title: The incommensurately modulated structures of the perovskites NaCeMnWO6 and NaPrMnWO6.
abstract: The structures of the doubly ordered perovskites NaCeMnWO(6) and NaPrMnWO(6), with rock salt ordering of the Mn(2+) and W(6+)B-site cations and layered ordering of the Na(+) and (Ce(3+)/Pr(3+)) A-site cations, have been studied by transmission electron microscopy, electron diffraction, neutron and synchrotron X-ray powder diffraction. Both compounds possess incommensurately modulated crystal structures. In NaCeMnWO(6) the modulation vector (with reference to the ideal ABX(3) perovskite subcell) is q ≈ 0.067a* (∼58.7 Å) and in NaPrMnWO(6)q ≈ 0.046a* (∼85.3 Å). In both compounds the superstructures are primarily the two-dimensional chessboard type, although some crystals of NaCeMnWO(6) were found with one-dimensional stripes. In some crystals of NaPrMnWO(6) there is a coexistence of chessboards and stripes. Modeling of neutron diffraction data shows that octahedral tilting plays an important role in the structural modulation.
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, Madrid 28040, Spain.
authors.forename: Susana
authors.initials: S
authors.lastname: García-Martín
authors.forename: Graham
authors.initials: G
authors.lastname: King
authors.forename: Gwilherm
authors.initials: G
authors.lastname: Nénert
authors.forename: C
authors.initials: C
authors.lastname: Ritter
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Woodward