Structure of alkali germanate glasses studied by spectroscopic techniques

EXAFS spectra and X-ray radial distribution curves were determined for Li2OGeO2, Na2OGeO2 and K2OGeO2 glasses to elucidate the glass structure. The formation of 6-coordinated Ge atoms on the addition of an alkali oxide R2O to GeO2 glass was confirmed. The concentration of 6-coordinated Ge atoms N6 increased with an increase of the R2O content, exhibited a maximum around 20 mol% R2O and decreased again with a further increase of the R2O content. No essential dicrepancies between the techniques employed and between the glass systems investigated were found in the N6 value and the R2O content of glass at the maximum. The small discrepancies were attributed to the different assumptions made for the calculations. It was concluded that the concentration of 6-coordinated Ge atoms N6 follows the formula N6=x/(100-x), where x is mol% R2O. The maximum value of N6 was about 25% for the composition of about 20 mol% R2O.