International Journal of Pure and Applied Physics
Open Access
  • Year: 2007
  • Volume: 3
  • Issue: 1

A new concept about the static structure and alkali non-bridging oxygen dependence of the mixed alkali effect in bismuthate glasses

  • Author:
  • Sh. El-Desouki1, E.E. Shaisha1, I. Shaltout1, Hoda A. Mady2
  • Total Page Count: 12
  • Page Number: 10 to 21

1Department of Physics, Faculty of Science, Al-Azhar University, Nasr city11884, Cairo, Egypt.

2Department of Physics, Faculty of Science (Girls), Al-Azhar University Nasr city, Cairo, Egypt.

Abstract

The x-ray measurements for the glass system of composition (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x with x between 0 and 40 in steps of 5 has been carried out by means of x-ray powder diffraction using Mo-Kαradiation over [scattering vector,q between 1 and 16A−1] range. X-ray diffraction has been used to calculate the pair distribution function [PDF], g(r), applying the pair potential analytical method. The partial pair distribution function [PPDF], gij(r), of both the metal non-bridging oxygen M-nboand M-bo (M = K or Li, while M-nboand M-bo refers to the non-bridging and bridging oxygen [nbos] respectively) are also calculated by the same method. Both of g(r) and gij(r) are studied as a function of the molar fraction . The PDF, g(r), and the PPDF, gij(r), of M-nboshows a maximum deviation for these functions χ of 0.5 while it shows an insignifically deviation in the case of M-bo. These results could be compared with those obtained for the activation energies Eσ and ED of the conductivity and diffusion respectively which show a maximum deviation around the same alkali molar fraction. They also could be compared with the results of the conductivity which show a minimum deviation at the same ratio. These results lead to the fact that there is a certain relation between the static structure [g(r)] and the mixed alkali effect (MAE).On the other hand the results show a maximum deviation from linearity in the values of PDF's (at first neighbor distance) as function of in the case of K-nboand Li-nbo (potassium and lithium non-bridging oxygen). On the other hand no deviation is observed in the case of K-bo and Li-bo (the case of bridging oxygen). The discussion of the results shows that the static structure (distribution of atoms) and the alkali non-bridging oxygen concentration are strongly related to the mixed alkali effect (MAE) phenomenon. The results are discussed in comparison to the different MAE theories.