Synthesis and structural characterization of phosphate-based Nasiglasses Na_3Ca_1-xMn_xTi(PO_4)_3 (0 ≤ x ≤ 1)

Nasiglasses with formula Na₃Ca₁₋ₓMnₓTi(PO₄)₃ (0 ≤ x ≤ 1) were synthesized and structurally characterized by DTA, PXRD, EPR, Raman, and density measurements. The density of these glasses increases while the molar volume remains practically constant when manganese replaces calcium, indicating that manganese ions are located in the interstitial sites of the framework, in good agreement with the small variation of the glass transition temperature, observed between the extreme compositions (∆Tg = 23 °C). Crystallization of the glasses at 650 °C leads to the formation of crystalline phases belonging to the Nasicon family. The structure of these crystalline phases consists of three dimensional framework built of PO₄ tetrahedra sharing corners with AO₆ octahedra (A = Ca/Mn, Ti); Na⁺ ions occupy the interstitial sites. EPR study of glasses shows that Mn²⁺ ions occupy octahedral sites, with predominantly ionic bonding between Mn²⁺ and O⁻² ions. Raman spectroscopy study shows that the glasses contain P₂O₇ and PO₄ groups, and short -Ti-O-Ti-O-Ti- chains. The presence of these chains indicates that the TiO₆ octahedra are linked to each other through corners, unlike in the corresponding crystalline phases where they are connected to each-other via PO₄ tetrahedra. All results obtained for the glassy materials indicate that Mn²⁺ and Ca²⁺ ions act as glass modifiers, unlike in the crystalline compounds where they are part of the framework.