% IMPORTANT: The following is UTF-8 encoded. This means that in the presence % of non-ASCII characters, it will not work with BibTeX 0.99 or older. % Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or % “biber”. @ARTICLE{Murphy:848119, author = {Murphy, Gabriel L. and Wang, Chun-Hai and Beridze, George and Zhang, Zhaoming and Kimpton, Justin A. and Avdeev, Maxim and Kowalski, Piotr and Kennedy, Brendan J.}, title = {{U}nexpected {C}rystallographic {P}hase {T}ransformation in {N}onstoichiometric {S}r{UO} 4– x : {R}eversible {O}xygen {D}efect {O}rdering and {S}ymmetry {L}owering with {I}ncreasing {T}emperature}, journal = {Inorganic chemistry}, volume = {57}, number = {10}, issn = {1520-510X}, address = {Washington, DC}, publisher = {American Chemical Society}, reportid = {FZJ-2018-03395}, pages = {5948 - 5958}, year = {2018}, abstract = {In situ synchrotron powder X-ray diffraction measurements have demonstrated that SrUO4 undergoes a reversible phase transformation under reducing conditions at high temperatures, associated with the ordering of oxygen defects resulting in a lowering of crystallographic symmetry. When substoichiometric rhombohedral α-SrUO4–x, in space group R3̅m with disordered in-plane oxygen defects, is heated above 200 °C in a hydrogen atmosphere it undergoes a first order phase transformation to a (disordered) triclinic polymorph, δ-SrUO4–x, in space group P1̅. Continued heating to above 450 °C results in the appearance of superlattice reflections, due to oxygen-vacancy ordering forming an ordered structure δ-SrUO4–x. Cooling δ-SrUO4–x toward room temperature results in the reformation of the rhombohedral phase α-SrUO4–x with disordered defects, confirming the reversibility of the transformation. This suggests that the transformation, resulting from oxygen vacancy ordering, is not a consequence of sample reduction or decomposition, but rather represents a change in the energetics of the system. A strong reducing atmosphere is required to generate a critical amount of oxygen defects in α-SrUO4–x to enable the transformation to δ-SrUO4–x but once formed the transformation between these two phases can be induced by thermal cycling. The structure of δ-SrUO4–x at 1000 °C was determined using symmetry representation analysis, with the additional reflections indexed to a commensurate distortion vector k = ⟨1/4 1/4 3/4⟩. The ordered 2D layered triclinic structure of δ-SrUO4–x can be considered a structural distortion of the disordered 2D layered rhombohedral α-SrUO4–x structure through the preferential rearrangement of the in-plane oxygen vacancies. Ab initio calculations using density functional theory with self-consistently derived Hubbard U parameter support the assigned ordered defect superstructure model. Entropy changes associated with the temperature dependent short-range ordering of the reduced U species are believed to be important and these are discussed with respect to the results of the ab initio calculations.}, cin = {IEK-6 / JARA-HPC}, ddc = {540}, cid = {I:(DE-Juel1)IEK-6-20101013 / $I:(DE-82)080012_20140620$}, pnm = {161 - Nuclear Waste Management (POF3-161) / Atomistic modeling of radionuclide-bearing materials for safe management of high level nuclear waste. $(jara0037_20181101)$ / Investigation of the new materials for safe management of high level nuclear waste. $(jara0038_20121101)$}, pid = {G:(DE-HGF)POF3-161 / $G:(DE-Juel1)jara0037_20181101$ / $G:(DE-Juel1)jara0038_20121101$}, typ = {PUB:(DE-HGF)16}, pubmed = {pmid:29714481}, UT = {WOS:000433013600026}, doi = {10.1021/acs.inorgchem.8b00463}, url = {https://juser.fz-juelich.de/record/848119}, }