Electronic and optical properties of Na₂O doped P₂O₅-TeO_2⁻ CoO-ZnO glasses

Abstract

The phospho-tellurite glasses, (P2O5)0.25-(TeO2)0.5-x-(CoO)0.1-(ZnO)0.15-(Na2O)x ; x = 0.15, 0.20, 0.25, 0.30 and 0.35 were prepared by melt quenching and their non-crystalline nature confirmed through XRD. Density is found decreased and molar volume increased with increase of Na2O concentration and they behaved opposite to each other. The physical parameters such as transition metal ion density, mean distance between TMIs, small polaron radius, oxygen packing density and field strength were estimated. DC conductivity was measured by following two probe method in the temperature range 303K – 633K. High temperature conductivity is explained by Mott’s small polaron hopping (SPH) model and low temperature conductivity by Mott’s VRH model. Both conductivity and activation energy are found to be increasing with Na2O content. Density of states at Fermi level are found to be of the order of 1021 to 1024 eV−1 cm−3. UV-Vis spectra were recorded for the wavelength range 200-800 nm. Optical band gap (direct and indirect) except for x=0.20 is found increased, urbach energy and refractive indexes are found decreased with Na2O concentration. Various optical parameters such as molar polarizibility, metallization criterion, reflection loss, electronic polarizability, optical transmission coefficient, dielectric constant and optical dielectric constant have been determined.