Synthesis and crystal structure investigations of ternary oxides in the Na–Pu–O system

Highlights: • Crystalline phases in the Na–Pu–O system were obtained by solid state synthesis. • Structures of these phases were studied by the powder X-ray diffraction. • New crystalline forms of Na₅PuO₅ and Na₃PuO₄ were observed for the first time. • High-temperature X-ray diffraction studies were performed for Na₄PuO₅ and Na₅PuO₆. • Phase diagram for the ternary Na–Pu–O system was reassessed. - Abstract: Ternary oxides of sodium and plutonium in oxidation states from +4 to +7 have been synthesized by solid state reactions at elevated temperatures in pure argon or oxygen atmospheres. Crystal structures of the obtained phases have been investigated by the Rietveld method using conventional X-ray powder diffraction technique. The structural analogs were found among the families of complex oxides of alkali elements and cerium, ruthenium, antimony, uranium/neptunium and osmium. The new results were compared to earlier literature data for the Na–Pu–O system