INFRARED-SPECTRA OF SOME SULFATE-APATITES

The infrared spectra of a series of crystalline sul-fate-apatites of the type AI 3M2II(SO4)3X are presented and discussed. It is demonstrated that the sulfate groups are not greatly distorted in these compounds. Apatites with the general formula M5(r04)3x are widely studied because of their biological, industrial and mineralogical importance. One prominent feature of the apatite structure is the great variety of substitutional possibilities which it offers, leading to compounds of different composition and stoichiometries in which, however, the basic structure is retained. It is known that also the SO42- ion can participate in substitutional processes occuring in the apatite lattice, but only a reduced number of pure sulfate-apatites, of formula AI3M2 II(SO4)3X, are wel1 characterized2.As actually nothing is known about the vibrational behaviour of the sulfate ion in the apatitic lattice, it seems interesting to study the i.r. spectra of the known substances of this type. It is supposed that the compounds can crystallize in 4 5 the P6./m space group or in the related P6. group 9 • This 2-means that in the crystal lattice, the 30 ions must occupy C sites (if the space group is P6,/m) or C sites (if it 8 6 7 i J-is P6) 9 . In both cases, site symmetry analysis predicts the total removal of degeneracies and i.r. inactivities, as 6 7. shown in Table 1 (cf.for example The recorded spectra are, in general, very simple and all the predicted band splittings could not be observed in most of the cases. The measured spectra as well as the proposed band assignments are given in Table 2. © 1979, Taylor & Francis Group, LLC. All rights reserved.