Effect of B2O3 addition on microhardness and structural features of 40Na2O-10BaO-xB2O3-(50-x)P2O5 glass system

Phosphate glasses having composition, 40Na2O-10BaO-xB2O3-(50-x)P2O5, wherex = 0–20 mol% were prepared using conventional melt quench technique. Density of these glasses was measured using Archimedes principle. Microhardness (MH) was measured by Vicker’s indentation technique. Structural studies were carried out using IR spectroscopy and31P and11B MAS NMR. Density was found to vary between 2.62 and 2.77 g/cc. MH was found to increase with the increase in boron content.31P MAS NMR spectra showed the presence of middle Q2 groups and end Q1 and Q0 groups with P-O-B linkages. FTIR studies showed the presence of BO3 and BO4 structural units along with the depolymerization of phosphate chains in conformity with31P MAS NMR.11B NMR spectra showed increase in BO4 structural units with increasing boron content. The increase in MH with B2O3 content is due to the increase of P-O-B linkages and BO4 structural units as observed from MAS NMR studies resulting in a more rigid borophosphate glass networks.