Nuclear magnetic resonance studies on vanadium phosphate glasses

The structures of a single V2O5, binary CdO-V2O5 and ternary CdO-V2O5-P2O5 glass systems have been investigated by means of V-51 and P-31 MAS-NMR spectroscopy. NMR spectrum of pure V(2)O(5)( )glass has showed that the network structure is made up of VO5 groups, as in crystalline V2O5. This means that only 5-fold coordination of the vanadium atom, V(5), is the predominant type in this glass. Substitution of V2O5 with CdO in the glass network leads to destruction of the layered VO5 structure and as a result VO4 tetrahedral units are formed. Vanadium is located in this situation at V(5) and V(4) sites. The difference between the feature of NMR spectra of the sample containing 30 mol% CdO and the glass of pure V2O5 is considered to be due to formation of both V(4) and V(5). On the other hand, cadmium orthovanadate Cd-3(VO4)(2) building units are the main constituent of CdO rich glass (60 mol% CdO). The local structure of the ternary CdO-P2O5-V2O5 glasses contains three types of vanadium sites, which are pentavalent vanadate units (V5), tetrahedral (V4) and mixed vanadate and phosphate units (V4-O-P4). The latter represents V atoms coordinated with P atoms as the second neighbor (VO4)P. P-31 NMR results have showed that the concentration of nonbridging oxygen atoms (NBOs) is increased in the phosphate network with increasing CdO contents.