On the dual role of ZnO in zinc-borate glasses

• Effect of ZnO addition into borate glasses has been investigated by combining various characterization tools.
• Optical constants of zinc-borate glass structures have been evaluated by Spectroscopic Ellipsometry technique.
• A systematic study has been performed on the dual role of ZnO and number of NBO's in borate glass structures.

ZnO incorporated borate glass structures have been produced by classical melt-quench technique. The effect of ZnO concentration on the behavior of ZnO in glass network as a modifier or network former has been clearly defined by combining various characterization tools. FT-IR transmittance spectra have been used to study the structure of glass systems. Temperature dependent electrical measurements have been performed to investigate the conduction mechanisms, especially at low temperatures. Activation energies determined by considering classical Arrhenius relation and small polaron hopping mechanism support the comments on the behavior of ZnO in glass network. Optical band gap and Urbach energy values have been calculated using optical measurements. Also, Spectroscopic Ellipsometry technique has been used to determine optical constants (refractive index and extinction coefficient) by Cauchy–Urbach model. Results showed that refractive index of borate glasses can be controlled by the composition of ZnO in the structure. Combining all of the outputs from different characterizations, it has been concluded that the amount of ZnO in borate glass structure has a dramatic effect on the number of non-bridging oxygen atoms that determines the role of ZnO as a modifier/network former. ZnO acted as a network former in samples having more than 5% (weight%) incorporation.