Résumé:

We present the results of large-scale computer simulations in order to discuss the structural and dynamic properties of sodium silicate melts with the compositions (Na2O)2(SiO2) (NS2) and (Na2O)20(SiO2) (NS20). We show that, compared to silica (SiO2), these systems exhibit additional intermediate range order on intermediate length scales that stem from the tetrahedral network structure. By means of intermediate-scattering functions, we characterize the dynamics of sodium in the system under consideration. Whereas in NS2 the incoherent scattering functions for Na decay much faster to zero than the coherent ones for Na-Na, in NS20 this different behaviour of the incoherent and coherent functions is not very pronounced. On the other hand, the incoherent functions of the two systems share a very peculiar feature: their long-time decay can be described by a Kohlrausch law with a constant exponent beta for q > q(th) where q(th) is significantly below the location of the main peak in the static structure factor for the Na-Na correlations.

Commentaires: English Article Sp. Iss. SI 665YD