Uranyl peroxide nanoclusters at high-pressure
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Jennifer E.S. Szymanowski Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA
Fuxiang Zhang Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
Yu Lin Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
Brendan T. McGrail Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA
Wendy L. Mao Department of Geological Sciences, Stanford University, Stanford, California 94305, USA; and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
Peter C. Burns Department of Civil & Environmental Engineering & Earth Sciences and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
Rodney C. Ewing Department of Geological Sciences, Stanford University, Stanford, California 94305, USA (Received 11 May 2017; accepted 30 June 2017)
U60 ([UO2(O2)(OH)]6060 in water) is a uranyl peroxide nanocluster with a fullerene topology and Oh symmetry. U60 clusters can exist in crystalline solids or in liquids; however, little is known of their behavior at high pressures. We compressed the U60-bearing material: Li68K12(OH)20[UO2 (O2)(OH)]60(H2O)310 (Fm3; a 5 37.884 Å) in a diamond anvil cell to determine its response to increasing pressure. Three length scales and corresponding structural features contribute to the compression response: uranyl peroxide bonds (,0.5 nm), isolated single nanoclusters (2.5 nm), and the long-range periodicity of nanoclusters within the solid (.3.7 nm). Li68K12(OH)20[UO2 (O2)(OH)]60(H2O)310 transformed to a tetragonal structure below 2 GPa and irreversibly amorphized between 9.6 and 13 GPa. The bulk modulus of the tetragonal U60-bearing material was 25 6 2 GPa. The pressure-induced amorphous phase contained intact U60 clusters, which were preserved beyond the loss of long-range periodicity. The persistence of U60 clusters at high pressure may have been enhanced by the interaction between U60 nanoclusters and the alcohol pressure medium. Once formed, U60 nanoclusters persist regardless of their associated long-range ordering—in crystals, amorphous solids, or solutions.
I. INTRODUCTION
Uranyl peroxide nanoclusters are the only sizable group of actinide-based polyoxometallates (POMs). They are nano-sized cage-clusters with uranyl ions, UO221, bridged through bidentate peroxide. The dihedral uranyl peroxide angle varies between 135 and 165°, and this curvature induces the formation of the cluster.1–4 Dozens
Contributing Editor: William J. Weber a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.301
of nanocluster topologies exist containing from 20 to 124 uranyl metal centers in the cluster cage.1,5–19 Uranyl peroxide nanoclusters are designated by the number of uranyl metal centers in
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