MS14-P04 Atomic Displacements in Yttrium-Manganese-Oxide with and without Fe-substitution, revealed by Resonant X-ray DiffractionYttrium-Manganese-Oxide YMn2O5 (YMO) is studied since 1973 due to its remarkable magnetic properties, e. g. different modulation phenomena and several respective phase transitions. The ambient temperature phase of YMO is paraelectric and paramagnetic. The lattice has the orthorhombic space group Pbam (55) and its building units are [MnO5] pyramides and [MnO6] octahedra, the latter forming chains along the c direction. At 45 K, 40 K, 39 K and 19 K, the structure changes between several magnetic modulations . Here, we are interested in the commensurate modulated phase between 39 K and 19 K. Presumably within space group Pb21m (26), the respective lattice modulation vector is 0 0 ½, whereas the polarization points along b. However, crystal structure refinements in a non-centrosymmetric space group showing polar displacements have not yet been successful. Moreover, there is still disagreement about the interplay of magnetic superstructure and a polar displacement pattern. To analyze possible displacements of the commensurate phase in detail, we apply the newly developed and highly sensitive Resonant X-ray Diffraction (RXD) Method REXSuppress that uses destructive interference of the intensity at carefully chosen Bragg reflections . For this structure analysis, we determined atomic displacement parameters (ADP) of the high and low temperature phase with the same method and surveyed the appearance of superstructure reflections that would accompany the transition to space group Pb21m (26).
Additionally, we examined the distribution of Fe in Yttrium-Manganese-Iron-Oxide (YMnFeO5), which results from the substitution of 50% Mn. The element- and site-selectivity of RXD is capable of separating the two distinct Mn Wyckoff sites (pyramide and octahedron), in particular with the octahedral site possessing forbidden reflections (reflection condition hkl with h + k = 2n). Thus, the question of occupation is easily accessible and will be treated similar as by .References:
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 F. Winderlich et al., Phys. Rev. B 82(1) 014409 (2010).Keywords: refinement, mullite, commensurate