Phonon Properties of Bulk Violet Phosphorus Single Crystals: Temperature and Pressure Evolution

Violet phosphorus, the most stable phosphorus allotrope, has been successfully produced recently. Phonon properties of layered structures are important characteristic features to provide their structural and chemical information. Raman spectroscopy is an easy, nondestructive, and effective characterization path to obtain phonon properties of elemental layered structures. However, no reliable data are available due to the lack of pure violet phosphorus crystals or rational lattice structures. The successful synthesis of violet phosphorus single crystals and further acquisition of its lattice structure give the possibility for the phonon properties of violet phosphorus. The phonon properties of violet phosphorus single crystals have been demonstrated both theoretically and experimentally in this work. The vibrational modes have been assigned. The evolution of Raman features between 103 and 833 K and 0-25 GPa has been studied. The first-order temperature coefficients for Tg, Ptub, and S[P9]-[P9] of violet phosphorus are much larger than those of the reported layered structures. The violet phosphorus has been demonstrated to transfer into A7 black phosphorus (rhombohedral) (>8.5 GPa) and then to a simple cubic one (>13.6 GPa). Only black phosphorus was obtained when the pressure was released back to ambient conditions.