Structural investigation of Na$_3$NpO$_4$ and Na$_3$PuO$_4$ using X-ray diffraction and $^{237}$Np Mossbauer spectroscopy

Abstract : $\alpha$Na$_3$NpO$_4$ and $\alpha$Na$_3$PuO$_4$ exhibit an orthorhombic structure (Z = 8), in space group $Fmmm$, with lattice parameters $a$ = 13.352(2) $\mathring{A}$, b = 9.629(2) $\mathring{A}$, and c = 6.673(2) $\mathring{A}$ for the neptunium compound, and a = 13.302(2) angstrom, b = 9.634(2) angstrom, and c = 6.651(2) angstrom 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 Mssbauer 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 Na$_3$NpO$_4$ and Na$_3$PuO$_4$, of the NaCl type, has also been suggested.
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Submitted on : Wednesday, March 28, 2018 - 10:57:26 AM
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A. L. Smith, P. E. Raison, A. Hen, D. Bykov, Eric Colineau, et al.. Structural investigation of Na$_3$NpO$_4$ and Na$_3$PuO$_4$ using X-ray diffraction and $^{237}$Np Mossbauer spectroscopy. Dalton Transactions, Royal Society of Chemistry, 2015, 44, pp.18370-18377. ⟨10.1039/c5dt02168e⟩. ⟨cea-01745406⟩

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