Münster 1999 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
DF: Dielektrische Festkörper
DF 7: Gläser
DF 7.2: Vortrag
Donnerstag, 25. März 1999, 15:20–15:40, R2
Mixed oxide effect in metaphosphate glasses — •G. Walter1, U. Hoppe1, R. Kranold1, A. Barz2, and D. Stachel2 — 1Department of Physics, Rostock University, D-18051 Rostock — 2Otto Schott Institute, Friedrich Schiller University Jena, D-07743 Jena
The gradual metal oxide substitution for alkali and alkaline earth oxide, respectively, in metaphosphate glasses has been studied by X-ray diffraction. The intermediate range ordering of the two-connected PO4 units and the MeOn polyhedra in metaphosphate glasses was shown to depend on the special network modifier cations being effective. Information on such structural processes can be extracted from the X-ray scattering total structure factor, S(s), i.e. from its main peak (around sm ≅ 20 nm−1), the prepeak at s1<sm and the zero angle scattering intensity, S(0). Further knowledge is gained by structural simulations using Reverse Monte Carlo technique.
Properties like mass density and glass transition temperature measured for the glasses studied do not give any indication of the existence of a mixed oxide effect. However, for barium-sodium metaphosphate glasses it was observed [Bunker, B. C. et al., J. Non-Cryst. Solids 64 (1984) 291] that the durability does not alter continuously with mixing ratio. For these glasses, the intermediate range order parameter, S(0), which represents a measure for the heterogeneity of glasses, is non-additive with respect to the participating binary systems. The compositional dependence of S(0) is consistent with the formation of a quasi-periodicity in electron density whose signature is the prepeak in the total structure factors. The features of the quasi-periodic superstructure in the mixed glasses were found to be determined by the specifics of packing of the PO4 chains and the MeOn polyhedra in the binary systems involved.
This work was supported by the BMBF (Grant 03-KR5ROK-9).