The fluorite related modulated structures of the Gd2(Zr2−xCex)O7 solid solution: An analogue for Pu disposition

We present an overview of the Gd2(Zr2−xCex)O7 phase diagram, of interest as a model system for ceramic disposition of Pu (with Ce as a Pu surrogate). The fluorite related structures of this solid solution were determined using a modulated structure approach, to identify the underlying cation and vacancy ordering mechanisms from analysis of key satellite reflections in selected zone axis electron diffraction patterns. This revealed the formation of four structure types: pyrochlore for x<0.25, defect fluorite for 0.51.50. X-ray absorption (XAS) and electron energy loss (EELS) spectra confirmed the presence of Ce4+ as the dominant species in compositions across this system, remaining analogous to Pu4+. - Graphical abstract: Electron diffraction reveals the cation vacancy ordering mechanisms leading to fluorite related superstructures in the Gd2(Zr2−xCex)O7 solid solution. Highlights: ► The fluorite related solid solution Gd2(Zr1−xCex)O7 was prepared by solid state synthesis. ► Ce L3 edge XAS and Ce M4,5 EELS measurements show Ce substitutes as Ce4+. ► Cation and oxygen vacancy ordering results in four fluorite related structures.