Vibrational Properties of Pristine and Lithium‐Intercalated Black Phosphorous under High‐Pressure

Structural evolution of Li‐intercalated and pristine black phosphorous (BP) under high‐pressure (up to ≈8 GPa) is studied using in situ Raman spectroscopy. Even though both materials show a monotonic blueshift of the out‐of‐plane vibrational mode (A1g) with pressure, Li‐intercalated BP do not show a blueshift until a threshold pressure (2.4 GPa) is reached to compensate the structural expansion caused by intercalation. However, the in‐plane modes (B2g and A2g) in each sample respond differently. In the mid‐pressure region, they both show redshifts which in Li‐intercalated BP is also followed by abrupt blueshifts. Such behavior indicates pressure‐induced structural reorganizations inside the material. Computational modeling reveals the existence of a process of P─P bond breaking and reforming in the system due to the redistribution of intercalated Li atoms under pressure. This work shows the significance of combined effect of pressure and intercalation on structural changes in the search for new phases of BP and other two‐dimensional (2D) materials. Out‐of‐plane Raman modes of pristine and lithium intercalated black phosphorous (BP) show a monotonic blue‐shift with increasing pressure. In‐plane modes of pristine black phosphorous show a red‐shift in the mid‐pressure region whereas intercalated BP show a red‐shift followed by an abrupt blue‐shift. These changes of in‐plane vibrational modes are evidence for pressure‐induced structural reorganization in black phosphorus.