ISSN:
1432-2021
Keywords:
Key words Barbosalite
;
Iron phosphate
;
Structure refinement
;
Mössbauer spectroscopy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Abstract Natural barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 from Bull Moose Mine, South Dakota, U.S.A., having ideal composition, was investigated with single crystal X-ray diffraction techniques, Mössbauer spectroscopy and SQUID magnetometry to redetermine crystal structure, valence state of iron and evolution of 57Fe Mössbauer parameter and to propose the magnetic structure at low temperatures. At 298 K the title compound is monoclinic, space group P21/n, a o = 7.3294(16) Å, b o = 7.4921(17) Å, c o = 7.4148 (18) Å, β = 118.43(3)°, Z = 2. No crystallographic phase transition was observed between 298 K and 110 K. Slight discontinuities in the temperature dependence of lattice parameters and bond angles in the range between 150 K and 180 K are ascribed to the magnetic phase transition of the title compound. At 298 K the Mössbauer spectrum of the barbosalite shows two paramagnetic components, typical for Fe2+ and Fe3+ in octahedral coordination; the area ratio Fe3+/Fe2+ is exactly two, corresponding to the ideal value. Both the Fe2+ and the Fe3+ sublattice order magnetically below 173 K and exhibit a fully developed magnetic pattern at 160 K. The electric field gradient at the Fe2+ site is distorted from axial symmetry with the direction of the magnetic field nearly perpendicular to Vzz, the main component of the electric field gradient. The temperature dependent magnetic susceptibility exhibits strong antiferromagnetic ordering within the corner-sharing Fe3+-chains parallel to [101], whereas ferromagnetic coupling is assumed within the face-sharing [1 1 0] and [−1 1 0] Fe3+-Fe2+-Fe3+ trimer, connecting the Fe3+-chains to each other.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002699900078
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