first order phase transition is observed between a high density, high temperature liquid and a low density liquid at lower temperature.