Three-dimensional buckled honeycomb boron lattice with vacancies as an intermediate phase on the transition pathway from |[alpha]|-B to |[gamma]|-B

We report the discovery of novel metastable boron allotropes, called hex-B ν , using the crystal structure search method. First-principles calculations reveal that hex-B ν shows not only dynamical, mechanical stability but also structural flexibility under high pressures and high temperatures. We suggest a new pressure-induced transition pathway from α-B12 to γ-B28 under extreme conditions, in which our discovered allotropes can act as intermediate phases. This work provides a possible solution to the long-standing fundamental question on the phase transition mechanism between boron allotropes.