Charge Transfer Between Ce and Fe During Cooling of an Aluminosilicate Melt: An <i>In Situ</i> XANES Investigation

Multivalent elements are often incorporated into silicate glasses to enhance specific properties of the final product. However, for some of them, these properties strongly depend on the redox state of the multivalent elements. While the redox behavior of glasses containing a single multivalent element is well studied, research on the <i>in situ</i> interaction between multiple multivalent elements is scarce. In this study, <i>in situ</i> XANES spectroscopy was used to investigate the high-temperature redox state of both Ce and Fe in an aluminosilicate melt. The results were compared to room temperature measurements. Our findings demonstrate that, at high-temperature equilibrium, Ce and Fe act independently. However, upon cooling below 900 °C, a charge transfer process occurs between the two elements as described by the reaction Ce⁴⁺ + Fe²⁺ → Ce³⁺ + Fe³⁺. The existence of such a charge transfer, observed even in melts doped with very low Ce and Fe amounts, could suggest that both elements are not randomly distributed in the melt. The intensity of the charge transfer process depends on the CeO₂/FeO ratio, with the element present in excess showing minimal change in redox state upon cooling. This explains the difference in room temperature redox state between samples.