ROLE OF THE ZINC CATION IN THE STRUCTURAL ORDERING IN SODIUM ZINC SILICATES

The evolution of the 'boson peak' contour in low frequency Raman spect ra of a few Na2O-ZnO-SiO2 compositions was observed under subsequent s ubstitution of Na2O for ZnO. Frequency shift of this mid-order sensiti ve feature shows a decrease of the glass correlation radius with an in crease in zinc oxide concentration (while keeping the SiO2 content con stant). In structural terms the correlation sphere size reflects the d imension of the glass cell unit. In terms of physical properties, the effect is connected with the densification of the glass resulting from a change of modifying ions. Restriction of the molecular mobility of tightened structural elements produces unfavourable conditions for mid -range ordering.