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

Abstract

A complete set of non-equivalent kinematic electron diffraction patterns corresponding 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 homologous 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 this set, specific electron diffraction patterns which allow an unequivocal identification of each phase can be sorted out. A systematic approach, based on the use of these calculated patterns, to make a reliable phase identification for any sample that contains a mixture of these phases is presented and applied to interpret different experimental electron diffraction patterns. The detailed interpretation of a number of experimental HREM images recorded on a sample of praseodymium oxide using a match with calculated images is also illustrated. These results and procedures provide supplementary confirmation of the fluorite-type module theory to explain the structural features of the higher rare earth oxide phases and provide the background necessary to characterize these materials reliably.