Effect of MnO addition on chemical durability, glass-crystal transition, thermal, structural, optical, EPR, and color properties of Na2O-CaO-P2O5 ternary glass system

Abstract

This paper investigates the effect of CaO substitution for MnO on the physicochemical properties in 25Na2O-(30-x)CaO-xMnO-45P2O5 (0 ≤ x ≤ 30 mol%) glass system. These materials were elaborated by the conventional melt-quenching technique at 1050 °C. Free-manganese glass is colorless, while the glasses containing manganese are purple. X-ray diffraction (XRD) confirmed the amorphous state of the studied glasses and showed that the annealing of these glasses leads to a mixture of crystalline phases. Replacing Ca-O bonds with more covalent Mn-O ones in the vitreous matrix increased density (ρ) and glass transition temperature (Tg), indicating the strength of the glass network. Infrared and Raman spectroscopies revealed the existence of PO3, PO2 and PO4 units with P-O-P linkages in the glassy network. EPR spectra exhibited absorptions centered at g ≈ 2, characteristic of isolated Mn2+ ions in distorted octahedral coordination and the optical absorption spectra disclosed bands due to Mn2+ and Mn3+ ions. Decreasing the band gap energy values (Eg) with increasing MnO content agrees with strengthening the vitreous network. Chemical durability results showed the existence of ionic exchanges between distilled water and the studied glasses, and good water resistance is detected for glasses with low Mn content (x = 5 and 10 mol%).