XAFS study of six-coordinated silicon in R2O–SiO2–P2O5 (R = Li, Na, K) glasses

The local structures around silicon and phosphorous atoms in R2O–SiO2–P2O5 (R = Li, Na and K) glasses have been investigated using Si and P K-edge XAFS spectroscopy by transmission mode at BL-4 and BL-3 at the synchrotron facility in Ritsumeikan University. As a result of XANES and EXAFS analyzes, six-coordinated silicon atoms were observed in the glasses. The fraction of six-coordinated silicon atom changed with increasing of the concentration of alkali oxide and P2O5. For the change of concentration of alkali oxide, it takes maximum values which are 60% in Li2O, 90% in Na2O and 85% in K2O system at 20 mol% alkali oxide. It gradually increased up for the increase of the concentration of P2O5 to 55% in Li2O, 80% in Na2O and 90% in K2O system. The Si–O inter-atomic distance in the glasses changes from 1.63 to 1.79 Å with increasing the fraction of six-coordinated silicon atom. On the other hand, it was not observed the local structural change around the phosphorous atom.