Detailed X-ray diffraction analysis of Ce_1-xNd_xO_2-(x/2) as a surrogate for substoichiometric americium oxide

European Space Agency (ESA) radioisotope power systems will use ²⁴¹Am as their heat source. The chemical form of the americium oxide has yet to be decided but an option that may be investigated in future research are certain Ia-3 AmO_2-(x/2) phases. In a previous investigation, Ia-3 (C-type) Ce_1-xNd_xO_2-(x/2) with x values between 0.5 and 0.7 were proposed as candidate surrogates (Watkinson et al., 2017). A continuous oxalate precipitation and calcination route for fabricating such oxides was presented and the means to target an x value was described (Watkinson et al., 2017). An initial estimate of the lattice parameter was provided in the previous study by fitting Gaussians to X-ray diffraction data peaks. Previous quantitative X-ray fluorescence analysis suggested an x-value of 0.61 had been achieved. Characterising the crystal structure and the oxygen-to-metal ratio, which corresponds to x, of an oxide powder will be essential data for future sintering studies where changes in these parameters will be investigated. In this study, a Rietveld refinement investigation is presented, which has enabled the lattice parameter of the material to be better constrained and estimated more precisely. The result is consistent with the literature; a lattice parameter-x value relationship in the literature was used to estimate the x value using this improved estimate and it confirmed an x value of 0.6 has been made. This investigation has thus further validated the previously presented synthesis method and characterised the crystal structure of the material more precisely in preparation for future sintering trials.