Raman and Infrared Studies of Coupled PO4−3 Vibrations

Abstract

The vibrations of PO4 −3 ions in single crystals of hexagonal Ca10(PO4)6F2 have been observed by means of polarized Raman scattering and polarized infrared reflectance. The T 2 (ν 3 ) and T 2 (ν 4 ) Raman vibration frequencies are each observed to split in accord with the predictions of the factor group of the unit cell. The optically active vibrational modes are also observed, and the anisotropy of the extraordinary ray frequencies have been measured. The observations are analyzed in terms of dipole–dipole interionic forces using Ewald dipole summation techniques to account for the entire phosphate lattice. Qualitative agreement between the dipole model and experiment is achieved. The roles of short‐range forces and background dielectric shielding are discussed.