XAS investigation of rare earth elements in sodium disilicate glasses

The structural environment of rare earth elements (REE) in synthetic silicate glasses of Na2Si2O5 composition has been characterized through extended X-ray absorption fine structure spectroscopy (EXAFS) at the respective rare-earth LIII-edges, in order to obtain oxidation state, coordination number and <REE–O> bond distances. In these glasses, synthesised in air and at room pressure, the studied lanthanide ions are in the trivalent state. The EXAFS-determined <REE–O> distances decrease with an increase in atomic number of the rare-earth ions. The lanthanides are all octahedrally coordinated, with a well-defined first coordination sphere around rare-earth ions, and with no indication of a longer-range order. To ascertain the possible presence of REE–REE clustering, several EXAFS fits have also been performed starting from different model structures including REE also in the second coordination shell. No evidence has been found in these glasses of REE–O–REE bridges.