Incorporation of Thorium in the Zircon Structure Type through the Th1–xErx(SiO4)1–x(PO4)xThorite–Xenotime Solid Solution

Pure powdered compounds with a general formula Th1–xErx(SiO4)1–x(PO4)xbelonging 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 PO43–groups that are surely distorted in the structure.