About the Symmetry Lowering of Some Apatites as Evidenced by Their Infrared Spectrometric Study

Abstract

The effect of substitution of channel ions in apatites on the structures was studied by x-ray diffraction and IR spectroscopy. The compds. Ca10(PO4)6CO3, Ca10(PO4)6O, Ca10(PO4)6O2, and Ca10(PO4)6S are isomorphous with fluoropatite and belong to space group P63/m according to diffraction data. Ca10(PO4)6(OH)2 belongs to the above space group but Ca10(PO4)6CO3, Ca10(PO4)6O, Ca10(PO4)6O2, and Ca10(PO4)6S do not according to IR data. This is due to suppression of symmetry elements in the unit cell of the crystal which then simulates P63/m symmetry by a random arrangement of bivalent ions and vacancies along the channels. Partial hydrolysis of Ca10(PO4)6Cl2 indicates symmetry lowering in the IR data. Thus, IR spectroscopy appears to be a more useful tool for studying apatite structures than x-ray diffraction alone. [on SciFinder (R)]