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 have been carried out by means of X-ray powder diffraction using Mo--K_α radiation over [scattering vector, q between 1 and 16~A^-1] range. X-ray diffraction has been used to calculate the pair distribution function g(r) applying the pair potential analytical method. Both the partial pair distribution function gij(r) and the partial pair distribution function [PDF] of the metal non-bridging oxygen g_ij(r) M-nbo are also calculated by the same method. The composition dependence of these functions shows a maximum deviation around the alkali mole fraction (Li/Li+K) of 0.5. These results could be compared with those obtained for the activation energies E_σ and E_D of conductivity and diffusion respectively which show a maximum deviation around the same alkali mole fraction. They also could be compared with the results on conductivity which show a minimum deviation at the same ratio. These results lead to the conclusion 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 in the values of PDF's (at first neighbor distance) as function of Li/Li+K in the case of K-nbo and Li-nbo (potassium and lithium non-bridging oxygen). Whereas 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 with various MAE theories.

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