Electrochemical Li intercalation in b-AsyP1−y alloys: In-situ Raman spectroscopy study

Abstract

Structural evolution of b-AsyP1−y alloys with varying As concentration, y was studied during Li-intercalation using in-situ Raman spectroscopy. A monotonic redshift of all the vibrational modes corresponding to P-P bonds (A1g, A2g, B2g), As-As bonds (A1g, A2g, B2g), and As-P bonds of all the samples was observed during the initial stages of the intercalation process due to the softening of each mode caused by the intercalation driven donor-type charge-transfer from Li to b-AsyP1−y. The emergence of a new peak identified as the Eg mode of gray As, above an intercalation threshold, is indicative of the presence of an intercalation-driven structural phase segregation process. Further, A1 g mode of gray As emerging after this intercalation threshold lies in close proximity of Ag2 Raman mode of b-AsyP1−y. All the peaks beyond the intercalation threshold show an upshift due to the co-existence of gray As with b-AsyP1−y alloys causing strain and thus hardening of the phonon modes. In the sample with the highest As concentration phase segregation takes place during the synthesis process. Computational modeling reveals the co-existence of gray As in the b-AsyP1−y alloys with high As concentrations. It also confirms the existence of a local structural segregation taking place at a critical Li concentration during the intercalation process. This work shows the significance of intercalation on structural changes in the search for new phases of b-AsyP1−y alloys.