Structural changes in vitreous boron oxide

Brillouin spectroscopy has been used to measure the cornpressional and shear sound velocities of vitreous boron oxide (B2O3) cinder nonhydrostatic and quasi-hydrostatic conditions up to 18.8 and 13.5 GPa, respectively. Our experiments confirmed a pronounced velocity-pressure hysteresis and careful preparation of an anhydrous sample showed that this hysteresis was not due to the presence of water in B2O3. Further; upon decreasing pressure our results are consistent with a discontinuous drop in the compressional and shear velocity near 3 GPa. We believe that this discontinuity may be the result of a structural transition between two vitreous polymorphs.