Inelastic neutron scattering on sodium aluminosilicate melts: sodium diffusion and intermediate range order

The interplay of structure and mass transport in sodium aluminosilicate melts at temperatures up to 1600 K has been investigated with inelastic neutron scattering. We compare results of ion dynamics and elastic structure of ternary 3Na2O·Al2O3·12SiO2, 3Na2O·Al2O3·8SiO2, Na2O·Al2O3·6SiO2 and Na2O·Al2O3·4SiO2 with recent results of binary Na2O·3SiO2 and Na2O·2SiO2. Addition of alumina to the binary silicates leads to a decrease in sodium mobility. The prepeak in the elastic structure factor which appears in binary alkali silicates at 0.9 Å−1 and which is interpreted to reflect a network of Na diffusion channels decreases in intensity with increasing alumina content. We find no indication for a prepeak in the Na2O/Al2O3=1 samples. The addition of alumina is apparently disrupting the channel structure found in sodium silicates.