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+.