Structure and mechanical properties of cubic BC2N crystals within a random solid solution model

Within a random solid solution model based on diamond lattice, the formation energies, lattice constants, and elastic properties of BC2N crystals were calculated using first-principles methods. We found that the degree of BN–C2 mixture defined by the ratio of bond contents is the key for the lattice parameter, relative stability, and physical properties in the BC2N solid solution. BC2N crystals with the most probable degree of mixture possess larger lattice parameters and less elastic moduli with respect to cubic-BN, and the high formation energy can be compensated by the contribution of configuration entropy under high-temperature conditions. The present model can explain the controversial experimental results on BC2N crystals synthesized under different conditions.

Research highlights
► Random solid solution model for BC2N crystals.
► Degree of mixture as the key parameter.
► High formation energy can be compensated by the configurational entropy at high Tpatients.