Nuclear-density distribution of ceria (CeO2, space group: Fm (3) over barm) has been investigated between 40 and 1497 degrees C by the maximum-entropy method (MEM) and MEM-based pattern fitting combined with the Rietveld method using neutron powder diffraction data. The refined unit-cell and atomic displacement parameters increased with an increase of temperature. The results of the MEM analysis reveal that the oxide ions have a positional disorder spreading over a wide area and shift to the < 111 > directions from the ideal position 8c 1/4,1/4,1/4 of the fluorite-type structure. The disorder of the oxide ions is more significant at higher temperatures and suggests the diffusion paths in the < 111 > and < 100 > directions. (c) 2005 Elsevier B.V. All rights reserved.