Characterisation of the structure of binary calcium ultraphosphate glasses by infrared and Raman spectroscopy

ISSN： 0031-9090

Source： Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B, Vol.39, Iss.2, 1998-04, pp. : 108-117

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Abstract

A series of calcium phosphate glasses xCaO.(1–x) P₂O₅, with 0≤x≤0·5 and the crystalline compounds of this composition range are investigated by infrared and Raman spectroscopy. The change of the spectra is characterised by the transformation of the threefold connected PO₄ tetrahedra to double connected PO₄ tetrahedra with increasing CaO content. The bands are assigned on the basis of the interpretation of the vibrational spectra of the crystalline compounds. The evaluation of the spectra of the glasses supported by the application of multivariate statistics gave that the samples with x=0, 0·2, 0·33 and 0·5 have special spectral features, that means special structural features. Even the measured density composition curve of the glasses shows peculiarities for the glasses with x=0·2 and 0·33. The results of the analysis of the spectra are compared with the results of x-ray diffraction on the same glasses. The derived model of the structure of the calcium ultraphosphate glasses is based on substructures defined by the number, type and interconnection of several PO⁴ tetrahedra and CaO_n polyhedra. There are four different substructures because the glasses with x=0, 0·2, 0·33 and 0·5 consist of a single substructure and the glasses with other compositions are nonideal mixtures of the two neighboured substructures.