Evaluation of chemical durability, thermal properties and structure characteristics of Nb-Sr-phosphate glasses by Raman and NMR spectroscopy

Thermal properties, water durability and structure of Nb2O5-SrO-P2O5 glasses containing 0-25 mol% Nb2O5 and 35-60 mol% SrO were explored aiming to develop high refractive index optical glasses. Structure studied using Raman and NMR spectra reveals that by increasing Nb2O5 content, niobium plays the role as intermediate. Nb5+ tends to break P-O-P and O-P-O bonds forming [NbO6] structure. Thus fractions of Q3 and Q2 decrease, while Q1 fraction increases. Furthermore the Q0 fraction replaces the lessened Q3 fraction. As P2O5 content is reduced to 30 mol%, partial [NbO6]octa turns into [NbO4]tetra and partial (Nb-O)short-octa becomes (Nb-O)short-tetra bond to stabilize the glass structure. Glass-transition and softening-temperatures of the glasses increase by increasing SrO and Nb2O5 contents. Thermal expansion coefficient increases by increasing SrO while decreases with Nb2O5 content. Water durability is enhanced as increasing Nb2O5 and SrO contents. Properties of the glasses correlate well with the worked out structure.