## 3 Results and Discussion
### Thermal Properties
The trends on increase of T\({}_{\rm g}\) according to Z/\(\alpha\) coincide with other studies mentioned above in the current study. In considering the effect of the divalent and trivalent metal cation in M(PO\({}_{3}\))\({}_{\rm n}\), [PERSON] et al. studied the short-range structure and cation bonding in a (1-x)Ca(PO\({}_{3}\))\({}_{2}\)\(\times\)Al(PO\({}_{3}\))\({}_{3}\) glass system. Increasing Al(PO\({}_{3}\))\({}_{3}\) led to the increase in T\({}_{\rm g}\), which can be understood in terms of the replacement of Ca-O bonds by stronger Al-O bonds, i.e., bridging neighboring phosphate chains. In this way, the mobility of the phosphate segments become more restricted, causing an increase in T\({}_{\rm g}\)[18]. [PERSON] et al. reported that an increase of Al(PO\({}_{3}\))\({}_{3}\) in a (1-x)Pb(PO\({}_{3}\))\({}_{2}\)\(\times\)Al(PO\({}_{3}\))\({}_{3}\) glass system leads to the increase of T\({}_{\rm g}\). This phenomenon stems from the fact that Al atoms established stronger, more covalent bonds with nonbridging oxygen. Crosslinking of phosphate chains through Al-O-Al bridges restricts the mobility of these groups, increasing the T\({}_{\rm g}\) of the glass [16]. Based on those references, the divalent (M = Mg) and trivalent (M = Al) metal cations cause structural changes, leading to different thermal properties. As a result, the effect of Al-O bonds or crosslinking of phosphate chains through Al-O-Al bridges by Al(PO\({}_{3}\))\({}_{3}\) was more dominant than that of Mg(PO\({}_{3}\))\({}_{2}\), causing higher T\({}_{\rm g}\) and T\({}_{\rm x}\) than that of Mg(PO\({}_{3}\))\({}_{2}\) in the (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{\rm n}\) (mol%) glass system. Thermal stability (\(\Delta\)T) is frequently characterized by the difference between T\({}_{\rm g}\) and T\({}_{\rm x}\), \(\Delta\)T = T\({}_{\rm x}-\) T\({}_{\rm g}\). It has been well known that the higher the thermal stability for a glass composition, the higher the crystallization resistance during heat treatment [19]. Figure 4 shows the variation of quantitative values of \(\Delta\)T with respect to xM(PO\({}_{3}\))\({}_{\rm n}\) concentration in a (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)\(\times\)M(PO\({}_{3}\))\({}_{\rm n}\) glass system (mol%) (where M = Al, Mg, Na, n = 3, 2, 1, respectively mol%). When increasing the concentration of M(PO\({}_{3}\))\({}_{\rm n}\) up to 15 mol% (M = Mg, Al), it was observed that the \(\Delta\)T increased from 30.4 \({}^{\circ}\)C to 93.2 \({}^{\circ}\)C and 112.9 \({}^{\circ}\)C, respectively. However, the \(\Delta\)T remained almost constant regardless of NaPO\({}_{3}\) concentration, incorporated up to15 mol%. Per review on the thermal effect of phosphate content in a glass system, [PERSON] et al. reported that, in a P\({}_{2}\)O\({}_{5}\)-CaO-Na\({}_{2}\)O glass system, network connectivity, chain length, and molar volume increase in structural behavior as P\({}_{2}\)O\({}_{5}\) increases [20]. [PERSON] et al. and [PERSON] et al. suggested that the density of phosphate glasses is also affected by the phosphate chain length [21,22]. As explained above in Figure 3, structural changes and thermal properties are affected according to the ionic status of cation, i.e., monovalent (M = Na), divalent (M = Mg), and trivalent (M = Al) metal ions. The enhanced glass stability is caused by a lower mobility of longer phosphate chains in the glass network, resulting in a higher energy barrier for rearrangement and subsequent crystallization. The effect of Al(PO\({}_{3}\))\({}_{3}\) was stronger than that of Mg(PO\({}_{3}\))\({}_{2}\) on a lower mobility of longer phosphate chains, leading to a higher exhibited \(\Delta\)T in a (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)\(\times\)M(PO\({}_{3}\))\({}_{\rm n}\) (mol%) glass system.