Lanthanides in silicate glasses: A vibrational spectroscopic study

Abstract

Parallel‐ and perpendicular‐polarized Raman and KBr pellet transmission IR spectra of quenched 10K2O‐50SiO2‐nR2O3 (R = La, Gd, Yb; n = 0, 1, 5, 10 mol) glasses are presented. Increasing lanthanide oxide concentration produces partially‐polarized high‐frequency bands at 1030, 940, and 860 cm−1, assigned to the symmetric stretching modes of SiO4 tetrahedra containing 1, 2, and 4 nonbridging oxygen, respectively, in which the nonbridging oxygen coordinate primarily with lanthanides. Lanthanides therefore form silicate anions that are depolymerized relative to the bulk liquid and which have no counterparts in R2O3‐SiO2 binary systems. The spectra indicate that there is little sharing of nonbridging oxygen by K and lanthanides. The spectra of glasses containing different lanthanides at the same concentration are qualitatively and quantitatively very similar. Lanthanides have energetically unfavorable interactions with the network structure of polymerized liquids compared to cations of lower valence. If lanthanides coordinate nonbridging oxygen without the aid of K, then lanthanide saturation concentrations will show modest increases with increasing (Na,K)/Al in peralkaline liquids, except in liquids in which P2O5 concentration is comparable to the total lanthanide concentration. Since differences in lanthanide ionic radii have small effects upon the spectra, lanthanide solution mechanisms in silicate glasses (and by inference silicate liquids) are probably very similar.