Novel Boron-rich Phosphides with High Hardness, Large Strain, and Magnetism

Boron-rich compounds have attracted much attention due to their interesting structures and excellent properties. Here, we performed an extensive study on the different B-P stoichiometries under pressure by combining a particle swarm optimization method with first-principles calculations. At 1 atm, BP and B₆P are thermodynamically stable, while other stoichiometries are metastable. Under pressure, BP and B₆P remain stable relative to constituent pure solids up to 80 GPa, while other stoichiometries become unstable at relatively low pressures. A new Cmca B₆P is predicted with the lowest energy at 1 atm and shows higher shear strain than the R3̅m structure, which is known to be more resistant to brittle fracture than B₄C. Moreover, the predicted Pm B₈P is a magnetic semiconductor with a magnetic moment of 1 μ_B. All these boron-rich phosphides are hard materials. The present results enrich the B-P phase diagram and promote extensive research on their excellent properties.