Understanding how the mixed alkaline-earth effect tunes transition metal oxides-tellurite glasses properties

Mixed alkaline-earth effect (MAEE) on the transition metal oxides (TMO)-tellurite glasses [TMO = MoO3, Nb2O5 and WO3] modified with BaO/MgO mix is analyzed to understand how feasible it is to tune structural and optical properties of a tellurite glass. Changes induced by the three transition metal oxides on the tellurite polyhedral produce some modifications on the cut-off wavelength, optical band gap, Urbach's energy, refractive index and permittivity values where the MAEE manifest itself in different ways. The changes in the glass structural properties are dominated by the TMO type while optical and electrical properties depend mostly on the combination between the TMO and the [BaO/(BaO + MgO)] ratio. Glass transition temperature is discussed in terms of some parameters like number of bonds per unit volume, average stretching force constant, molar volume, oxygen packing density values (OPD) and FTIR spectra. In this work we provide evidence that the behavior attributed to the relationship between structure and electrical or optical properties in pure oxide and even binary systems is not reproduced by multi-component glassy systems. A comparison between traditional and new optical methods confirm allowed direct inter-band electronic transitions in the studied glasses evidencing that the a priori parameter election is not always an accurate procedure.