Rare-earth oxides with fluorite-related structures: their systematic investigation using HREM images, image simulations and electron diffraction pattern simulations

A complete set of non-equivalent kinematic electron diffraction patterns co rresponding to the main zone axis orientations, [1 0 0](F), [1 1 0](F), [1 1 1](F) and [1 1 2](F) have been calculated for most members of the homolog ous series of binary anion-deficient, fluorite-related higher oxides of the rare earth elements, whose structures are currently resolved or postulated on the basis of the "fluorite-type module theory". From an analysis of thi s set, specific electron diffraction patterns which allow an unequivocal id entification of each phase can be sorted out. A systematic approach, based on the use of these calculated patterns, to make a reliable phase identific ation for any sample that contains a mixture of these phases is presented a nd applied to interpret different experimental electron diffraction pattern s. The detailed interpretation of a number of experimental HREM images reco rded on a sample of praseodymium oxide using a match with calculated images is also illustrated. These results and procedures provide supplementary co nfirmation of the fluorite-type module theory to explain the structural fea tures of the higher rare earth oxide phases and provide the background nece ssary to characterize these materials reliably. (C) 1999 Elsevier Science B .V. All rights reserved.