Influence of nickel ion concentration on the free volume defects entrenched in an alkali sulphophosphate glass system by means of positron annihilation characterization technique

•In this study concentration of defects in Li2SO4−MgO−P2O5: NiO glass system is estimated.•PAL technique with 22Na positron source (100 kBq) is used for this study.•Glass doped with 0.8 mol% of NiO found to contain maximal concentration of defects.•Higher concentration of defects is ascribed to maximal presence of Oh Ni ions in this glass.•Obtained info is found to be in concurrent with inferences drawn by other studies. In this study we have evaluated the concentration of defect centers like voids, their size (up to nanoscale) and the fraction of free volume space integrated in Li2SO4−MgO−P2O5:NiO glass system as a function of NiO content. Positron annihilation lifetime (PAL) technique with 22Na positron source of radio activity 100 kBq is used for this study. The size, shape and the concentration of entrenched defects in the glass matrix are predicted to influence profoundly the physical properties of the glass. Cavity radius (R) and the entrenched free volume fraction (fv) are found to be the maximal in the sample doped with 0.8 mol% of NiO. This observation suggested that Ni2+ ions predominantly occupied octahedral positions (acted as modifiers along with SO42– ions) and induced large concentration of structural defects. The obtained information is found to be in concurrent with inferences drawn from dielectrics and spectroscopic studies of these glasses reported earlier.