摘要
Under the condition of high pressure, the cations of silicon in oxide or silicate minerals can occur migration phenomenon from low coordination number polyhedra to high coordination number polyhedra with increasing pressure. This migration is due to the change with radius ratio of cations to anions. Under high pressure the ionic radii of oxygen and silicon have been calculated for different SiO2 polymorphs. It is indicated that the ionic radius of oxygen decreases gradually with increasing pressure, but the cation radius of silicon increases with increasing pressure and the occurrence of phase transitions. The phenomenon may be due to the transitions from ionic compounds to metallic phases under high pressures.