Bonding changes across the α-cristobalite→stishovite transition path in silica

The transformation of the chemical bonding network of SiO2 across the pressure-induced α-cristobalite→stishovite phase transition is rigorously analyzed using the topology of the electron localization function (ELF). Under a martensitic approach, the simultaneous and concerted atomic displacements can be theoretically modeled by means of a transition path of P41212 symmetry. For the parent and the product phases, as well as for selected structures of this mechanism, the characterization of ELF critical points and the integration of basin properties of the ELF attractors have allowed us to study how the nature of the bonding network and the charges and volumes of shells, bonds and lone pairs evolve along this transformation. The change in the Si environment from tetrahedral to octahedral coordination is accompanied by a significant increase in the bond ionicity and by a decrease in the crystal compressibility due to the greater electron density of the oxygen valence shell in the stishovite phase.