Glass-forming ability and structure of ZnO–MoO3–P2O5 glasses

Glasses in the ternary system ZnO–MoO3–P2O5 were studied. The determined glass-forming region is very large and covers the concentration range from pure P2O5 up to the glass compositions with only 20 mol% P2O5 and 70 mol% MoO3. Structure of these glasses was analyzed in four compositional series containing 50 mol% of P2O5 in the series of (50 − t)ZnO–tMoO3–50P2O5, 10 mol% of ZnO in the series of 10ZnO–yMoO3–(90 − y)P2O5 and 20 mol% MoO3 in the series of zZnO–20MoO3–(80 − z)P2O5. The fourth series contained equimolar ratio of ZnO/P2O5 and its composition was (100 − x)[0.5ZnO–0.5P2O5]–xMoO3. Basic structural units in this ternary system were identified in specific compositional regions using Raman and 31P MAS NMR spectroscopy. By the deconvolution of NMR spectra compositional dependences of Qn units were obtained. The presence of isolated MoO6 octahedra was detected in the glass with 70 mol% P2O5. In the MoO3-rich and ZnO-rich region clustering of MoO6 octahedra was observed, but the formation of Mo–O–Mo bonds was found already in the P2O5-rich glasses containing 60 mol% P2O5. Molybdate structural units are preferentially bonded to non-bridging oxygen atoms of PO4 units and P–O–Mo bonds do not tend to replace P–O–P bonds.