In situ diffraction from levitated solids under extreme conditions-structure and thermal expansion in the Eu₂O₃-ZrO₂ system

The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500°C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200°C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu₂O₃-ZrO₂ binary system were investigated, including the high-temperature order-disorder transformation in Eu₂Zr₂O₇. The disordered fluorite phase is found to be stable above 1900°C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu₂Zr₂O₇ show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6-12.0 × 10^-6C^-1. These studies open new vistas for in situ exploration of complex structural changes in high-temperature materials.