Structural investigation of Na₃NpO₄ and Na₃PuO₄ using X-ray diffraction and ²³⁷Np Mössbauer spectroscopy

Abstract

α-Na3NpO4 and α-Na3PuO4 exhibit an orthorhombic structure (Z = 8), in space group Fmmm, with lattice parameters a = 13.352(2) Å, b = 9.629(2) Å, and c = 6.673(2) Å for the neptunium compound, and a = 13.302(2) Å, b = 9.634(2) Å, and c = 6.651(2) Å for the plutonium analogue. The corresponding structure has been solved ab initio as no structural analogue could be found in the literature. The pentavalent state of neptunium has moreover been confirmed by (237)Np Mössbauer spectroscopy, and the local structural properties inferred from the X-ray Rietveld refinement have been related to the fitted quadrupole coupling constant and asymmetry parameters. The existence of a low temperature metastable m phase of Na3NpO4 and Na3PuO4, of the NaCl type, has also been suggested.

Structural Properties and Charge Distribution of the Sodium Uranium, Neptunium, and Plutonium Ternary Oxides: A Combined X-ray Diffraction and XANES Study

“…Pentavalent Na 3 NpO 4 and Na 3 PuO 4 are orthorhombic, in space group Fmmm. 26 The case of trisodium uranate Na 3 UO 4 is particularly complex 27 and not discussed further in the present work. We refer the reader to refs 26 and 27 for more detail on this particular composition.…”

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed “Breaks”?

“…Actinide–ligand bonding can be probed by a variety of spectroscopic tools, e.g., X-ray diffraction, − X-ray absorption, ,− Mössbauer spectroscopy, ,− or magnetic measurements. ,,− Quantum chemical calculations play a particularly important role in actinide chemistry research. From a theoretical viewpoint, an An complex is likely to exhibit a complicated multiconfigurational ground state (GS) because of the open 5f shell.…”

A New Look at the Structural and Magnetic Properties of Potassium Neptunate K2NpO4 Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity

“…The XANES spectrum of K 2 NpO 4 collected at the Np-L 3 edge is shown in Figure together with those of NpO 2 , Na 3 Np V O 4 , α-Na 2 Np VI O 4 , Na 4 Np VI O 5 , and Na 5 Np VII O 6 reference materials . The valence states of the sodium neptunates were confirmed by 237 Np Mössbauer spectroscopy from the values of their isomer shifts, − while the corresponding XANES spectra were reported in ref . The values of the measured inflection points and white lines are reported in Table .…”

“…10 The valence states of the sodium neptunates were confirmed by 237 Np Mössbauer spectroscopy from the values of their isomer shifts, 5−7 while the corresponding XANES spectra were reported in ref (10). The values of the measured inflection points and white lines are reported in Table 3.…”

“…A number of studies have recently been reported on several sodium actinide phases because of their relevance for the safety assessment of sodium-cooled fast reactors (SFRs). − Those studies have revealed intriguing magnetic properties for the α-Na 2 Np VI O 4 and Na 4 Np VI O 5 compositions and have stressed the need to re-evaluate the Np­(VI) crystal-field ground state.…”