Abakumov, Artem M.

Bourgeois, J.

et al.

Hervieu, M.

Poienar, M.

Van Tendeloo, Gustaaf

Abstract: A polycrystalline sample of LuFe2O4 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with M\uf6ssbauer spectroscopy and transport and magnetic properties. A monoclinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoclinic C2/m space group [aM = 5.9563(1)\u2009\uc5, bM = 3.4372(1)\u2009\uc5, cM = 8.6431(1)\u2009\uc5, \u3b2 = 103.24(1)\ub0]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector q\u20d71 = \u3b11a\u20d7M* + \u3b31c\u20d7M* (with \u3b11  45 0.55, \u3b31  45 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with q\u20d71 vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark field scanning TEM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the O4 stoichiometry

Evidence of oxygen-dependent modulation in <tex>LuFe_{2}O_{4}$</tex>

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