Structure of lead silicate glasses and its correlation with photoelastic properties

Short-range structures of xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses were studied by neutron diffraction and Reverse Monte Carlo modeling. Si–O atomic pair correlation distributions are symmetrical and show peaks in the range: 1.60–1.64 ± 0.02 A. Si4+ are tetrahedrally co-ordinated with oxygen, whereas the Pb–O and O–O atomic pair correlation distributions are broad and asymmetrical due to the existence of wide range of Pb–O and O–O distances in the glass network. The peak positions in the Pb–O atomic pair correlations shift from 2.60 ± 0.05 to 2.42 ± 0.05 A on increasing PbO concentration from 50 to 65 mol%. Pb2+ exist in PbOx (x = 3, 4, 5 and 6) structural units, and the average Pb–O coordination is constant and is in the range of 4.08 ± 0.11 to 4.14 ± 0.08. The O–Si–O bond angles distributions are broad and asymmetrical with peak values in the range of 91° to 109°, and deviate significantly from the value of 109.5° in the ideal tetrahedral structural units. The short-range structural properties of glasses i.e. the cation-oxygen coordination numbers and bond lengths were used to predict the photoelastic properties of the glasses by the Zwanziger model, and it is concluded that xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses should exhibit the properties of zero-stress birefringence.