The structure of Na2UCl6 and Li2UCl6 from multiphase powder neutron profile refinement

Abstract

The structures of Na2UCl6 and Li2UCl6 have been determined by powder neutron diffraction at room temperature in the presence of NaCl and LiCl respectively as impurity. Na2UCl6crystallizes in space group P{\bar 3}m1, with a = 11 8062(9), c = 6.3243(2) Å, and Z = 3. The best description of Li2UCl6 was found in space group P63/mmc, a = 11.1915(5), c = 6.0356(1) Å, and Z = 3, with uranium and lithium ions disordered over the available octahedral sites. The results give the first illustration of the relative ease of analysing a two-phase mixture using a Rietveld profile program adapted to refine simultaneously more than one phase.