High-pressure response of vibrational properties of b-As (x) P1-x : in situ Raman studies

The structural evolution of black arsenic-phosphorous (b-AsxP1-x) alloys with varying arsenic concentrations was investigated under hydrostatic pressure using in situ Raman spectroscopy. Highpressure experiments were conducted using a diamond anvil cell, which revealed pressure-induced shifts in vibrational modes associated with P-P bonds (A(g)(1), A(g)(2), B-g(2)), As-As bonds (A(g)(1), A(g)(2), B-g(2)), and As-P bonds in b-AsxP1-x alloys. Two distinct pressure regimes were observed. In the first regime (region I), all vibrational modes exhibited a monotonic upshift, indicating phonon hardening due to hydrostatic pressure. In the second regime (region II), As0.4P0.6 and As0.6P0.4 alloys displayed a linear blueshift (or negligible change in some modes) at a reduced rate, suggesting local structural reorganization with less compression on the bonds. Notably, the alloy with the highest As concentration, As0.8P0.2, exhibited anomalous behavior in the second pressure regime, with a downward shift observed in all As-As and As-P Raman modes (and some P-P modes). Interestingly, the emergence of new peaks corresponding to the Eg mode and A(1g) mode of the gray-As phase was observed in this pressure range, indicating compressive strain-induced structural changes. The anomalous change in region II confirms the formation of a new local structure, characterized by elongation of the P-P, As-As, and As-P bonds along the zigzag direction within the b-AsxP1- x phase, possibly near the grain boundary. Additionally, a gray-As phase undergoes compressive structural changes. This study underscores the significance of pressure in inducing structural transformations and exploring novel phases in two-dimensional materials, including b-AsxP1- x alloys.