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New Aspects of U(V) Chemistry in Oxo-Materials: From Ambient to Extreme Conditions

This study explores the chemistry of U(V) in oxo-materials under both ambient and extreme conditions, investigating stabilization methods and properties. The research includes the substitution of aliovalent ions, magnetochemical analysis, and synthesis under high pressure/temperature conditions.

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New Aspects of U(V) Chemistry in Oxo-Materials: From Ambient to Extreme Conditions

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  1. NEW ASPECTS OF U(V) CHEMISTRY IN OXO-MATERIALS: FROM AMBIENT TO EXTREME CONDITIONS • Evgeny V. Alekseev 1,2 – Bin Xiao 1 – Philip Kegler 1– Piotr Kowalski 1–Sergey Novikov 3– Dirk Bosbach 1– Ivan Pidchenko4–Tonya Vitova4 – Thomas E. Albrecht-Schmitt5 - Kevin Huang6– Ryan Baumbach6 – Manfred Speldrich7 • 1Institut für Nukleare Entsorgung, Forschungszentrum Jülich, 52428 Jülich, Germany e-mail: e.alekseev@fz-juelich.de • 2Institut für Kristallographie, RWTH Aachen University, Jägerstraße 17-19 52066 Aachen, Germany • 3Samara State University, Akademik Pavlov Street 1, 443011 Samara, Russian Federation • 4 Institut für Nukleare Entsorgung, KIT, D-76344 Eggenstein-Leopoldshafen, Germany • 5 Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, Florida 32306, USA • 6 National Highmagneticfield laboratory,1800 E. Paul Dirac Dr. Tallahassee , Florida 32310, USA • 7 Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg1 D-52074 Aachen

  2. Introduction • Chemistry of actinides is of high interest due to their importance for nuclear industry and very interesting fundamental properties such as multivalence, multicoordination and complex magnetic properties • U is the most studied actinide element and can adopt oxidation states ranging from +2 to +6 • The chemistry of U in stable oxidation states +4 and +6 is well known • U(V)/U(III)/U(II) are exotic oxidation states and U(V) is only stable in solid state oxo-compounds • Mixed oxides with U(IV)/U(V) and U(V)/(VI) are well investigated, it is known that they may potentially form in nuclear fuel • The pure U(V) phases are very poorly investigated due to their narrow stability ranges

  3. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • Ca(UVIO2)W4O14, synthesized using (UO2)(NO3)4·6H2O, Ca(NO3)2, WO3 • Iriginite[a]-typed layer • Replace of Ca(NO3)2 with Ln2O3 (Ln = Nd-Tm and Y) can get isostructural compounds Ln(UVO2)W4O14 • [a]Krivovichev, et al; Can. Mineral. (2000). • In preparation • Ca2+ • Ln3+ • W blocks • Ln(UVO2)W4O14 • Ca(UVIO2)W4O14

  4. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • Replace of Ca(NO3)2 with Ln2O3 (Ln = Nd-Tm and Y) we can get isostructural compounds Ln(UVO2)W4O14 • After replacement, the distance of neighboring W blocks become larger, which forces the UO7 to deform. • Ca(UVIO2)W4O14 • U=O: 1.77 Å • Nd(UVO2)W4O14 • U=O: 1.91 Å • Local coordination geometry of UO7 • In preparation • W blocks • UO7

  5. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • Ln(UVO2)W4O14 (Ln = Nd, Sm, Eu, Gd, and Yb) • In preparation

  6. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • A: 3d3/2 → 5fδ/5fϕ • B: 3d3/2 → 5fπ • C: 3d3/2 → 5fσ • U M4-edge XANES spectrum • In preparation

  7. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • XPS result • Binding energies of U5+ peaks at 4f5/2 and 4f7/2 fit with those in KUVO3 and Ba2UV2O7 • Additional U6+ peaks are related to the surface oxidation of U5+ • with Dieter Schild from KIT • In preparation

  8. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • Ca(UVIO2)W4O14 • Ln(UVO2)W4O14 • Charge compensation mechanism • Ca2+ → Ln3+ + e- (1) • e- + U6+→ U5+ (2) • In preparation

  9. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • magnetochemicalanalysis of YUW4O16 and GdUW4O16 • with a new feature of the program CONDON 3.0 • U5+ • Ln3+ • U5+ • Ln3+ • U5+

  10. Ambient conditions:U(V) stabilization via aliovalent Ln to Ca substitution • In preparation

  11. Actinides chemistry under extreme conditions:how it can be made? • Combined multi anvil /piston cylinder press • Two well established high pressure / high temperature methods in one machine • Allows to apply hydrostatic pressures of up to 25 GPa and temperatures up to 2500°C • Large samples volumes of up to 800 mg • Performing experiments under high pressure / high temperature conditions allow a deep insight in the chemistry of actinides • Change of electron configuration (especially 5f electrons) • Change of coordination

  12. Actinides chemistry under extreme conditions:how it can be made? • Combined multi anvil /piston cylinder press • Piston cylinder module up to 1500°C and 4GPa

  13. Actinides chemistry under extreme conditions:how it can be made? • Combined multi anvil /piston cylinder press • Walker type multi anvil module up to 2500°C and 25GPa

  14. Actinides chemistry under extreme conditions:how it can be made? • Combined multi anvil /piston cylinder press • Walker type multi anvil module assembly

  15. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • The synthesis was performed at 10GPa and 1000°C in multi anvil press • We used UO3 and B2O3 as a flux • Very dense modification with a molecular volume dropped by ~ 30% (!) • Structurally more close to U(IV) oxides then to normal U(V) phases HP -U2O5 δ-U2O5 (ambient phase) • In preparation

  16. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • Bond distances and local coordination of U(V) centers in ambient and HP modifications HP -U2O5 UO8, UO9 and UO10 2.2Å – 2.8Å δ-U2O5 UO6 and UO7 1.91Å – 2.6Å • In preparation

  17. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • (a) The framework of HP-U2O5 shows a close similarity to UO2. (b) The idealized version of HP-U2O5 is identical to the fluorite-typed structure (UO2 adopts this structure type). This means the uranium cation sub-lattice in HP-U2O5 remains the same as that in the stoichiometric UO2. (c) Dismantle the framework into simpler layers shows that HP-U2O5 is based on two different fluorite-typed layers illustrated in (d) and (e), respectively.

  18. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • Formation procedures of HP-U2O5 from an initial fundamental building block (FBB) to the complex structure. (a) Thebutterfly-shapedFBB complex that is built of six tenfold face- and edge-sharing UO10 polyhedra. (b) The FBB is edge-linked with twelve UO4 cubes. (c) The resulting assemblage is further edge-linked with another eightFBBs, completing the three-dimensional fluorite-typed framework in (d).The appearance of extra bonding from edge-sharing manner inside the FBB indicates that the excessive oxygen anions do not incorporate into the fluorite structure individually, but rather participate in groups inside the

  19. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • Comparison of structural fragments observed in fluorite-typed U2O5 and U4O9 or U3O7. (a, c) The “butterfly-shaped” U6O36 fragment in U2O5. (b, d) The isolated cuboctahedron in U4O9or U3O7.

  20. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • For HP- U2O5 DFT+U lattice parameters are in good agreement with experiments • 1Brincat et al., Dalton Trans., 2015, 44, 2613 • P≈-ΔU/ΔV (ΔH=ΔU+PΔV, T = 0K) • Transition pressure (δ-U2O5 <−> HP-U2O5)is between 3 and 8 GPa • In preparation

  21. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • ΔU= Uδ-U2O5- UHP-U2O5 • DFT wrongly predicts HP-U2O5 to be stable even at ambient conditions! • DFT+U results show that electronic correlations stabilize δ-U2O5. • Recently developed DFT-based interaction potentials for U(V) species fail! → Collaboration with Imperial College London & LANL (Mike Cooper & Blas Uberuaga) to refit the potentials to our data! • In preparation

  22. Extreme conditions:U(V) stabilization via insitureducing of U(VI) • Molecular dynamics simulations of phase transition using refitted force-fields (EAM-type) δ-U2O5 HP-U2O5 An example of improvement of the modeling methods by benchmarking on the experimental data! • Codes used to perform the simulations: • Ab initio calculations: Quantum-ESPRESSO. • Force-fields molecular dynamics: LAMMPS. Studies performed in collaboration with: Mike Cooper & Blas Uberuaga (LANL) • In preparation

  23. Conclusions and Outlook • We demonstrated two ways for preparation of new U(V) oxo-phases • We demonstrated a possibility of U(V) stabilization in complex oxo-matrixes via Ln(III) cations incorporation into positions of 2+ cations • At the fist time we fully characterized the structure of HP-U2O5 • Using several analytical techniques we confirmed U(V) valence state in studied phases • Neutron diffraction experiments will be applied for study of magnetic ordering in 4fn-5f1 systems

  24. Thank you very much for your attention!

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