## 3 Results and Discussion
### Structural Properties  
Vibrational spectroscopy, namely Raman spectroscopy in this work, can supply useful information about the structure of non-crystalline materials. In comparison with IR spectroscopy, Raman spectroscopy is more sensitive to vibrations of bonds with a high covalence, which is advantageous for the study of changes in the structure of the phosphate backbone (P-O bonds) and the vibrations of V-O bonds in which a higher content of covalence (higher polarizability) is also assumed, contrary to the higher ionicity of Zn-O bonds. Figure 6 shows the Raman spectra of a 55V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-15M(PO\({}_{3}\))\({}_{n}\) (where M = Al, Mg, Na, n = 3, 2, 1, respectively, mol%) glass system modified with M(PO\({}_{3}\))\({}_{n}\) concentration up to 15 mol%. As is seen from the spectra, all the studied glasses showed the characteristic vibration bands of vanadium and phosphate. The peak position and assignment of the vibrational bands observed at around 275, 491, 706, 991, 1120, and 1326 cm\({}^{-1}\) are shown in Table 3. The distinctive bands related to the V\({}_{2}\)O\({}_{5}\) are observed at 291, 399, 665, 799, and 1154 cm\({}^{-1}\) which are assigned as shown in Table 3. The short-range order of phosphate glasses has been commonly described by the concepts of four different phosphate structural units derived from PO\({}_{4}\) tetrahedra, labeled as Q\({}^{n}\), where the superscript n = 0, 1, 2, and 3 denotes the number of bridging oxygen per tetrahedron [29]. Q\({}^{0}\) represents the orthophosphate groups, Q\({}^{1}\) indicates the terminal units of chains or pyrophosphate groups (Q\({}^{1}\)-Q\({}^{1}\)), Q\({}^{2}\) corresponds to metaphosphate groups, and Q\({}^{3}\) attributes to ultraphosphate groups. As shown in Figure 6, it is clear that the intensity and bandwidth of the Raman bands increased with the substitution of different metaphosphates, as compared to that of base VZBB glass. It is worth mentioning that the intensity and bandwidth of the distinctive bands observed at around 275, 706, and 991 cm\({}^{-1}\) significantly increased when Al(PO\({}_{3}\))\({}_{3}\) metaphosphate substituted for V\({}_{2}\)O\({}_{5}\) due to the formation of strong V-O-Al coupling and a broadening and merging of bands. The decrease in broadening of the bands is clearly observed, with decreasing charge and covalence of the ions from Al\({}^{3+}\) through Mg\({}^{2+}\) to Na\({}^{+}\). Furthermore, Raman spectra also showed the shift of the P-O-P band to lower energies, with decreasing charge and covalence of the ions from Al\({}^{3+}\) through Mg\({}^{2+}\) to Na\({}^{+}\). This indicates that the Al bands merge together with the phosphate network deformation bands due to coupling of Al-O-P. Other bands also show some degree of merging. This behavior is validated from the XPS studies in a M(PO\({}_{3}\))\({}_{n}\) modified (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{n}\) (mol%) (where M = Al, Mg, Na, n = 3, 2, 1, respectively, mol%) glass system. Structural analysis via X-ray photoelectron spectroscopy (XPS) was carried out to identify the correlation between the change in thermal properties and the structural change depending on M(PO\({}_{3}\))\({}_{n}\) in a (70-x)V\({}_{2}\)O\({}_{5}\)-5 ZnO-22 BaO-3B\({}_{2}\)O\({}_{3}\)-xM(PO\({}_{3}\))\({}_{n}\) (mol%) (whereM = Al, Mg, n = 3, 2, respectively, mol%) glass system. A nonlinear, least-squares algorithm was employed to determine the best fit to the O 1s spectra, with three Gaussian-Lorentzian curves in order to distinguish various oxygen bonding sites (such as BO and NBO). The fraction (relative abundance) of various oxygen bonding sites was determined from the respective area ratios obtained from optimized fits. Figure 7 shows the high-resolution XPS spectra along with their deconvoluted curves for the O 1s core level for AP15 and MP15.