Correlation studies between physical properties and concentration of voids entrenched in V2O5 mixed lead bismuth silicate glass system by means of positron annihilation spectroscopy

Abstract

In this investigation we have estimated the fraction of free volume defects and also their size (to the nanoscale) entrenched in V2O5 doped PbO added Bi2O3–SiO2 glass system (by means of positron annihilation spectroscopy (PAS) studies) with a view to understand the influence of such defects on several physical properties of this glass system. The glasses of the chemical composition viz., 30PbO–5Bi2O3‒ (65- x) SiO2:x V2O5 (0 ≤ x ≤ 0.6, insteps of 0.1) are used in this study. Glasses were prepared by traditional melt quenching technique. PAS studies were perormed using 22Na (0.1 MBq) positron radioactive source. Positron annihilation lifetime is found to be significantly affected by the concentrations of V2O5 dopant. The third component I3 of positrons is found to be feeble in all the glasses. For this reason, initially, we have used a simple two component positron trapping model (ignoring the third component) to calculate annihilation parameters viz., the bulk average positron lifetime (τb), positron trapping rate in defect (κd), fraction of trapped positrons (η), the average lifetime for all the positrons (τavg) and defect-related time (τd). The calculations were repeated with three component positron model. The results of positron annihilation studies have indicated that concentration of free volume nano sized defects, the fraction (fv) of volume defects and their radius (R) are the lowest for the glass V3. Such minimal value of defect concentration is ascribed to dominant existence of vanadium ions in V5+ valence state that involves in glass network forming with VO5 structural units. Whereas, the observed increased value of fv with increase of V2O5 from 0.3 to 0.6 mol% is attributed to growing concentration of vanadyl complexes (VO)2+ that have acted as modifiers. Quantitative information obtained on dependence of concentration of free volume imperfections on V2O5 content in the studied glass is observed to be in good agreement with the inferences drawn from several macroscopic properties that include electrical properties reported earlier.