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Strontium Substitution, Coordination Chemistry and Crystallisation Behaviour of Fluorapatite Glass-Ceramics in the SiO₂–Al₂O₃–P₂O₅–CaO/SrO–CaF₂ System

by Tomas Duminis

Posted: March 3, 2026
Server: Preprints.org
DOI: 10.20944/preprints202603.0260.v1

This study investigates the effect of progressive CaO/SrO substitution on the structure, crystallisation behaviour, and coordination chemistry of fluorapatite-forming glass-ceramics in the SiO₂–Al₂O₃–P₂O₅–CaO/SrO–CaF₂ system. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), ATR-FTIR spectroscopy, ³¹P and ¹⁹F MAS-NMR, and transmission electron microscopy (TEM) were employed to probe both crystallisation and local structural environments. Increasing SrO content reduced the glass transition temperature and suppressed homogenous nucleation, promoting surface-nucleated fluorapatite (Ca5−xSrx(PO4)3F) formation. XRD confirmed fluorapatite as the primary crystalline phase and revealed systematic lattice expansion consistent with partial Sr²⁺ incorporation. ¹⁹F MAS-NMR indicated limited Sr substitution at Ca(II) sites (solid-solution), while ³¹P MAS-NMR demonstrated pronounced phosphorus deshielding, reflecting sensitivity of phosphate tetrahedra to local coordination distortion rather than extensive Sr occupancy. Integrating these findings provides a comprehensive framework for interpreting structural and coordination changes in Sr-fluorapatite glass-ceramics.

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