Pressure-Induced Polyamorphic Transition and Stepwise Ordering to Superhard B-Doped Diamond-like BC3

Abstract

We employ constant-pressure ab initio molecular dynamics simulations to investigate the pressure-induced phase transformations of amorphous BC3, which initially possesses a graphite-like layered structure. Our simulations reveal a first-order polyamorphic transition marked by a significant volume collapse and an increase in atomic coordination from a predominantly sp(2) network to a dense, tetrahedrally coordinated sp(3) network. Subsequent thermal annealing of the high-pressure phase uncovers a multi-step ordering process involving a metastable paracrystalline intermediate that bridges the high-density amorphous state and a thermally induced boron-doped diamond-like phase. All high-pressure phases are quenchable to ambient conditions, importantly retaining their semiconducting electronic structures across these transformations. Mechanical characterization demonstrates substantial stiffening, with bulk moduli ranging similar to 252 to 323 GPa. These findings illuminate novel and accessible routes to superhard semiconducting BC3 phases stabilized by pressure and temperature, with the boron-doped diamond-like phase identified as a metastable superhard semiconductor that is thermodynamically favored over the amorphous precursor but kinetically accessible only via the stepwise pathway described. This offers promising directions for advanced material design under extreme conditions.