Effect of Bi2O3 proportion on physical, structural and electrical properties of zinc bismuth phosphate glasses

The variation in physical, structural and electrical properties has been studied as a function of Bi₂O₃ content in 20ZnF₂-(10 + x) Bi₂O₃-(70-x) P₂O₅, 0 ≤ x ≤ 10 mol% glasses, which were prepared by melt quenching technique and characterized by differential thermal analysis (DTA). Colorless samples, which have no absorption peaks, are obtained for 10 and 12 mol% of Bi₂O₃ and the glasses are slowly becoming brownish from 15 to 20 mol% of Bi₂O₃ which exhibit two absorption peaks at ~ 370 nm, ~ 450 nm correspond to Bi° transitions ⁴S_3/2 → ²P_3/2 and ⁴S_3/2 → ²P_1/2 respectively. The decrease in ³P₁ → ¹S₀ transition of Bi³⁺ photo luminescence emission for 18 and 20 mol% of Bi₂O₃ and increase in optical absorption area shows the reduction of Bi³⁺ to Bi°. From FTIR studies it is observed that an addition of Bi₂O₃ decreases the P―O―P covalent bond by forming P―O―Bi bonds due to high polarizing nature of Bi³⁺ ions. Dielectric parameters like ε', tan δ and a.c. conductivity σ_ac are found to increase and activation energy for a.c. conduction is found to decrease with the increase in the concentration of Bi₂O₃. Density of defect energy states is found to increase for higher concentration of Bi₂O₃ and is discussed according to quantum mechanical tunneling (QMT) model.