Investigation of Novel Low Melting Phosphate Glasses Inside the Na2O–K2O–ZnO–P2O5 System

Phosphate glasses containing different concentrations of zinc oxide inside the (1 − x)(NaPO3–KPO3)–xZnO system (0 ≤ x ≤ 50 mol%) have been prepared using the conventional melt quenching technique. The prepared glasses were transparent, bubble-free and colourless. Their density, molar volume, glass transition temperature, and structural properties using infrared and Raman spectroscopies are investigated. As the content of ZnO increases, the density increases while the molar volume decreases. The composition dependence of Tg shows a minimum for the glass (x = 20 mol%). Structural approach realized by IR and Raman spectroscopies reveals that zinc ions occupy different sites in the glassy-network, mainly modifier sites and middle phosphate network in low-zinc and high-zinc glasses, respectively. The introduction of ZnO in the network induces some structural rearrangements through the conversion of metaphosphate structural units to pyrophosphate ones. It is also highlighted that the presence of ZnO in the glassy matrix allows the transformation of some P–O–P and P=O bonds to P–O–Zn linkages. From the UV–Visible absorption studies, the values of the optical band gap, Eg, and Urbach energy, ΔE, were evaluated. The optical band gap is found to depend on the glasses composition. Eg and ΔE show a minimum and a maximum respectively, for the glass (x = 20 mol%).