Original paper

The crystal structure of SFCA-I, Ca3.18 Fe3+14.66Al1.34 Fe2+0.82O28, a homologue of the aenigmatite structure type, and new crystal structure refinements of ß-CFF, Ca2.99Fe3+14.30Fe2+0.55O25 and Mg-free SFCA, Ca2.45Fe3+9.04 Al1.74Fe2+0.16Si0.6O20

Mumme, W. G; Clout, J. M. F.; Gable, R. W.

Neues Jahrbuch für Mineralogie - Abhandlungen Band 173 Heft 1 (1998), p. 93 - 117

21 references

published: Mar 24, 1998

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ArtNo. ESP154017301005, Price: 29.00 €

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Abstract

Determination of the crystal structure of a new calcium ferrite has proved that it has M20O28 stoichiometry, Ca3.18(Fe3+14.66Al1.34) Fe2+0.82O28. The crystal structure shows that this ferrite is a higher homologue of previously studied SFCA (M14O20), together forming the first two members (n = 0,1) of the homologous series M14+6n O20+8n. Here designated SFCA-I, it has a triclinic cell with a = 10.43, b = 10.61, c = 11.84 Å,α (= 94.14, β = 111.35,γ = 110.27°. SFCA-I (n = 1) contains two types of alternating layers in its structure: the first is composed of octahedral walls that are each 6 octahedra wide; the second is a continuous layer composed of single ribbons of comer joined tetrahedra alternating with double ribbons of so-called "winged-octahedra". In SFCA (n = 0), the octahedral walls in the first type of layer are 4 octahedra wide, and the ribbons of "winged-octahedra" in the second type of layer are only one unit wide.

Keywords

Crystal