| Abstrakt: |
Unconventional binary glasses in the system Na2O–Bi2O3have prepared by a conventional pressquenching technique. Xray diffraction XRD, scanning electron microscopy SEM, differential scanning calorimeter DSC, infrared IR spectra, density ρ and, molar volume Vm and dc conductivity σ of these glasses were reported. The overall features of XRD curves confirm the amorphous nature of the present glasses. SEM investigation shows a surface without any microstructure, which is a characteristic of the amorphous phase. Systematic variation of the glass transition temperature Tg, density and IR spectra observed in these glasses indicates significant structural change with composition. Their variation with the composition has been explained by taking into consideration the structure of these glasses. From IR spectra, we conclude the presence of BiO3pyramidal and BiO6octahedral units in the glass structure. From the density ρ and molar volume Vm, the BiO6octahedral units are transformed into BiO3pyramidal units because Na1are introduced within the network of the glass as a modifier and consequently change the structural units into a more open structure. Tgwas observed to decrease with an increase in Na2O content and to lie between 330 °C and 366 °C. The dc conductivity has been explained in terms of the structure of bismuthate glasses. At lower compositions of Na2O, the small variation in conductivity and activation energy has been attributed to the occupancy of Naions at the interstices of BiO6octahedra, acting as a charge compensator, while at higher concentrations of Na2O, the conductivity increases rapidly due to the formation of weak nonbridging oxygen NBO sodium ionic bond. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim |
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