Exploring the phase-space of network-forming liquids: liquid-liquid transitions, fragility and chemical disorder

Studies of liquids, particularly during compression or supercooling, have indicated the existence of phase transitions in the liquid state, and the first experimental evidence for liquid-liquid phase transition has recently been reported for molten phosph orus. A first order transition between two liquids of different densities is also consistent with experimental findings and molecular dynamic simulations for a variety of substances, including water, silica and carbon. Moreover, the coexistence of two pha ses, that are chemically identical but have different density and local structure, were observed in quenched Y2O3-Al2O3 melts. All these reports have encouraged the search for polymorphic phase transitions in li quids and glasses. The project will allow us to follow up our previous efforts (see e.g. Nature 2001, 414, 622) and to elucidate details in the complex chemistry and physics of liquid GeSe2. In addition the project will give us the opportunity to initiate a study of a new system that we expect show anomalous behaviour in the liquid state. Focus are given to an exploration of the phase space of network-forming liquid and glassy GeSe2, SiS2 and SiSe2. New polyamorphs are sought. In addition focus will be given to the relationship between fragility, fragility transitions and chemical disorder.