Abstract
The vibrations of phosphate (PO −3 4) ions in single crystals of hexagonal Ba 5(PO 4) 3F (B-FAP) have been investigated by means of polarized Raman scattering and compared to Raman frequencies observed in fluoroapatite analogs Sr 5(PO 4) 3F (S-FAP) and Ca 5(PO 4) 3F (FAP). The Raman vibrational frequencies decrease upon substitution of Ba 2+ for Sr 2+ or Ca 2+ in the lattice, asymtotically approaching the Raman frequencies for vibrations of the free ion. Splitting of the vibrational Raman frequencies is also observed. The observed splitting is in accord with predictions made by a group theory analysis of the factor group of the unit cell. The effects of the host lattice environment on the magnitude of the Davydov splittings and frequency shifts of crystals within the fluorapatite structure are demonstrated to be inversely proportional to the unit cell volume and proportional to the crystal field in the host crystal.
Published Version
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