Effect of a Coordination Change on the Strength of Amorphous SiO2

Measurements of the yield strength of SiO₂ glass to pressures as high as 81 gigapascals at room temperature show that the strength of amorphous silica decreases significantly as it is compressed to denser structures with higher coordination. Above 27 gigapascals, as the silicon in amorphous SiO₂ is continuously transformed from fourfold to sixfold coordination, the strength of the glass decreases by more than an order of magnitude. These data confirm theoretical predictions that the mechanical properties of polymerized amorphous silicates are sensitive to pressure-induced structural transformations and suggest that the viscosity of silica-rich liquids decreases significantly at high pressures. Such a change in melt rheology could enhance the processes of chemical differentiation with depth in the Earth's mantle.