1 / 28

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.

rbouknight
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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!

More Related