STRUCTURE AND DYNAMICS OF PHOSPHATE-GLASSES - FROM ULTRAPHOSPHATE TO ORTHOPHOSPHATE COMPOSITION

The short-and intermediate-range order as well as the atomic dynamics in various phosphate glasses were investigated using neutron diffracti on and inelastic scattering. The 3-D network of corner-sharing PO4 tet rahedra in g-P2O5 is highly unstable and hygroscopic. Depolymerization of the network to a chain-like structure and eventually to unconnecte d PO4 units by incorporating alkali, alkali-earth or transition-metal modifiers is clearly evident in the structure factor S(Q) in the Q < 4 Angstrom(-1) region. The dynamic response to such structural changes is equally strong: e.g., the broad P-O stretching band extending to 17 0 meV in g-P2O5 is sharpened and shifted down to similar to 125 meV in the orthophosphate composition. The correlation between the microscop ic structure and physical properties for a series of P-glasses is disc ussed. (C) 1998 Elsevier Science B.V. All rights reserved.