| Abstract
| - Microcrystals of the first ammonium-thorium phosphates, (NH4)2Th(PO4)2·H2O (tetragonal, I41/amd, a = 7.0192(4) Å, c = 17.9403(8) Å) and NH4Th2(PO4)3 (monoclinic, C2/c, a = 17.880(6) Å, b = 6.906(1) Å, c = 8.152(2) Å, β = 104.39(2)°) were hydrothermally obtained from a Th(NO3)4-CO(NH2)2-H3PO3-H2O system (T = 180 °C). In both cases, the structure consists of a three-dimensional framework with PO4 tetrahedra coordinated to Th atoms (ThOn polyhedra, where n = 8 or 9, for the tetragonal or monoclinic phase, respectively). The ammonium ions (and water molecules) are located in the tunnels.
- In the field of the specific immobilization of radionuclides such as actinides coming from the reprocessing of spent nuclear fuel, several phosphate matrixes have been extensively studied. However, in spite of numerous efforts, the family of structurally characterized thorium phosphates is still small. In this study, microcrystals of both (NH4)2Th(PO4)2·H2O and NH4Th2(PO4)3 were hydrothermally obtained from a Th(NO3)4-CO(NH2)2-H3PO3-H2O system. The structure of these three-dimensional compounds, the first reported ammonium-thorium phosphates, were solved by X-ray powder diffraction data.
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