Role of Mixed Valence Effect and Orbital Hybridization on Molar Volume of Heavy Metal Glass for Ionic Conduction Pathways Augmentation

摘要

Ionic conductivity of glasses can be engineered by understanding the chemical bonding properties and their effect especially on the glass molar volume. Thus, a series of heavy lead borate glass of the composition 0.25B₂O₃–0.75PbO is prepared by the melt quenching technique. The mixed valence effect and orbital hybridization of 3d-transition metal oxide and 4p-chalcogen combination are used through the co-substitution of Cr₂O₃ and SeO₂ by B₂O₃ to open up the glass network and to increase the glass molar volume. It provides weaker anionic tetrahedral unit linkages instead of strong oxygen linkages of triagonal units. Moreover, a gradual conversion of chromium ions from Cr⁶⁺ state to Cr³⁺ state exists where the Cr³⁺ ion is acting as a modifier to break up the glass local symmetry introducing additional coordinated defects. Among the different negative sites, the existence of nonbridging oxygen bonds and orbital hybridization or pπ-dπ overlaps the molar volume increases and the glass network becomes more open. Thus, it would provide wide pathways for ions like Li⁺ to be more easily mobile in the glass matrix. Chemical bond approach is used to explain the obtained results.