Effect of modifier on the silver based fast ion conducting glasses for solid state batteries

Fast ion conducting (FIC) glasses of composition 60%AgI-[MAg₂O-F{(F1)B₂O₃-(F2)TeO₂}] (SBT2);where M/F = 0–2 in steps of 0.25 for a fixed values of former [F={(F₁ = 0.4)+(F₂ = 0.6)}]are prepared by melt quenching technique. X-ray diffraction and differential scanning calorimetry studies were carried out understand some structural aspects of the glasses. With increasing the value of M/F ratio upto 1.50 (SBT2-6), the samples exhibited amorphous nature and for further increase of this ratio, crystallinity could be visualized. The electrical properties of these glasses are investigated by impedance spectroscopy in the frequency range 1 kHz–3 MHz and also DC conductivity in the temperature range 303–423 K. The conductivity is observed to increase while the activation energy exhibited decreasing trend with increase of modifier (Ag₂O) concentration upto M/F = 1.50. The electrical properties of these glass systems were described as a parallel RC circuit in which R represents the bulk resistance (R_b) and C represents the bulk capacitance (C_b) of the sample. The AC conductivity is also found to increase upto M/F = 1.50. The glasses exhibited high ionic conductivity and near unity ionic transport number, such observation confirms the studied materials are superionic conductors. Overall analysis of the results further indicated the SBT2-6 sample (which is amorphous in nature) that exhibited the highest conductivity with lowest activation energy and high ionic transport number is better useful as solid electrolyte (SE) in solid state batteries (SSBs).