Network structure of 0.7SiO2-0.3Na2O glass from neutron and x-ray diffraction and RMC modelling

The structure of 0.7SiO2-0.3Na2O glass was investigated by means of neutron and high-energy x-ray diffraction. The maximum momentum transfer was 35 and 23.5 A-1 for the two experiments. The two datasets were modelled simultaneously by the reverse Monte Carlo simulation technique. By using reasonable constraints it was possible to separate the six partial pair correlation functions. Nearest neighbour distances, coordination numbers and bond angle distributions have been revealed. It was found that 63% of the O atoms are in the bridging position. The Na-O distance is 2.29 A and the coordination number is 2.5. The Na-Na nearest neighbour distance is 2.6 A, a value significantly smaller than previously reported. Neighbouring sodium ions tend to be located at the same oxygen atom. The average Si-O ring size is 7.6