Structural and thermal studies of SrU(PO4)2 and BaU(PO4)2

Compounds SrU(PO4)(2) (SUP) and BaU(PO4)(2) (BUP) were synthesized by solid state method in high purity argon atmosphere at 1473 K. Structures of both the compounds were derived using Rietveld method from powder X-ray diffraction (XRD) data. Compound SUP is orthorhombic and has ordered cheralite type structure with alternate layers of SrO10 and UO8 polyhedra. Compound BUP is monoclinic and has a non cheralite structure with Ba and U in 14 and 8 coordinations, respectively. Thermogravimetric (TG) curves obtained by heating both the compounds in air confirm the oxidation of U(IV) to U(VI) between 600 and 1573 K. High temperature XRD data collected in vacuum up to 1473 K indicated positive thermal expansion for both the compounds. Heat capacity (C-p) measurements were also carried out for both the compounds by heat flow Differential Scanning Calorimeter (DSC) in argon atmosphere from 300 to 873 K. (C) 2017 Elsevier B.V. All rights reserved.