U_1.33T₄Al₈Si₂ (T = Ni, Co): Complex Uranium Silicides Grown from Aluminum/Gallium Flux Mixtures

Abstract

Two new quaternary analogs of the Gd1+x Fe4Si10‑y structure type were grown from the reaction of uranium, silicon, and a transition metal (nickel or cobalt) in an excess of aluminum/gallium flux. The use of a mixed flux was found to be necessary for the formation of U1.33T4Al8Si2 (T = Ni, Co). Single crystal X-ray diffraction data shows the presence of disordered U/Si layers that are characteristic of this structure type; precession photographs indicate partial formation of a superstructure and stacking disorder along the c-axis. This disorder may be the cause of the spin glass behavior that is particularly evident in the nickel analog, which exhibits a spin freezing transition at T F = 7 K. These compounds are resistant to chemical attack and oxidation and may be potential waste forms.

An1.33T4Al8Si2 (An = Ce, Th, U, Np; T = Ni, Co): Actinide Intermetallics with Disordered Gd1+xFe4Si10–y Structure Type Grown from Metal Flux

“…In the previous work, U 1.33 T 4 Al 8 Si 2 (T = Co, Ni) were synthesized by arc-melting uranium pieces, transition metal slugs, and silicon wafer pieces in a 0.5:1:1 U/T/Si mmol ratio. The arc-melted mixture was placed in an alumina crucible and was reacted with 10 mmol of aluminum and 10 mmol of gallium to form the products . However, Np and Pu metals are difficult to obtain, and arc-melting them has the potential to be hazardous; thus, the synthesis method was modified to use AnO 2 instead.…”

“…In previous work, two quaternary uranium intermetallic materials were synthesized by using Al/Ga flux. U 1.33 T 4 Al 8 Si 2 (T = Ni, Co) formed in the hexagonal Gd 1+ x Fe 4 Si 10– y structure type which exhibits a characteristic structural disorder in the uranium atom arrangement that leads to interesting magnetic phenomena such as fragile magnetic ordering and spin-glass-like behavior . In the current work, these studies were expanded to explore Ce, Th, and Np analogues of these phases.…”

Facile Oxide to Chalcogenide Conversion for Actinides Using the Boron–Chalcogen Mixture Method

“…Actinide chalcogenides adopt diverse structure types with distinct chemical compositions and specific actinide oxidation states, − which offer unique opportunities for studying 5f electron properties. − The synthesis of these materials can be achieved by a limited set of synthetic routes that include the traditional solid-state approach, − chemical vapor transport, − and the molten flux technique. − Regardless of the method chosen, there are two general actinide precursors that are consistently usedthe actinide metals and binary actinide chalcogenides. ,− One of the main obstacles faced when synthesizing the actinide chalcogenides are actinide oxide and oxychalcogenide impurities that often contaminate the resulting products and interfere with their property measurements. − Due to the high oxygen affinity of the actinides, even trace amounts of oxygen in the system will inevitably result in formation of these impurities. Although careful oxygen exclusion from the reaction media is an intuitive and straightforward approach for avoiding oxide impurities, it is unfortunately often nearly impossible to completely eliminate oxide contamination present in the reagents themselves. , This difficulty of needing to effectively deal with oxide or oxychalcogenide impurities in the starting materials motivated us to explore different synthetic approaches that would allow for the use of oxygen-contaminated reagents, or even oxides themselves, as the starting materials for the synthesis of oxygen-free actinide chalcogenides.…”

Structural Prediction and Overall Performances of CrSi2 Disilicides: DFT Investigations

“…Transition-metal (TM) disilicides are broadly applied for semiconductors, thermoelectric devices, high-temperature devices, and energy-storage systems. − Niobium-based disilicides are fascinating ultrahigh-temperature materials because they exhibit excellent high-temperature strength and good thermal stability . Molybdenum-based disilicides are regarded as the energy-storage materials because of their excellent electronic properties .…”