STRUCTURE OF A COPPER-SODIUM PHOSPHATE-GLASS BY NEUTRON-SCATTERING WITH ISOTOPIC-SUBSTITUTION

The structure of a sodium copper phosphate glass containing approximately equimolar concentrations of CuO, Na2O and P2O5 (0.3CuO.0.35Na2O.0.35P2O5) was studied. From the total structure factor, the oxygen environment of P and Cu can be established. The first- and second-neighbour environment of Cu can be measured more accurately by taking first differences between the normalised scattering intensities for specimens containing Cu-63 and Cu-65. The first-neighbour shell is found to be narrow with a mean radius of 0.2 nm - almost identical to the value found in similar crystals and with a coordination number of 4.0 (as in the crystal). Further oxygens are observed at about 0.25 nm, suggesting that the shell exhibits Jahn-Teller distortions, again as in the crystal, where two atoms are found at the longer distance. The Cu-Cu distribution has been measured directly using second difference techniques. The Cu-Cu signal is extremely weak - due to the low Cu concentration (about 7%) but a peak near 0.6 nm is observed. This corresponds to the mean distance calculated for a random dispersion of Cu atoms in the glass but the peak is so narrow that the Cu environment is clearly not random. In particular, it is possible that the Cu is 'solvated' by a shell of Na-O polyhedra.