Refinement of the structure of (beta)-U4O9

(beta)-U4O9 is a superlattice structure based on the fluorite arrangement of UO2. The U atoms occupy positions close to those in UO2 and the additional O atoms are accommodated in cuboctahedral clusters of 43m symmetry, which are centred on the special 12-fold sites of the cubic space group I43d. The structure has been refined from single-crystal neutron data in accordance with the procedure described in the previous paper [Popa & Willis (2004). Acta Cryst. A60, 318-321 ].