Effect of exchange of Bi+3 b y Nb+5 on the structural and optical properties of some (BBiNb)2 O7 CaO oxide glasses

Series of five samples, named calcium bismuth niobium Borate glasses, were prepared by quenching their melts. The batches of all samples formed according to the chemical formula 60 mol% B2O3 - 20 mol% CaO - 20 mol% Bi2O3 - (20 − x) Nb2O5 mol%, where x = 0, 2.5, 5, 7.5 and 10 1 mol%. XRD, FTIR and UV-vis. Were used to characterize the internal structure of these glasses. Both XRD and FTIR showed the amorphous character for all samples. FTIR showed that all Nb5+ ions occupied some interstitial vacancies, as a glass network modifiers (GNM), while some of Bi3+ ions share in the glass matrix, as a glass network formers (GNF) and some other occupied some other interstitial vacancies (GNM). The BO4 was found to increase by replacing Bi2O3 by Nb2O5, in other word, increase of the non-bridging oxygen atoms. For all samples, UV-vis. exhibited two indirect (γ = 1/2) and direct (γ = 2) electronic transitions. Both the optical band gap and refractive index for direct transition case were found to have slightly increase as x increase. The density of the studied samples was found to be inversely proportional to their molar volume.