Structural and thermal studies on Na2U(MoO4)3 and Na4U(MoO4)4

In Na-U(IV)-Mo-O system, two quaternary compounds Na2U(MoO4)3 and Na4U(MoO4)4 were prepared by solid state reactions of Na2MoO4, UMoO5 and MoO3 in the required stoichiometric ratio at 500 deg C in evacuated sealed quartz ampoules. The crystal structure of both the compounds were derived from X-ray powder diffraction data in the tetragonal system by Rietveld profile method. Na2U(MoO4)3 has scheelite structure, whereas Na4U(MoO4)4 has scheelite superlattice structure. TG curves of Na2U(MoO4)3 and Na4U(MoO4)4 did not show any significant weight change up to 750 deg C in an inert atmosphere. During the heating cycle in an inert atmosphere, DTA curves of Na2U(MoO4)3 and Na4U(MoO4)4 showed endothermic peaks due to the melting of the compounds at 740 deg C and 730 deg C, respectively. Na2U(MoO4)3 and Na4U(MoO4)4, when heated in air atmosphere at 1200 deg C, decomposed to form Na2U2O7 which was confirmed by weight loss calculation and XRD.