A New Concept about the Static Structure and Alkali Non-Bridging Oxygen Dependence of the Mixed Alkali Effect in Bismuthate Glasses

El-Desouki, Sh.; Shaisha, E. E.; Shaltout, I.; Mady, Hoda A.
March 2007
International Journal of Pure & Applied Physics;2007, Vol. 3 Issue 1, p10
Academic Journal
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-Karadiation 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 X =Li―Li +K. The PDF, g(r), and the PPDF, gij(r), of M-nboshows a maximum deviation for these functions 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 X =Li―Li +K = c 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-nbo 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.


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