Quantitative determination of cerium oxidation states in alkali-aluminosilicate glasses using M4,5-edge XANES

Abstract

A calibration method for quantitative determination of Ce4+/Ce3+ in alkali-aluminosilicate glasses using Ce M4,5-edge X-ray absorption near edge structure (XANES) spectroscopy is presented. Samples of varying alkali oxide content synthesized over a range of temperatures and oxygen fugacities (fO2) were analyzed using both synchrotron-based XANES and traditional wet chemical techniques. Based on comparison to potentiometric determinations of Ce4+/Ce3+ in digested portions of our samples, Ce4+ was found to have a greater fluorescence yield (FLY) response to the incident radiation in the M4,5-edge XANES region than Ce3+. This results in an overestimation of the Ce4+/Ce3+ ratio when directly comparing the contributions of the two oxidation states to the total M-edge area, as has been used for crystalline materials. We offer a correction to M-edge determined Ce4+/Ce3+ ratios as follows:Ce4+/ΣCe=578.7Ce4+/ΣCe±5%XANESA±0.0040<Ce4+/ΣCe<0.4where the exponent A is a function of the number of non-bridging oxygens per tetrahedrally-coordinated cation (NBO/T) for a given glass composition, [Ce4+/ΣCe]XANES is the contribution from Ce4+ to the M4,5-edge area over the total area of the M4,5-edge, and Ce4+/ΣCe is the actual fraction of Ce4+ in the sample. The FLY response of Ce4+ was found to systematically increase with the degree of polymerization of the glass, suggesting that in addition to the local electronic environment, the FLY response of Ce is also dependent on longer range interactions.