VOIDS IN NETWORK-FORMING LIQUIDS AND THEIR INFLUENCE ON THE STRUCTUREAND DYNAMICS

A Voronoi analysis is applied to clarify the origin of certain unusual physical properties of three representative network-forming ionic liq uids: SiO2, ZnCl2, and BeCl2. In each of these fluids, the local struc ture under ambient pressure comprises a tetrahedral unit of anions aro und cations which link together to form a network. The Voronoi analysi s is used to characterize the empty space (voids) within the network. Despite sharing the same local tetrahedral arrangement, the network pr operties of the three liquids differ markedly on an intermediate lengt h scale and this leads to significant differences in the properties of the voids. It is shown how the void analysis helps to interpret the a nomalous behaviour of the diffusivity in SiO,, which over a certain ra nge of density increases with increasing density, and to clarify the o rigin of the intermediate range order in the atomic positions, as seen in the much discussed first sharp diffraction peak (or prepeak) in di ffraction data.