## 3 Results and Discussion
### Thermal Properties  
One of the most important characteristics for evaluating the glassy state and thermal properties is glass transition temperature. Figure 3a presents the differential scanning calorimetry (DSC) traces, measured in the range of 25-550 \({}^{\circ}\)C, for the (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{n}\) glass system (mol%) (where M = Al, Mg mol%, n = 3, 2, respectively). The traces were obtained for different metaphosphates at various concentrations. The distinctive temperatures, such as the glass transition temperature (T\({}_{\rm g}\)), crystallization onset temperature (T\({}_{\rm x}\)), and peak crystallization temperature (T\({}_{\rm p}\)), were evaluated from the DSC curves as shown in Figure 3b. The T\({}_{\rm g}\) is obtained by drawing the tangent to the endothermic peak, while the T\({}_{\rm x}\) is taken as the temperature at which heat flow starts to increase from its constant value. We investigated the effect of monovalent (M = Na), divalent (M = Mg), and trivalent (M = Al) metal ions of xM(PO\({}_{3}\))\({}_{n}\) on thermal properties, such as T\({}_{\rm g}\), T\({}_{\rm x}\), and T\({}_{\rm p}\), as shown in Figure 3b. When the concentration of xM(PO\({}_{3}\))\({}_{n}\) was increased up to 15 mol% (M = Mg, Al), it was observed that the T\({}_{\rm g}\) increased from 263 \({}^{\circ}\)C to 289 \({}^{\circ}\)C and 302 \({}^{\circ}\)C, respectively. However, the T\({}_{\rm g}\) of the 55V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xNaPO\({}_{3}\) glass system was not considerably changed with respect to NaPO\({}_{3}\) concentration. The T\({}_{\rm x}\) increased linearly from 293 \({}^{\circ}\)C to 383 \({}^{\circ}\)C and 405 \({}^{\circ}\)C, respectively, with an increase in Mg(PO\({}_{3}\))\({}_{2}\) and Al(PO\({}_{3}\))\({}_{3}\) contents up to 15 mol%. The increased NaPO\({}_{3}\) content up to 15 mol% led to the slight increase of T\({}_{\rm x}\) from 263 \({}^{\circ}\)C to 274 \({}^{\circ}\)C. In brief summary, this concludes that the T\({}_{\rm g}\) and T\({}_{\rm x}\) increased in the order of Al(PO\({}_{3}\))\({}_{3}\), Mg(PO\({}_{3}\))\({}_{2}\), and NaPO\({}_{3}\) added in the (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{n}\) (mol%) glass system. This behavior can be related to the bond strength of the glass network which can be explained in terms of the cation field strength (which is the charge divided by the square of the cation oxygen distance). In other words, thermal properties of glass could be influenced by various metaphosphate species, because M(PO\({}_{3}\))\({}_{n}\) with different metal cations showed different cation field strength depending on their charge, as shown in Table 2[17,18]. It can  
Figure 3: Effect of M(PO\({}_{3}\))\({}_{n}\) concentration on thermal properties in V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{n}\) (where M = Al, Mg, Na mol%, n = 3, 2, 1, respectively) glass system. (a) DSC curves, (b) glass transition temperature (T\({}_{\rm g}\)), crystallization onset temperature (T\({}_{\rm x}\)) and peak crystallization temperature (T\({}_{\rm p}\)). be seen that the Z/\(\alpha\) increases in the order of cation, i.e., monovalent (M = Na), divalent (M = Mg), and trivalent (M = Al) metal ions. The reason behind trivalent Al(PO\({}_{3}\))\({}_{3}\) with a high Z/\(\alpha\) having the highest T\({}_{\rm g}\) and T\({}_{\rm x}\) was analyzed. As plotted in Figure 3b, it was observed that the degree of increase in T\({}_{\rm g}\), T\({}_{\rm x}\), and T\({}_{\rm p}\) is closely related to the Z/\(\alpha\) of cation, in order, in the present glass system. [PERSON] et al. reported that the increase in T\({}_{\rm g}\) with Z/\(\alpha\) was described according to different cation in alkali and alkaline earth phosphate glasses. It might then be due to the rise of the glass network strength and connectivity [15].