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%, 16% and 20% each with 8% iron oxide have been prepared and examined by Raman, Extended X-ray absorption fine structure (EXAFS) and Mossbauer spectroscopy. For the 12% and 16% of iron potassium silicate glasses, analysis of the Raman data indicated a maximum of Q2 linkages of the silica tetrahedra while for the 20% iron potassium silicate sample, the Q3 and Q4 linkages were dominant. EXAFS data found the Fe ion to be in tetrahedral coordination with oxygen and a Fe O distance of ~1.85 A. The isomeric shifts in the Mossbauer spectra found the Fe3+ to Fe2+ ratios to vary with potassium content from 2:1 for the 12% to 8:1 for the 20% 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 Qn linkages it is found that at 16 mol% 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.