The structure of BaSr4U3O14 and a structural and thermodynamic characterization of Sr5U3O14

The structures of Sr5U3O14 and BaSr4U3O14 have been studied by X-ray powder diffraction and neutron powder diffraction. Both compounds could be indexed on a pseudo-tetragonal, chiolite-type structure. Sr5U3O14 was shown to be orthorhombic and to have space group Pbca with a = 11.2416(7) Angstrom, b = 11.2572(7) Angstrom, c = 11.0791(4) Angstrom, and Z = 4. BaSr4U3O14 was shown to be orthorhombic and to have space group Cmca with a = 11.3647(7) Angstrom, b = 11.3770(7) Angstrom, c = 11.0203(5) Angstrom, and Z = 4. The thermodynamic properties of Sr5U3O14 at 298.15 K have been determined, and its thermal stability with respect to the neighboring strontium uranate phases are discussed. (C) 1999 Academic Press.