Vibrational Analysis Study of Aluminum Trifluoride Phases

Abstract

The vibrational modes of three solid AlF₃ phases (α, β, and amorphous high surface area AlF₃) are investigated. Calculations have been performed using hybrid exchange correlation functionals to determine the equilibrium geometries and Γ-point phonon frequencies for the α-AlF₃ and β-AlF₃ phases. The calculated optical modes are in excellent agreement with experiment. The IR absorption of the amorphous, glasslike high surface area (HS)-AlF₃ is also discussed. Deconvolution of the broad envelope of IR stretches and bending vibrations identifies the components of the observed broad band. From the IR vibrational spectrum it has been shown that both short-range and medium-range disorder are present within HS-AlF₃. Structural phase transitions are identified by their phase transition temperature T_c, measured by thermal analysis.