Phase study in the Na-Sr-U-O system: Characterization of new phase

In continuation with the earlier work for phase studies of Rb-Sr-U-O and Cs-Sr-U-O systems, the subsolidus phase relations in Na-Sr-U-O quaternary system were determined at 850 °C in air atmosphere. A novel quaternary phase Na₈Sr₂U₆O₂₄ in the Na-Sr-U-O system was synthesized by heating the respective oxides at 850 °C in air. XRD data of Na₈Sr₂U₆O₂₄ was indexed on a cubic system with lattice parameter a = 0.8326 nm and was found isostructural with K₈Sr₂U₆O₂₄ and Rb₈Sr₂U₆O₂₄. A pseudo-ternary phase diagram of Na₂O-SrO-UO₃ was drawn using the new quaternary compound and various phase fields were established by X-ray powder diffraction analysis. The structure of Na₈Sr₂U₆O₂₄ was derived from the powder data and structural parameters were refined by the Rietveld profile method.