Physical properties of unconventional binary sodium bismuthate glasses

Abstract

AbstractUnconventional binary glasses in the system Na2O–Bi2O3 have prepared by a conventional press‐quenching technique. X‐ray 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 BiO3 pyramidal and BiO6 octahedral units in the glass structure. From the density (ρ) and molar volume (Vm), the BiO6 octahedral units are transformed into BiO3 pyramidal units because Na+1 are introduced within the network of the glass as a modifier and consequently change the structural units into a more open structure. Tg was 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 Na+ ions at the interstices of BiO6 octahedra, 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 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)