Mixed network former effects in tellurite glass systems: Structure/property correlations in the system (Na2O)1/3[(2TeO2)x(B2O3)1−x]2/3

Mixed-network former effects upon glass transition temperatures, densities and electrical conductivities have been studied in glasses in the system (Na2O)1/3[(2TeO2)x(B2O3)1 − x]2/3. Mixing of network formers B2O3 and TeO2 has a negative effect on ionic conductivities. Possible structural origins of this behavior have been studied by 11B, 23Na, and 125Te high-resolution and dipolar solid state nuclear magnetic resonance (NMR) techniques, O-1s X-ray photoelectron spectroscopy and Raman spectroscopy. A quantitative structural model has been developed that is consistent with all of the experimental data, and provides a detailed description of network modification processes, interactions and connectivities. All the O-1s XP spectra can be satisfactorily fitted with two line shape components with the parameters of the binary end-member glasses, providing no evidence for the possible formation of B–O–Te linkages. In addition, none of the 125Te and 11B NMR data shows significant proof of such linkages, even though their formation cannot be explicitly excluded. 23Na NMR data indicate a monotonic chemical shift trend consistent with proportional sharing of the network modifier between the two network former species. The experimental data suggest a tendency towards an avoidance of B–O–Te linkages, even though no macroscopic phase separation is observed. Nevertheless, the negative mixed network former effect can be rationalized in terms of compositionally segregated sodium borate and sodium tellurite nano-domains.