Pressure-Induced Metastable Phase

Reversible Pressure-Induced Partial Phase Transition in Few-Layer Black Phosphorus

Anirban et al. have demonstrated the existence of reversible pressure-induced partial phase transition in few-layer Black Phosphorus (BP),  probed by high-pressure Raman spectroscopy. The study reveals the existence of a metastable state, where both Black Phosphorus (orthorhombic) and Blue Phosphorus (rhombohedral) phases can coexist. 
Nano Letters, 2020
https://dx.doi.org/10.1021/acs.nanolett.0c01784  
Pressure-Induced Metastable Phase