Isostructural crystal hydrates of rare-earth metal oxalates at high pressure: from strain anisotropy to dehydration

Abstract

Abstract The crystal structures of a series of isostructural rare-earth metal oxalates, (REE)2(C2O4)3·10H2O (REE=Sm, Y) and a 1:1 YSm(C2O4)3·10H2O solid solution, have been studied in situ by single-crystal X-ray diffraction and optical microscopy. The structures were followed from ambient pressure to 6 GPa in a DAC with paraffin as the hydrostatic fluid. Bulk compressibilities, anisotropic lattice strain on hydrostatic compression and the corresponding changes in the atomic coordinates were followed. Discontinuities/sharp changes in the slopes of the pressure dependences of volume and selected cell parameters have been observed for yttrium-containing salts at ~3.5 GPa. This may be related to the re-distribution of water molecules within the crystal structure. Y2(C2O4)3·10H2O undergoes a partial dehydration at 1 GPa, forming monoclinic Y2(C2O4)3·6H2O as single-crystalline inclusions in the original phase.