Elucidation of the Structural Role of Fluorine in Potentially Bioactive Glasses by Experimental and Computational Investigation

Glasses belonging to the Na<sub>2</sub>O-CaO-P<sub>2</sub>O<sub>5</sub>−SiO<sub>2</sub> system and modified by CaF<sub>2</sub> substitution for CaO and Na<sub>2</sub>O alternatively, were synthesized and characterized experimentally and computationally. The results of molecular dynamics simulations show that fluorine is almost exclusively bonded to modifier cations (Ca and Na) with coordination number close to 4. A similar mean coordination number value is found in the crystal phases obtained by means of thermal treatment at fixed temperature. Addition of fluorine increases the polymerization of silicate tetrahedra by removing modifiers from the siliceous matrix. No appreciable amount of Si−F bonds are detected.