Uranyl oxide hydrate phases with heavy lanthanide ions: [Ln(UO2)2O3(OH)]·0.5H2O (Ln = Tb, Dy, Ho and Yb)

Abstract

Four uranyl oxide hydrate phases with heavy lanthanide ions, [Ln(UO₂)₂O₃(OH)]·0.5H₂O [Ln = Tb (1), Dy (2), Ho (3) and Yb (4)], have been synthesized under hydrothermal conditions at 240 °C and characterized. SEM-EDS revealed that these phases have very similar thin plate morphologies with a U to Ln atomic ratio of 2 : 1, which is further confirmed by TEM-EDS. Their high magnification TEM bright field images showed small crystalline domains (∼2–5 nm) with preferred crystal orientations. Both XRD and TEM SAED confirmed that they crystallize in the trigonal crystal system with the Pm1 space group. Raman characterization revealed the typical vibration modes for the uranyl units with the calculated UO bond lengths are comparable to the values reported for other UOH phases with d-transition metal ions as the interlayer species. The possible presence of a pentavalent uranyl unit has been ruled out by UV-vis-NIR spectroscopy. The thermal and optical properties have also been investigated and reported.