A high-pressure polymorph of boron oxide, B2O3-P212121, has been obtained in a laser-heated diamond anvil cell at 50(3) GPa after heating boron trioxide to a temperature of Tmax ≤ 2500(300) K. The crystal structure was determined from synchrotron single crystal X-ray diffraction and was confirmed by a combination of density functional theory (DFT) calculations and experimental Raman spectroscopy. Experimental- as well as DFT-data confirm the non-centrosymmetric/non-polar space group P212121. The structural model of B2O3-P212121 is in agreement with an earlier DFT-based crystal structure prediction. The crystal structure is characterized by corner-sharing BO4 tetrahedra with covalent B-O bonds. Our experimental Raman data show that B2O3-P212121 can be recovered under ambient conditions.
Spahr et al. (Thu,) studied this question.