Free volume estimation in Au and Ag mixed sodium antimonate glass ceramics by means of positron annihilation

Abstract

Earlier, we have reported the results of quantitative studies on structural and a variety of physical properties (that include non-linear optical, piezo-optical and electrical characteristics) of Na2O-Sb2O3:Ag2O/Au2O3 glass ceramics. In continuation of these studies, this part of the investigation is devoted to estimate the concentration of the defects and the free volume space (up to the nano scale) entrenched in the titled glass ceramics (as functions of the concentrations of dopant noble metal ions) by means of positron annihilation lifetime spectroscopy (PAS) technique. Such defects are predicted to have tremendous influence on above mentioned physical properties of these glass ceramics. Glasses of the composition (40-x) Na2O–60 Sb2O3: xAg2O/Au2O3 (x = 0.025–0.15 mol% for Ag2O glasses and x = 0.025–0.1 mol% for Au2O3 glasses) were prepared by melt quenching and subsequent heat-treatment for prolonged times. PAS studies were performed using 22Na positron source of strength 0.1 MBq. The results of these studies indicated significant influence of the concentrations Ag2O and Au2O3 on positron annihilation lifetime in the samples. In both the series of the samples, the third component of intensity, I3 (among the three components) is observed to be the longest-lived component. Further, for Ag2O doped glass ceramics, the value of I3 is found to be the maximal, whereas the life time component τ3, concentration of nano sized free volume defects and their volume fraction (fv), cavity radius (R) are found to be minimal for the samples doped with 0.1 mol% Ag2O and for the Au2O3 doped glass ceramics, these parameters have exhibited continuous decreasing trend with increase of Au2O3 concentration. Such decrease of defect concentration is attributed to the increasing degree of participation of antimony ions in the glass network forming with Sb(V)O4 structural units. Overall, information obtained regarding the dependence of free volume defect concentration on the contents of dopants is well in accordance with conclusions drawn from various macroscopic properties of these materials presented in our earlier reports.