Targeting complex plutonium oxides by combining crystal chemical reasoning with density-functional theory calculations: the quaternary plutonium oxide Cs₂PuSi₆O₁₅

Abstract

The stability of the novel Pu(IV) silicate, Cs2PuSi6O15, was predicted from a combination of crystal chemical reasoning and DFT calculations and confirmed by its synthesis via flux crystal growth. Formation...

Chloride Reduction of Mn3+ in Mild Hydrothermal Synthesis of a Charge Ordered Defect Pyrochlore, CsMn2+Mn3+F6, a Canted Antiferromagnet with a Hard Ferromagnetic Component

“…The measured magnetic moment per formula unit of 8.01 μ B is above the theoretical value of 7.68 μ B that was calculated using the spin-only magnetic moments for Mn 2+ and Mn 3+ cations, 5.92 and 4.90 μ B , respectively. Although higher experimental magnetic moments for Mn 3+ have been previously reported and can be one possible explanation of higher than expected paramagnetic moment of CsMn 2 F 6 , , the moment can also be adjusted to lower values by including a small temperature independent paramagnetic (TIP) component. While fitting the data to a modified Curie–Weiss law results in a negligibly small negative χ 0 (χ 0 ∼ −0.00009 emu/mol), using a small positive χ 0 of 0.0011 emu/mol results in a magnetic moment of 7.66 μ B (Figure S5), which is in good agreement with the expected theoretical value of 7.68 μ B , and insignificantly decreases the quality of the data fit, see Figure S5.…”

A Density-Functional Theory Structural Database for Discovery of Novel Actinide Waste Forms

“…Even though the database contains many examples of actinide materials, we limited our scope to oxide-framework crystal structures that contained both an actinide/lanthanide element and an alkali cation, with the exception of Li, as it is much more covalent than the other alkali metals and hence not as representative. Silicates are known to form stable salt inclusion materials (SIMs); ,,,− however, our aim was to go beyond these more established framework materials and instead search for As, Mo, P, and V oxides containing Ce, Th, or U. In order to simplify our computational efforts, we excluded crystal structures with partial lattice site occupancies.…”

“…One can use crystal chemical understanding, such as oxidation-state-specific preferred coordination environments and ionic radii, to hypothesize new waste form compositions. For instance, cerium complexes, by virtue of their size and coordination environments, are likely to accommodate plutonium as well and thus can be used to propose and synthesize plutonium analogues . However, the synthesis of one TRU-containing waste form does not guarantee the successful synthesis of another and the complexity of carrying out exploratory chemistry with TRU elements suggests that other approaches need to be explored.…”

“…However, the synthesis of one TRU-containing waste form does not guarantee the successful synthesis of another and the complexity of carrying out exploratory chemistry with TRU elements suggests that other approaches need to be explored. Coupling the knowledge of inorganic crystal structures with computational approaches, such as that used for generating computational databases, can efficiently screen thousands of compounds to find new target compositions for TRU phases, allowing efficient experimental investigations. − …”

Rb2Ln[Si2O6]F (Ln = Y, Eu–Lu): Flux Synthesis, Structure Determination, and DFT-Calculated Formation Enthalpies of a Series of Mixed-Anion Rare Earth Cyclosilicates

“…We are applying this methodology as an early screening tool to build on our previous work that demonstrated the utility of DFT-computed formation enthalpies for yielding dependable estimations of the relative stability of TRU containing silicates in order to follow up, when warranted, with attempts at synthesizing the TRU containing compositions. 24,25 Here we report on a new series of mixed-anion alkali rare earth silicate fluorides with the composition Rb 2 Ln[Si 2 O 6 ]F °C at 6 °C/h. The mixtures were then cooled to room temperature by turning off the furnace.…”