X-ray diffraction, Mössbauer spectroscopy, magnetic susceptibility, and specific heat investigations of Na4NpO5 and Na5NpO6

Anna L. Smith*, Amir Hen, Philippe E. Raison, Eric Colineau, Jean Christophe Griveau, Nicola Magnani, Jean Pierre Sanchez, Rudy J.M. Konings, Roberto Caciuffo, Anthony K. Cheetham

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

The hexavalent and heptavalent sodium neptunate compounds Na4NpO5 and Na5NpO6 have been investigated using X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, and specific heat measurements. Na4NpO5 has tetragonal symmetry in the space group I4/m, while Na5NpO6 adopts a monoclinic unit cell in the space group C2/m. Both structures have been refined for the first time using the Rietveld method. The valence states of neptunium in these two compounds, i.e., Np(VI) and Np(VII), respectively, have been confirmed by the isomer shift values of their Mössbauer spectra. The local structural properties obtained from the X-ray refinements have also been related to the quadrupole coupling constants and asymmetry parameters determined from the Mössbauer studies. The absence of magnetic ordering has been confirmed for Na4NpO5. However, specific heat measurements at low temperatures have suggested the existence of a Schottky-type anomaly at around 7 K in this Np(VI) phase.

Original languageAmerican English
Pages (from-to)4556-4564
Number of pages9
JournalInorganic Chemistry
Volume54
Issue number9
DOIs
StatePublished - 4 May 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

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