Structural studies of potassium silicate glasses with fixed iron content and their relation to similar alkali silicates

Abstract

Silicate glasses containing potassium oxide of molar percentages 12 percent, 16 percent and 20 percent each with 8 percent iron oxide have been prepared and examined by Raman, Extended X-ray absorption fine structure (EXAFS) and Mossbauer spectroscopy. For the 12 percent and 16 percent of iron potassium silicate glasses, analysis of the Raman data indicated a maximum of Q sup(2) linkages of the silica tetrahedra while for the 20 percent iron potassium silicate sample, the Q sup(3) and Q sup(4) linkages were dominant. EXAFS data found the Fe ion to be in tetrahedral coordination with oxygen and a Fe-O distance of approx. 1.85 Angstrom. The isomeric shifts in the Mossbauer spectra found the Fe sup(3+) to Fe sup(2+) ratios to vary with potassium content from 2:1 for the 12 percent to 8:1 for the 20 percent potassium glass. Spectral areas showed iron ions to be tetrahedrally coordinated to oxygen with quadrupole splitting showing distortion of these units. From the distribution of Q sup(n) linkages it is found that at 16 mol percent of the alkali, the lithium iron silicates have more open structures than the sodium and potassium iron silicate glasses. The more open structure of sodium silicate glass when iron is added could have important implications for its use as an electrolytic material.