Orthorhombic boron oxide under pressure: In situ study by X-ray diffraction and Raman scattering

High-pressure phase of boron oxide, orthorhombic β-B₂O₃, has been studied in situ by synchrotron X-ray diffraction to 22 GPa and Raman scattering to 46 GPa at room temperature. The bulk modulus of β-B₂O₃ has been found to be 169(3) GPa that is in good agreement with our ab initio calculations. Raman and IR spectra of β-B₂O₃ have been measured at ambient pressure; all experimentally observed bands have been attributed to the theoretically calculated ones, and the mode assignment has been performed. Based on the data on Raman shift as a function of pressure, combined with equation-of-state data, the Grüneisen parameters of all experimentally observed Raman bands have been calculated. β-B₂O₃ enriched by ¹⁰B isotope has been synthesized, and the effect of boron isotopic substitution on Raman spectra has been studied.