R. Mauricot et al., CRYSTAL-STRUCTURE OF CE2O2.5S, AN OXIDIZED FORM OF CE2O2S, FROM NEUTRON AND X-RAY-POWDER DIFFRACTION, Zeitschrift fur Kristallographie, 212(1), 1997, pp. 24-28
The structure of Ce2O2.5S, a form of Ce2O2S oxidized by exposure to ai
r, was determined from combined X-ray and neutron powder diffraction d
ata. The phase retains the trigonal symmetry and the <P(3)over bar m1>
space group of the parent compound with cell parameters a = 3.96671(1
0) Angstrom and c = 6.8214(2) Angstrom and Z = 1. Refinements of 46 pa
rameters by the Rietveld method, using 80 (X-ray) and 138 (neutron) re
flections, led to R(p) = 0.102 and R(wp) = 0.129 (X-ray), R(p) = 0.063
and R(wp) = 0.048 (neutron), R(p) = 0.086 and R(wp) = 0.113 (global).
The oxidation process is shown to correspond to an insertion of oxyge
n anions in the hexagonal prismatic bipyramidal cavity of the host str
ucture. These additional oxygen atoms occupy a well defined off center
ed position of the cage, thereby forming: short Ce-O and O-O distances
. However. due to the disordered nature of the structure, no precise O
-O distances and therefore phase charge balance information have been
established.