Crystal Structure and Phase Transitions of Gd(CO 3 )OH Studied by Synchrotron Powder Diffraction

The crystal structure of Gd(CO 3 )OH was solved using synchrotron powder X‐ray diffraction. Gd(CO 3 )OH was known to exist in a form Gd 2 O(CO 3 ) 2 ·H 2 O and its powder pattern has been listed in JCPDF (#430604) for decades, but the crystal structure has not yet been elucidated. The crystal structure is solved with simulated annealing and the DASH program. The final Rietveld refinement converged to R wp =6.28%, R p = 4.47%and χ 2 = 1.348, using the GSAS program. Gd(CO 3 )OH crystallizes in orthorhombic system with lattice parameters a = 7.08109(9), b = 4.88436(7), c = 8.45010(13)Å and space group P nma . Gd(CO 3 )OH forms a three‐dimensional framework with an eight‐membered ring, a one‐dimensional channel and OH − in the cavity. XANES of Gd L III ‐edge indicates that the oxidation state of Gd is 3+. Two phase transitions of Gd(CO 3 )OH were found at 500 and 650 °C to yield Gd 2 O 2 CO 3 and Gd 2 O 3 respectively.