Hydrogen Impurity Effects. A5Tt3 Intermetallic Compounds between A=Ca, Sr, Ba, Eu and Tt=Si, Ge, Sn with Cr5B3-like Structures that are Stable Both as Binary and as Ternary Hydride and Fluoride Phases

Because of its low solubility in water and high thermal stability, thorium phosphate diphosphate (TPD), Th4(PO4)4P2O7, seems to be a very good matrix for radionuclide immobilization. During the leaching studies of this compound the formation of a new phase, different from the TPD was observed. In order to identify this phase, two other thorium phosphates: thorium phosphate–hydrogenphosphate (TPHP), Th2(PO4)2HPO4·H2O, and thorium hydroxide phosphate (THOP), Th(OH)PO4, were synthesized in hydrothermal conditions then characterized. It appeared that the neoformed phase was identical to the TPHP.