Abstract
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 νas (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.
Highlights
Modern technological applications have stimulated much importance in the study of optically transparent materials
The objective of this study is to examine the influence of the replacement of oxygen ions by fluorine ions in (50 x)CaO–xCaF2–50P2O5 glasses with x varying from 0 to 20 mol% using Fourier transform infrared (FTIR), Raman and UV–Vis spectroscopy, and mechanical properties by Vickers indentation technique
Since the ionic bonds are non-directional in nature, increasing the CaF2 content will lead to the breakdown of the structural skeleton into a closer packing [15]
Summary
Modern technological applications have stimulated much importance in the study of optically transparent materials. Many investigators introduced fluorine in oxide based glasses and studied the nature of bonding with the network forming cations using X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy [9,10,11,12,13]. They suggested that fluorine ions in glass covalently bond with network forming cations for lower fluorine content and bond with calcium ions for higher fluorine content. There are only a few studies about the effects of fluorine addition on the optical and mechanical properties of phosphate based glasses
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