| Abstrakt: |
Refractive index and density measurements are given for the ternary systemsX M2O :Y Al2O3: (1 -X -Y)GeO2 where M = sodium and rubidium for Na/(Na + Rb) = 0, 0.3, 0.5, 0.7 and 1.0; (1 -X -Y) = 0.7, 0.8 and 0.9 andY/X = 0, 0.3 and 1.0. The values of the molar refractivity,R, are related to the structure of the glass. At low alkali concentrations, the decrease inR with increasingX is related to the closer packing of the network. At high alkali concentrations the changes inR appear to be controlled by the introduction of non-bridging oxygens into the network. Alumina additions to the germania network strongly increaseR and this appears to be related to change in the network packing brought about by the conversion of Ge4+ from octahedral to tetrahedral coordination. |
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