Structural and electrical properties of ZnF2–Bi2O3–GeO2 glasses doped with CoO

Transparent glasses 20ZnF2–40Bi2O3–(40 − x)GeO2:xCoO; 0 ⩽ x ⩽ 1 wt% are prepared by melt quenching technique. The amorphous nature of the 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, conductivity σac over a wide range of frequency and temperature as well as dielectric breakdown strength at room temperature) of these samples have been carried out. Optical absorption data has revealed that the bismuth radicals, observed in pure sample C0, are combined with cobalt ions with increase in concentration of CoO. Further, Co2+ and Co3+ ions occupy octahedral positions at larger dopant concentrations of CoO. From FTIR and Raman studies the coordination of germanium is changed from GeO4 to GeO6 with increase in the concentration of CoO. Dielectric parameters such as dielectric constant ε′, loss tan δ, a.c. conductivity σac are increased and activation energy for a.c. conduction is decreased and hence opens the glass network with the increase of divalent cobalt ion concentration; which is also confirmed by decrease in glass transition temperature (Tg) and band gap energy (Eg). Density of defect energy states (EF) is explained with quantum mechanical tunneling (QMT) model.