Estimation of concentration of nano-sized voids ingrained in CuO doped lithium sulphophosphate amorphous system using positron annihilation spectroscopy

Abstract

This study is devoted to investigate the effect of Cu ions on the concentration of defect centres like free volume elements (which influence the physical properties of the glasses to a large extent), integrated in exotic lithium magnesium sulphophosphate glasses using positron (e+) annihilation lifetime spectroscopy (PAL) technique. Glasses of a particular composition viz., 20Li2SO4–20MgO–(60-x) P2O5: xCuO (0 ≤x ≤ 1.0 in mol%) were prepared by traditional melt-quenching technique. The analysis of the glass structure by means of spectroscopic studies, indicated that there is a gradual increasing fraction of Cu+ ions with increase of CuO content. The analysis further suggested that Cu2+ ions acted as modifiers in the glass network while Cu+ ions took part network forming position and increased the rigidity of the glass network. Later, positron annihilation decay profiles in the samples were recorded. 22Na isotope (0.1 MBq) was used as the positron source for this study. The obtained decay profiles were resolved in to three components and the corresponding intensity (I) and lifetime (τ) parameters were estimated and their variations with the concentration of CuO were plotted. The plots suggested that among the three intensity components, the third component (even though its contribution to the total intensity is small) exhibited the largest lifetime and further exhibited a decreasing trend with increase of CuO content. Moreover, radius of the cavity (R) and the fraction free volume (fv) entrenched in the glass matrix are found to decrease with increase of CuO concentration. The analysis of results of these studies in combination with the conclusions drawn from dielectric and related studies suggested a gradual decreasing concentration of Oh Cu2+ ions which induce free volume defects by acting as modifiers. Overall analysis of the results of PAL studies suggested increasing content of CuO facilitates the increasing rigidity or increasing corrosion resistance of lithium sulphophosphate glasses.