Dissociation of Liquid Silica at High Pressures and Temperatures

Liquid silica at high pressure and temperature is shown to undergo significant structural modifications and profound changes in its electronic properties. Temperature measurements on shock waves in silica at 70--1000 GPa indicate that the specific heat of liquid SiO₂ rises well above the Dulong-Petit limit, exhibiting a broad peak with temperature that is attributable to the growing structural disorder caused by bond breaking in the melt. The simultaneous sharp rise in optical reflectivity of liquid SiO₂ indicates that such dissociation causes the electrical and therefore thermal conductivities of silica to attain metalliclike values of 1--5×10⁵ S/m and 24--600 W/m·K, respectively.