Structural changes in the ZnF2–Bi2O3–GeO2 glass system doped with Fe2O3 by spectroscopic and dielectric investigations

Transparent glasses 20ZnF2–40Bi2O3–(40−x)GeO2: xFe2O3; 0≤x≤2.5 wt% are prepared by melt quenching technique. The amorphous nature of the glass samples is characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). Spectroscopic studies like optical absorption, FTIR, Raman and dielectric parameters (ε′, loss(tan δ) and σac over a wide range of frequency and temperature) of these samples have been carried out. Optical absorption data has revealed that the bismuth radicals, observed in pure sample F0, are decreased with increase in concentration of Fe2O3. The optical absorption and ESR studies indicate Fe2+ and Fe3+ ions occupy octahedral positions at higher dopant concentrations of Fe2O3. From FTIR and Raman studies, the coordination of germanium is changed from GeO4 to GeO6 with increase in the concentration of Fe2O3. Dielectric parameters such as dielectric constant ε′, loss tan δ, a.c. conductivity σac are found to increase and activation energy for a.c. conduction is decreased, hence depolymerise the glass network with increase of divalent iron ion concentration; which is also confirmed by band gap energy (Eg). Density of defect energy states N(EF) is explained with quantum mechanical tunnelling (QMT) model.

► Structural changes in zinc-germanate glasses doped with Fe2O3 are investigated.
► Bismuth radicals are observed at lower concentrations of Fe2O3.
► GeO4 structural units are converted in to GeO6 with increase in mol % of Fe2O3.
► Fe2+ ions and GeO6 structural units are liable for the decrease in the rigidity of network.
► At higher mol % of Fe2O3 the conductivity of the network is observed to increase..