I studied systems composed of silicon, aluminum, and oxygen in my master thesis (with Jürgen Horbach and Kurt Binder). These systems are glass formers: If you cool them quickly enough, all the atoms freeze whereever they are, without forming a crystal structure. If you look at such a system´s structure, it is indistinguishable from that of a liquid.

I continued a molecular dynamics study on the slowing down caused by cooling in my master thesis.

The figure shows a special feature of these mixtures: Aluminum atoms (green) are surrounded by four oxygens (red), to form tetrahedra. Same for the silicon atoms (yellow). But the aluminum tetrahedra tend to connect to other tetrahedra with an entire edge, not just a corner (as for the silicon tetrahedra). Oxygens involved in such a double connection often have three, not two, bonds (as with the two oxygens in the middle). The simulations showed that the system’s dynamics are enhanced when more aluminum oxide, hence more such structures, are in the system.

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