Evolution of the local environment of lanthanum during simplified SON68 glass leaching

The evolution of the short- and medium-range local environment of lanthanum was determined by L_III-edge X-ray absorption spectroscopy (XAS) during leaching of simplified SON68-type glasses. In glass without phosphorus, lanthanum is found in a silicate environment, and its first coordination sphere comprises eight oxygen atoms at a mean distance of 2.51 Å. When this glass was leached at a high renewal rate, the lanthanum local environment was significantly modified: it was present at hydroxycarbonate and silicate sites with a mean La-O distance of 2.56 Å, and the second neighbors consisted of La atoms instead of Si for the glass. Conversely, in the gel formed at low renewal rates, lanthanum was found in a silicate environment similar to that of the glass. In phosphorus-doped glass, lanthanum is found in a phosphate environment, although the Si/P atomic ratio is 20:1. Lanthanum is surrounded by seven oxygen atoms at a mean distance of 2.37 Å. When phosphorus-doped glass is leached, regardless of the leaching solution flow rate, the short- and medium-range lanthanum local environment remains almost constant; the most significant change is a 0.05 Å increase in the La-O distance.