<span class="word">Strontium <span class="word"><span class="changedDisabled">Substitution, <span class="word"><span class="changedDisabled">Coordination <span class="word"><span class="changedDisabled">Chemistry

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−x​Srx​(PO4​)3​F) 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.