Iron oxide compounds in 12 selected Canadian soil samples have been characterized by Mössbauer, X-ray, chemical, infrared absorption, and differential thermal methods. Chemical differentiation provides useful information about the forms of iron compounds present such as crystalline, amorphous, inorganic, and organic complexed iron compounds. X-ray diffraction methods can generally identify mineral species of crystalline iron compounds. However, detection limits of goethite and hematite, which are iron oxide minerals commonly present in soils, are about 7% and 10%, respectively. The Mössbauer method is especially useful for identification of small amounts of these iron oxide compounds which are far beyond X-ray detection limits. In addition, information about grain size of hematite and goethite, the Fe3+/Fe2+ ratio and characterization of the 'amorphous' fraction are also available from Mössbauer spectra. Infrared absorption and differential thermal analyses provide supplementary data concerning organic complexed iron compounds.Hematite content in the soils examined is always lower than 10%, but goethite content varies widely and coexistence of both minerals appears to be common.
R6sum6.-Nous donnons ici les resultats d'un travail de recherche sur des monocristaux de Feo.p96S, comprenant des analyses de susceptibilite magnetique, de spectromttrie Mossbauer, de conductivite electrique, de puissance thermotlectrique et de DTA. La conductivite electrique montre a T, (-420 K) une augmentation d'un facteur de-102 dans les deux directions Ctudites soit parallkle et perpendiculaire B l'axe-c. A basse temperature le deplacement isomerique correspond B celui d'une substance non metallique mais sa variation en fonction de la temperature semble anormale. La separation quadrupolaire donne une indication sur la structure de bande dans la phase 2C (basse temperature). Les donnkes Mossbauer concernant le champ magnktique interne en plus des resultats de susceptibilite magndtique suggkrent que le moment magndtique ne change pas appreciablement B T,. La temperature de Debye, calculee a partir des fractions Mossbauer, tombant de f a~o n importante a la transition, indique une contribution du rCseau a l'entropie de transition. En conclusion, le FeS est un semiconducteur antiferromagnktique a spin localise et A bande interdite dtroite sous T, et un metal antiferromagnktique B spin localise non typique au-dessus de T,. Si l'augmentation de la conductivitk B T, est due B la delocalisation du 6e Clectron a spin P, l'electron itinkrant semble conserver un moment.
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