First natural hexaferrite with mixed β'''-ferrite (β-alumina) and magnetoplumbite structure from Jabel Harmun, Palestinian Autonomy
Ferrites of K and Ba close in composition to the known synthetic compounds KFe2+ 2Fe3+ 15 O25and BaMg2Fe3+ 16O27were found in a thin vein,filled with magnesioferrite and khesinite, in pyrometamorphic flamite–gehlenite hornfels of the Hatrurim Complex, Palestinian Autonomy. Both ferrites are characterized by a modular structure composed of 5-layered spinel (S) blocks interstratified with R-blocks. The R -modules of K-ferrite are of the β-alumina type whereas those in Ba-ferrite are of the magnetoplumbite type. Rare grains of K-Ba-ferrite of intermediate composition with the empirical crystal chemical formula (EPMA) (K0.57 Ba0.38 Na0.05)σ1 (Fe3+ 14.08 Mg1.42Al0.80 Zn0.59Ni0.16Ca0.14Cu0.09Mn0.03Ti0.03Si 0.02)σ17.36 O25.54, were also discovered. The structure of the natural mixed potassium-barium ferrite was investigated by single-crystal X-ray diffraction. The hexagonal space-group symmetry (P6 m 2,Z = 2) with a = 5.9137(2) and c = 33.1450(15) A is different to that (P 63/mmc) of the end-members and yields alternate stacking of β-alumina type KMg2 Fe15 O25 and magnetoplumbite type BaMg2 Fe16 O27 "supermodules", each extending ½ of the unit cell along c. Raman spectroscopic study confirms the mixed character of K-Ba-ferrite structure. K-Baferrite formed at non-equilibrium conditions and may be interpreted as an example of a nano-dissipative structure.
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Document Type: Research Article
Publication date: June 1, 2018
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