Impact of substitution of B2O3 by Bi2O3 on the structural changes and associated oxygen defect centers in B2O3-TeO2 glass

Abstract

Bulk samples of compositions x(Bi2O3)-(0.5-x)(B2O3)-0.5(TeO2) with x = 0.05, 0.1, 0.2, 0.3 and 0.4 are prepared using melt quenching technique The IR absorbance revealed that at x = 0.05 the network is mainly constituted by [BiO3] and [BiO5], [BO3] trigonal pyramid and [BO4] tetrahedron, [TeO4] trigonal bipyramidal and [TeO3] trigonal pyramid structural units. Increasing Bi2O3 content over 0.05 transforms [BO4] to [BO3], [TeO3] to [TeO4] and [BiO3] into [BiO5]. The calculated ratio of BO4 in the structural network showed a decrease against the increase in Bi2O3which is explained according to the density of bridging and non-bridging oxygen defects. Temperature dependent capacitance-frequency measurements showed relaxation peaks which argued to the non-bridging Oxygen hole centers (NBOHC) trap defects. The emission rate of these NBOHC defects appeared that its energy states are located as deep levels with respect to the conduction band edge.