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A new mixed-valent iron ammonium phosphate, β-NH4Fe2(PO4)2, has been synthesized. The diffuse scattering observed on the diffraction patterns implies complex disorder phenomena and prevents a direct structure resolution. The latter can be solved by generating an artificially ordered orthorhombic structure, using a five-dimensional approach and performing partial integration of the diffuse streaks. In the artificially ordered structure, hexagonal tunnels, delimited by FeO6 octahedra, perpendicular to the directions [011] and [0\bar 11] can then be seen; they are filled either by [FeP2O10] zigzag ribbons or by NH_4^+ cations. It is shown that the disordering originates from the shifting of adjacent (100) tunnel slices of the structure with respect to each other along [011], allowing the formation of either new commensurate (superstructure) or incommensurate modulations, or even complete disorder along a. The close relationships with the ordered monoclinic form α-NH4Fe2(PO4)2 are also explained by this description.

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Crystallographic Information File (CIF)
Contains datablocks global, I


Structure factor file (CIF format)
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