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.