Pressure-induced structural changes in boron oxide glass

Glassy B2O3 samples annealed at 300 °C at 10 and 15 kbar were densified by 9% and 11%, respectively. Relaxation by subsequent annealing at ambient pressure restored the original density. The structure of the pressurized samples was determined with x-ray diffraction. A new method was developed for eliminating the Compton scattering by measuring the entire energy spectrum at each scattering angle and fitting it to a superposition of elastic and inelastic scattering derived from the impulse approximation. The measured pair distribution function was fit to a structural model consisting of BO3 triangles linked to form planar ribbonlike structures. It is proposed that densification occurs by buckling of these ribbons. A simple geometrical model of this process can account quantitatively for the changes in density and in the pair distribution function.