Local surrounding of cobalt atoms in borosilicate glasses

The state and distribution of cobalt atoms in sodium-borosilicate (1) and multicomponent borosilicate (2) glasses of complex composition were studied by the method of EXAFS (extended X-ray absorption fine structure) spectroscopy. In glasses 1, in which boron parts in three- and four-coordinated states are approximately equal, ions of two-charge cobalt are in tetragonal oxygen surrounding and they are homogeneously distributed in the glass matrix. In glasses 2, containing alkali and alkaline earth modifiers, cobalt is both in tetrahedral, and octahedral surrounding. With increase in CoO concentration in the glasses the number of cobalt-oxygen polyhedrons bond with each other by vertices and ribs, increases. Increase in the content of Na₂O or Na₂O-base radioactive waste oxides results in a more regular distribution of cobalt. Dependence of cobalt leaching out rate of the glasses on their composition passes through an extreme point, which is related to structural reconstructions in the glasses.