Incorporation of Thorium in the Zircon Structure Type through the Th 1-x Er x (SiO 4 ) 1-x (PO 4 ) x Thorite-Xenotime Solid Solution.

Pure powdered compounds with a general formula Th1-x Erx (SiO4 )1-x (PO4 )x belonging to the zircon-xenotime family were successfully synthesized under hydrothermal conditions (250 °C, 7 days) as recently reported for the preparation of coffinite. Therefore, a thorough, combined PXRD, EDX, EXAFS, Raman, and FTIR analysis showed the formation of a solid solution in agreement with Vegard's law. Moreover, the examination of the local structure shows that the Th-O distances remain close to those found in ThSiO4 , whereas the Er-O distances show a significant decrease from 2.38(14) to 2.34(7) Å when increasing the erbium content from x = 0.2 to x = 1. The variation of the local structure also affects the PO4 3- groups that are surely distorted in the structure.