Flux Synthesis of Alkaline-Earth Lanthanide Borates as Potential Nuclear Waste Forms.

Neodymium is typically considered the best surrogate for trivalent americium and can be used to identify Am containing materials that are likely to form. We have explored the alkaline-earth lanthanide borate phase space using alkaline-earth halide/carbonate fluxes. This resulted in the synthesis of new compounds AELn(BO)X (AE = Ca, Sr; Ln = Pr, Nd, Eu, Tb; X = Cl, Br) and AELn(BO) (AE = Sr, Ba; Ln = Pr, Nd) as well as the synthesis of two compounds of BaLn(BO)(BO) (Ln = Eu, Tb) crystallizing in a new structure type.

Incorporating solvent effects in DFT: insights from cation exchange in faujasites.

Zeolites are versatile materials renowned for their extra-framework cation exchange capabilities, with applications spanning diverse fields, including nuclear waste treatment. While detailed experimental characterization offers valuable insight, density functional theory (DFT) proves particularly adept at investigating ion exchange in zeolites, owing to its atomic and electronic resolution. However, the prevalent occurrence of zeolitic ion exchange in aqueous environments poses a challenge to conventional DFT modeling, traditionally conducted in a vacuum.

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

A new series of mixed-anion alkali rare earth silicate fluorides with composition RbLn[SiO]F (Ln = Y, Eu-Lu) has been synthesized via an alkali chloride/fluoride eutectic flux synthetic route. All synthesized compositions crystallize in the tetragonal space group 4/ with a 3D framework consisting of LnOF octahedra, tetrasilicate rings, and 1D channels containing alkali metals. A combination of powder X-ray diffraction, single-crystal X-ray diffraction, and luminescence emission spectroscopy was performed to characterize the reaction products.

Flux Synthesis, UV-vis Absorbance, and Magnetism of Cesium Copper Silicates with an Isolated Super-Super Exchange Spin Dimer in CsCuSiO.

Single crystals of four new cesium copper silicates were grown from CsCl/CsF flux. [CsCsCl][CuSiO] is a salt-inclusion compound that crystallizes in space group 4/ with lattice parameters = 12.2768(3) Å and = 8.

Flux Crystal Growth of the Extended Structure Pu(V) Borate Na(PuO)(BO).

As part of our exploration of plutonium-containing materials as potential nuclear waste forms, we report the first extended structure Pu(V) material and the first Pu(V) borate. Crystals of Na(PuO)(BO) were grown out of mixed hydroxide/boric acid flux and found to crystallize in the orthorhombic space group with lattice parameters of = 9.9067(4) Å, = 6.

Developing Waste Forms for Transuranic Elements: Quaternary Neptunium Fluorides of the Type NaMNpF (M = Ti, V, Cr, Mn, Fe, Co, Ni, Al, Ga).

A series of quaternary Np(IV) fluorides was synthesized using a mild hydrothermal synthesis approach. The compositions are all of the type NaMNpF, where M = Ti(III), V(III), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Al(III), and Ga(III) and = 4 for divalent metals, = 3 for trivalent metals. The compounds all crystallize in the -31 space group and are isotypic with actinide analogues NaMAnF (An = Ce, U, Th, Pu).

Crystallization of ALn(BO) (A = Na, K; Ln = Lanthanide) from a Boric Acid Containing Hydroxide Melt: Synthesis and Investigation of Lanthanide Borates as Potential Nuclear Waste Forms.

A series of alkali metal rare-earth borates were prepared via high-temperature flux crystal growth, and their structures were characterized by single crystal X-ray diffraction (SXRD). NaLn(BO) (Ln = La-Lu) crystallize in the monoclinic space group 2/, the potassium series KLn(BO) (Ln = La-Tb) crystallize in the orthorhombic space group while the Ln = Dy, Ho, Tm, Yb analogues crystallize in the orthorhombic space group . To demonstrate the generality of this synthetic technique, high-entropy oxide (HEO) compositions KNdEuGdDyHo(BO) and KNdEuHoTmYb(BO) were obtained in single crystal form.

Interplay between London Dispersion, Hubbard , and Metastable States for Uranium Compounds.

High-throughput computational studies of lanthanide and actinide chemistry with density-functional theory are complicated by the need for Hubbard corrections, which ensure localization of the f-electrons, but can lead to metastable states. This work presents a systematic investigation of the effects of both Hubbard value and metastable states on the predicted structural and thermodynamic properties of four uranium compounds central to the field of nuclear fuels: UC, UN, UO, and UCl. We also assess the impact of the exchange-hole dipole moment (XDM) dispersion correction on the computed properties.

Flux Growth of Uranyl Titanates: Rare Examples of TiO Tetrahedra and TiO Square Bipyramids.

Single crystals of four new uranyl titanates have been grown via the flux growth method using mixed alkali halide fluxes. Na(UO)(TiO)O and KNa(UO)(TiO)O have analogous layered structures containing titanyl (TiO) units coordinated into TiO square pyramids. Cs(UO)TiO crystallizes in the CsUSiO structure type and is a rare example of a structure containing TiO tetrahedra.

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

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 enthalpies of the A2MSi6O15 (A = Na-Cs; M = Ce, Th, U-Pu) compositional family were calculated and indicated the Cs-containing phases should preferentially form in the Cmc21 structure type, consistent with previous experimental findings and the novel phases produced in this work, Cs2PuSi6O15 and Cs2CeSi6O15. The formation enthalpies of a second set of compositions, A2MSi3O9, were also calculated and a comparison between the two compositional families correctly predicted A2MSi6O15 to be on average more stable than A2MSi3O9.

Expansion of the Na M (Ln/An) F Series: Incorporation of Plutonium into a Highly Robust and Stable Framework.

Na MAn F is an extremely versatile framework structure for incorporating tetravalent actinides (An) and cerium along with divalent or trivalent d-metals (M); moreover, the structure exhibits a high resistance to harsh chemical conditions. This extreme robustness can potentially be exploited for the sequestration of plutonium in a stable matrix; however, no Na MPu F compounds have been reported so far. Herein, we present four new plutonium fluorides that have been prepared as single crystals by mild hydrothermal synthesis methods.

Crystal structure of dicaesium strontium hexa-cyanidoferrate(II), CsSr[Fe(CN)], from laboratory X-ray powder data.

Ferrocyanides with general formula [Fe(CN)], where and are cations, are thought to accept many substitutions on the and positions. In this communication, the synthesis and crystal structure of CsSr[Fe(CN)] are reported. The latter was obtained from KBa[Fe(CN)] particles, put in contact with caesium and strontium ions.

Crystal Growth of Alkali Uranyl Borates from Molten Salt Fluxes: Characterization and Ion Exchange Behavior of A(UO)BO (A = Cs, Rb, K).

A new family of layered alkali uranyl borates, A(UO)BO (A = Cs, Rb, K), was synthesized as high quality single crystals via high temperature flux growth methods. At room temperature, the compounds are structurally closely related although they crystallize in different monoclinic space groups, specifically 2/ (Cs), 2/ (Rb), and 2/ (K). At a low temperature (100 K), Cs(UO)BO becomes isostructural with K(UO)BO as the result of a reversible structure transition by Cs(UO)BO.

Galvanic Replacement-Driven Transformations of Atomically Intermixed Bimetallic Colloidal Nanocrystals: Effects of Compositional Stoichiometry and Structural Ordering.

Galvanic replacement reactions dictated by deliberately designed nanoparticulate templates have emerged as a robust and versatile approach that controllably transforms solid monometallic nanocrystals into a diverse set of architecturally more sophisticated multimetallic hollow nanostructures. The galvanic atomic exchange at the nanoparticle/liquid interfaces induces a series of intriguing structure-transforming processes that interplay over multiple time and length scales. Using colloidal Au-Cu alloy and intermetallic nanoparticles as structurally and compositionally fine-tunable bimetallic sacrificial templates, we show that atomically intermixed bimetallic nanocrystals undergo galvanic replacement-driven structural transformations remarkably more complicated than those of their monometallic counterparts.