Neutron diffraction studies of U4O9: comparison with EXAFS results

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• Previous X-ray absorption fine-structure (XAFS) studies suggested oxygen incorporation in U4O9 involves oxo groups and a mixed ordered/glassy uranium sublattice.
• These findings proposed short U-O bond distances (1.72-1.76 Å) in U4O9.

Purpose of the Study:

• To investigate the crystallographic structure of U4O9 using neutron diffraction.
• To challenge and verify the conclusions drawn from previous XAFS measurements regarding the structure of U4O9.

Main Methods:

• Powder neutron diffraction analysis of U4O9.
• Analysis of bond distances and crystallographic ordering.

Main Results:

• Neutron diffraction data indicate no U-O bonds shorter than 2.2 Å.
• The crystallographic structure of U4O9 is found to be fully ordered.
• No evidence supporting a 'spectroscopically silent' glassy portion of the uranium sublattice was observed.

Conclusions:

• The crystallographic structure of U4O9 is ordered, contradicting previous XAFS interpretations.
• The presence of oxo groups with short U-O bonds is not supported by neutron diffraction data.
• U4O9 does not exhibit a mixed ordered/glassy structure.