Studies of the crystal structure and crystal chemistry of titanomaghemite

Journal Article · · Am. Mineral.; (United States)

OSTI ID:5355341

Collyer, S; Grimes, N W; Vaughan, D J; Longworth, G

A natural single crystal of titanomaghemite from Pretoria, South Africa, containing 8.62 wt% Ti and 54.36 wt% Fe as determined by electron-microprobe analysis, has been studied by X-ray diffraction and Moessbauer spectroscopy. A crystal-structure parameter refinement of this titanomaghemite was undertaken, and values for the atom positions, anisotropic thermal parameters, and bond lengths are reported (R = 0.0235). The lattice is primitive cubic (a = 8.341(1)A) with space group P4/sub 3/32 (or the enantiomorphous P4/sub 1/32). Studies of this sample, and of two powder samples of synthetic end-member maghemite, using /sup 57/Fe Moessbauer spectroscopy at 300 K and 4.2 K and in a longitudinal applied magnetic field of 4.2 T, indicate that for the end-member ..gamma..-Fe/sub 2/O/sub 3/ samples, cation vacancies are restricted to octahedral sites. Combined single-crystal X-ray studies and Moessbauer spectroscopy of the titanomaghemite have given the following structural formula: Fe/sub 0.96//sup 3 +/()/sub 0.04/(Fe/sub 0.23//sup 2 +/Fe/sub 0.99//sup 3 +/Ti/sub 0.42//sup 4 +/()/sub 0.37/)O/sub 4//sup 2 -/, where () represents a cation vacancy. As the above formula shows, there are cation vacancies on both tetrahedral and octahedral sites in this titanomaghemite, the majority being on the octahedral sites. The authors believe the evidence of the Moessbauer spectra points to Fe/sup 2 +/ on the octahedral site. Moessbauer parameters are reported for the end-member ..gamma..-Fe/sub 2/O/sub 3/ samples and the titanomaghemite, and the cation and vacancy distributions on the sites in the latter are discussed in the light of previously published models

• Research Organization: Aston Univ., Birmingham (England)
• OSTI ID: 5355341
• Journal Information: Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 73:1-2; ISSN AMMIA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AFRICA
CHEMICAL ANALYSIS
COHERENT SCATTERING
CRYSTAL STRUCTURE
DIFFRACTION
ELECTRON MICROPROBE ANALYSIS
GEOLOGIC DEPOSITS
IRON COMPOUNDS
MICROANALYSIS
MOESSBAUER EFFECT
SCATTERING
SOUTH AFRICA
SPECTROSCOPY
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION