The influence of B2O3 on structure and ionic conductivity of lithium phosphate-niobate glasses

Glasses in the series (100-x)[0.4Li2O-0.2Nb2O5-0.4P2O5]-xB2O3 were prepared with B2O3 content ranging from 0 to 48 mol%. The glass transition temperature (Tg) increases with up to 8 mol% B2O3, peaking at 512 degrees C, then decreases to 490 degrees C at 40 mol% B2O3. Raman spectra at low B2O3 content indicate the presence of NbO6 octahedra. XRD patterns of crystallized samples reveal NbOPO4 formation across the entire composition range. Confrontation of the Raman spectra of glasses and crystalized glasses resulted in the assignment of the broad Raman band at 777-804 cm- 1 to Nb-O-Nb vibrations in the NbO6 octahedra. 11 B MAS NMR shows a transition from BO4 to BO3 units, while 31 P MAS NMR suggests mixed borate-phosphate structures. Using 2D NMR techniques, mixed species were identified in the glass network. Ionic conductivity remained stable up to 16 mol% B2O3 but decreased significantly at higher concentrations due to reduced Li+ ion mobility in the mixed phosphate-borate network.