THE EFFECT OF COMPOSITION IN LEAD GALLATE GLASSES - A STRUCTURAL STUDY

Neutron diffraction has been performed on two samples from the PbO-Ga2 O3 glass-forming system with 67 mol% PbO and 80 mol% PbO. The results show that the structure involves a network based on GaO4 tetrahedra, T he PbO has an essential oxygen-providing role in the formation of the network. The high lead limit of the glass-forming range, similar to 83 mol% PbO, is shown to correspond to the connectivity of the Ga-O netw ork going to zero, The abrupt change in some physical properties at si milar to 75 mol% PbO is shown to correspond to the initial formation o f GaO4 tetrahedra with a connectivity of zero, The low lead limit of t he glass-forming range is higher than the theoretical equimolar limit due to the constraining effect of the Pb-O coordination shell on the b ond and torsion angles of the Ga-O network.