SHORT-RANGE ORDER OF SODIUM-ZINC, SODIUM-COPPER, AND SODIUM-NICKEL PYROPHOSPHATE GLASSES BY DIFFRACTOMETRIC AND SPECTROSCOPIC TECHNIQUES

Short-range order has been investigated in three glasses with composit ion 0.30MeO . 0.35Na(2)O . 0.35P(2)O(5) (Me = Ni, Zn, Cu), which are c omposed of small, ionic units. X-ray diffraction has been used to stud y the cation coordination; average coordination numbers turned out to be about 6 for Ni2+, 5 for Cu2+, and 4.5 for Zn2+. More detailed infor mation has been obtained for Ni2+ through neutron diffraction with iso topic substitution and for Ni2+ and Cu2+ through analysis of their ele ctronic spectra; distorted octahedral and square-based pyramidal geome tries are suggested respectively for Ni2+ and Cu2+. Anionic speciation has been investigated by LR and Raman spectroscopies; the Zn glass ha s been also examined by P-31 MAS-NMR spectroscopy. All three glasses w ere found to be almost exclusively composed of pyrophosphate units. Th ese observations are in agreement with the Van Water's fully ionic mod ifying oxide model for phosphate glasses.