Discovery of quasi-six-coordinated layered phase of PBr3 at high temperature and pressure

Layered trihalides, mainly formed by metal elements and halogens, are promising candidates for spintronic devices and van der Waals heterostructures, but are rarely found in nonmetal halides. Motivated by the purpose of searching for the compelling layered configuration in a covalent system, we performed systemically highpressure experiments to explore the crystal structures in typical PBr3 with diamond anvil cell technique. At room temperature, PBr3 crystallizes into a molecular crystal with orthorhombic symmetry above 0.9 GPa and is found to persist up to at least 43.9 GPa as confirmed by in situ Raman and x-ray diffraction measurements. Strikingly, a novel layered phase with a space group P21/c is observed at & SIM;27.0 GPa and & SIM;1800 K, which is characterized by quasi-six-coordination of P atoms with nearby Br atoms. In addition, first-principles calculations indicate that the unusual coordination of the P atom in P21/c phase is highly correlated with the pressure-induced generation of pnictogen bonds. Our current findings not only expand the understanding of the phase diagram of PBr3, but also show an interesting transformation from molecular crystal to an extended layered phase achieved in a broad range of nonmetal trihalides.