Local Ordering Around Tetrahedral Co ²⁺ in Silicate Glasses

Alkali lime silicate glasses containing 5 wt% of CoO were investigated by Co K‐edge XANES and EXAFS and optical absorption spectroscopy. Our results reveal the presence of tetrahedral Co 2+ connected with the glass network, with a IV Co–O–Si angle of 134°. Changing the alkali from K + to Na + induces an increase of the local disorder around Co 2+ , as shown by a decrease of the contribution from the second neighbors in the EXAFS signal. We propose two models for interpreting the structure of the second shell of neighbors. Our results provide a structural basis for rationalizing the optical properties of Co 2+ species in glasses.