Abstract
Sodium borosilicate glasses (Na2O-B2O3-SiO2) undergone several heat treatment were examined by mean of XANES spectroscopy (B-K edge) using synchrotron ultra-soft X-ray. The p* peak located at ~194 eV, which reflects tetraborate unit shifted discontinuously to higher energy side at around 500°C, suggesting that the proportion of the tetraborate unit increases above the temperature.