Role of non-bridging oxygen defect in the ionic conductivity and associated oxygen trap centers in lead-borate oxide glass: Effect of structural substitution of PbO for Ag2O and Li2O modifiers

Two series of Lead Borate glass with compositions 25B(2)O(3)-(73.8-x)PbO-xM(2)O-0.6Cr(2)O(3)-0.6SeO(2) (M = Ag and Li) with x = 3, 4.5 and 6 mol% in case Ag2O and 3, 6 and 9 mol% for Li2O are prepared using conventional melt quenching technique. The anomalous behavior observed in the measured hydrostatic density and the calculated molar volume at x = 3.0 mol% are explained on the base of the bridging and non-bridging Oxygen bonds formed as a result of introduction of Ag2O as well as Li2O modifiers in the PbO-B2O3 host network. The irregular trend distinguished in the calculated values of the activation energy of ionic conduction are argued to the work done by modifier ions during its motion through the pathways between two non-bridging Oxygen defects. The relaxation frequency peaks observed in the temperature dependent capacitance-frequency measurements indicated that the incorporation of Ag2O and Li2O in lead-borate network produces a non-bridging Oxygen hole centers (NBOHC) trap defect. This relaxation takes place due to an emission from shallow acceptor NBOHC like defect level with an activation energy <= 52 meV for the investigated compositions.