Structural, optical and mechanical properties of ternary CaO–CaF₂–P₂O₅ glasses

The ternary phosphate glass series (50-x)CaO–xCaF₂–50P₂O₅ (x = 0–20 mol%) were synthesized using melt quench technique. Structural, optical and mechanical properties were investigated with increase in CaF₂ content. Using X-ray diffraction (XRD), synthesized glasses were confirmed to be amorphous in nature. Replacement of oxygen ions by fluorine ions increased the values of density. Decrease in refractive index due to the low polarizability of fluorine ions in the glass matrix was observed. In Fourier transform infrared (FTIR) spectra, the slight variation in ${\nu }_{\text{as}}$ (PO₂) band position and intensity could be attributed to replacement of fluorine ions for oxygen ions in phosphate glass structure. These data were well supported by Raman spectra. Optical band gap energy increased from 3.44 eV to 3.64 eV with increase in CaF₂ content, and Urbach energy decreased suggesting that the fluorine ions reduced the tail energy states in the band gap compared to the oxygen ions. Mechanical parameters such as Vickers hardness, fracture toughness and brittleness were evaluated from the Vickers micro indentation measurements. Increase in Vickers hardness, decrease in fracture toughness and increase in brittleness were observed with increase in CaF₂ content.