Optical basicity and chemical bonding of Bi2O3 containing glasses

Average single bond strength BM-O in kJ/mol of an averaged metal-oxide ion (M-O) chemical bond has been estimated for Bi2O3-P2O5, Bi2O3-B2O3, Bi2O3-SiO2, Bi2O3-GeO2, and CdO-Bi2O3-B2O3 glasses using single bond strength data for simple oxides. It has been found that a decrease in the BM-O is accompanied by an increase in the refractive index based optical basicity A(n(o)) of the glasses. The glasses with high Bi2O3 contents of about similar to 40-70 mol% possess smaller values of the average single bond strength in the similar to 300-160 kJ/mol range than the glasses with high B2O3, P2O5, SiO2, and GeO2 contents of about similar to 80-90 mol% (similar to 430-300 kJ/mol). It has been assumed that the decrease in the interaction parameter and average single bond strength and the increase in the optical basicity in bismuthate glasses with increasing Bi2O3 content could be connected with the formation of mixed Bi-O-B, Bi-O-P, Bi-O-Si, and Bi-O-Ge along with Bi-O-Bi bonds which leads to the increased ionicity in comparison with more covalent P-O-P, B-O-B, Si-O-Si, and Ge-O-Ge bonds. The number of mixed bonds and Bi-O-Bi bonds increases and the number of P-O-P, B-O-B, Si-O-Si, and Ge-O-Ge bonds decreases with increasing Bi2O3 content. An equation for the calculation of optical basicity of SiO2 in Bi2O3-SiO2 glasses has been also suggested taking into account the contribution of different structural units namely SiO40, SiO4-, SiO42-, SiO43-, and SiO44- groups. (C) 2013 Elsevier B.V. All rights reserved.