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.