Effect of La2O3 on the structure of lead borate glasses

xLa2O3–30PbO–(70 − x)B2O3 (0 ≤ x ≤ 10 mol%) glasses have been investigated by Fourier transform infrared spectroscopy, and ultrasonics. Deconvolution of infrared spectra reveals a small increase with x in the fraction of four-coordinated boron atoms. These results show that La3+ ions have priority to form BO4 units at the expense of Pb2+ ions. A minimum in the sound velocity, elastic properties and transition temperature of glasses observed at 5 mol% La2O3 is correlated with the change in the packing of glass. Higher rate of increase in density for x ≥ 5 mol% is considered due to an increase in the concentration of PbO4 units.