In situ measurement of the structure of supercooled oxide liquids

Abstract

This paper will describe the results of in situ high-energy X-ray measurements performed on stable and supercooled oxide liquids using containerless techniques. As will be discussed in the companion paper (Weber et al.), the use of an aerodynamic levitator furnace with laser heating allows the structures of refractory oxide liquids to be probed. Because of the contactless nature of this sample environment liquids can be deeply supercooled, and this provides opportunities to study the metastable structures of supercooled liquids. Of particular interest are the so-called fragile liquids that depart from Arrhenius-law viscosity behaviour and that, by definition, have temperature-dependent structures. The focus of this paper is the study of two oxide systems, MgO-SiO 2 and Al 2 O 3 -SiO 2 . These two liquids have highly disordered stable liquid structures that differ substantially from the structures of the equivalent glasses. We present data showing how these structures change when supercooled and demonstrate dramatic changes in short-range (coordination number) and intermediate-range order during vitrification. These data have been collected by isothermal measurement and also fast quenching methods using the recently developed method of rapid acquisition using a Perkin Elmer amorphous silicon flat panel detector; this gives a large Q coverage for incident energies of >115 keV. The rapid data acquisition enables the vitrification process to be observed directly.