Na-relaxation and intermediate range structure in sodium-potassium silicate melts

We report on the investigation of fast alkali-ion transport and its relation to microscopic structure for mixed Na-K silicate melts. Na2O K2O 4SiO2, Na2O K2O 6SiO2, and K2O 3SiO2 are studied by means of quasielastic neutron scattering and the results are discussed in the context of results on Na2O 2SiO2, Na2O 3SiO2, and K2O 2SiO2. The height and position of the prepeak in the elastic structure factor scales with the Na2O:K2O ratio between the binary alkali silicates. The addition of K2O to a binary sodium silicate melt appears to have no influence on the time scales of the Na self-relaxation. The data suggest the presence of two different subnetworks of percolation channels in the static structure for the two different alkali species Na and K.