Group optical basicity and single bond strength of lead borate glasses

Equation providing the calculation of the theoretical optical basicity Λ_th(1) of PbO-B₂O₃ glasses is suggested taking into account the contribution of the mole fraction and the group basicity of different structural units, namely BO₃ and BO₄ groups. It is found that in case of PbO-B₂O₃ glasses the curves of the refractive index based optical basicity Λ(n0) and the theoretical optical basicity Λ_th(1) as a function of PbO content follow a similar trend changing their slope at about 50 mol. % PbO. An equation is proposed to calculate the average single bond strength B_M-O of PbO containing borate glasses taking into account the mole fractions of PbO₃, PbO₄, PbO₆, BO₃ and BO₄ groups. It is established that both equations give the possibility for more precisely estimation of the theoretical optical basicity and the single bond strength of the glasses. It is found that the single bond strength of PbO-B₂O₃ glasses decreases with increasing PbO content. The observed increase of the optical basicity with decreasing single bond strength of lead borate glasses is discussed with increase the number of Pb-O-B and Pb-O-Pb bonds containing oxide ions with increased polarizability. Keywords: borate glasses, electronic polarizability, optical basicity, average single bond strength