Thermal expansion studies on UMoO5, UMoO6, Na2U(MoO4)3 and Na4U(MoO4)4

In the present work, thermal expansion behavior of lower valent sodium uranium molybdates, i.e., Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were studied under vacuum in the temperature range of 298-873 K using high temperature X-ray diffractometry (HTXRD). Expansion behaviors of UMoO₅ and UMoO₆ were also studied in vacuum from 298 to 873 K and 773 K, respectively. UMoO₅ was synthesized by reacting UO₂ with MoO₃ in equi-molar proportion in evacuated sealed quartz ampoule at 1173 K for 14 h. Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were prepared by reacting UMoO₅ and MoO₃ with 1 and 2 moles of Na₂MoO₄, respectively, at 873 K in evacuated sealed quartz ampoule. XRD data of UMoO₅ and UMoO₆ were indexed on orthorhombic and monoclinic systems, respectively, whereas, the data of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the four compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 873 K.