Abstract
Phase formation in the mixed sulfate-selenate Np(VI)-bearing aqueous system has been investigated. The obtained crystalline compounds, Cs2[(NpO2)2(TO4)3] (T = S, Se), crystallize in the tetragonal system, space group P4 21m, with a = 9.5737(3)-9.817(3) Å, c = 8.0824(4)-8.111(3) Å, and V = 740.79(6)-781.8(6) Å3, and have been chemically characterized. Single-crystal X-ray diffraction experiments at various temperatures were used to define the thermal behavior of the crystal structures relative to the S/Se ratio. The thermal behavior of mixed sulfate-selenate and pure selenate compounds is anisotropic, with the highest thermal expansion in the direction perpendicular to the sheets of Np-bearing polyhedra, while the structure of the pure sulfate compound experiences almost isotropic thermal expansion with slightly higher expansion within the layer, which is explained by the influence of stronger Cs-O bonding. High-temperature drop solution calorimetry was used to derive the enthalpies of formation of the Cs+-bearing neptunyl oxysalts. Within this family of isotypic structures, cesium neptunyl sulfate has a more negative enthalpy of formation in comparison to the selenate compound.
| Original language | English |
|---|---|
| Pages (from-to) | 2811-2819 |
| Number of pages | 9 |
| Journal | Crystal Growth and Design |
| Volume | 19 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 1 2019 |
| Externally published | Yes |
Funding
This work was supported by the Office of Basic Energy Sciences of the U.S. Department of Energy as part of the Materials Science of Actinides Energy Frontier Research Center (DESC0001089), St. Petersburg State University (to V.V.G., 3.42.729.2017) and by the President of Russian Federation grants for young scientists (to V.V.G. and I.V.K., no. MK-4810.2018.5). The ICP-OES analyses were conducted at the Center for Environmental Science and Technology (CEST), at the University of Notre Dame. PXRD, TGA, and high-temperature calorimetry data were collected at the Materials Characterization Facility supported by the Center for Sustainable Energy at the University of Notre Dame (ND Energy). ICP-MS analyses were done at the Midwest Isotopic and Trace Element Research Analytical Center (MITERAC) facility at the University of Notre Dame.