Electrochemical Li intercalation and high-pressure response in b-As_yP_1-yalloys: In-situ Raman spectroscopy study

Structural evolution of black Arsenic-Phosphorous (b-As_yP_1-y) alloys with varying Arsenic concentrations were studied under Li intercalation and high-pressure via in-situ Raman spectroscopy. When subjected to electrochemical Li intercalation, a monotonic red shift was observed in all Raman peaks during the initial stage of intercalation due to donor-type charge transfer from Li to b-As_yP_1-y. Above an intercalation threshold, emergence of a new peak, identified as the E_g mode of gray-As with a rhombohedral crystal structure (in contrast to orthorhombic structure of b-As_yP_1-y) was observed undergoing a blue shift, implying hardening of phonon modes due to transformation to a new phase. Further lithiation exhibited a red shift in all Raman modes due to donor type charge transfer to the new structure. Next, b-As_yP_1-y alloys were subjected to high pressure using a Diamond Anvil Cell (DAC). A pressure induced monotonic blue shift was observed in all the Raman modes in these alloys indicating phonon hardening. A partial phase restructuring was observed ∼9 GPa in b-As_0.6P_0.4 with the emergence of the E_g mode of Gray-As and undergoing a blue shift up to ∼9 GPa. b-As_0.8P_0.2 is believed to undergo a complete phase transition around 9 GPa showing a significant change in its Raman spectrum with a dominant E_g mode of Gray-As and diminished P-P peaks.