Properties ofB2O: An unsymmetrical analog of carbon

The compound ${\mathrm{B}}_2$O has been proposed to be an isoelectronic analog of carbon. The high-temperature, high-pressure syntheses of both ‘‘graphitelike’’ and ‘‘diamondlike’’ phases of ${\mathrm{B}}_2$O have been reported, although the material has not been well characterized. We have applied the density-functional total-energy method to two candidate structures for this material. Both structures are based on a diamond lattice, but differ in the direction of stacking of the boron and oxygen planes. In order to find the equilibrium structures, we have relaxed both the internal coordinates and the unit-cell parameters. We find that one structure, proposed previously, is unstable, while the other has a bulk modulus of approximately 2 Mbar, comparable to SiC.