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Delafossite structure of heterogenite polytypes (HCoO2) by Raman and infrared micro-spectroscopy.

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Title: Delafossite structure of heterogenite polytypes (HCoO2) by Raman and infrared micro-spectroscopy.
Authors: Burlet, C.1 christian.burlet@naturalsciences.be, Goethals, H.1, Vanbrabant, Y.1
Source: Spectrochimica Acta Part A: Molecular & Biomolecular Spectroscopy. Apr2016, Vol. 159, p90-97. 8p.
Subjects: Molecular structure, Infrared spectroscopy, Mineralogy, Crystal structure, Cobalt hydroxides
Abstract: Heterogenite is commonly referred in mineralogy literature as a cobalt oxy-hydroxide CoO(OH). However, detailed analysis of Raman and infrared spectra acquired on particularly well-crystallized natural samples of heterogenite suggests that the mineral can be characterized by a delafossite-type structure, with a general chemical formula ABO 2 . Indeed, the Raman spectrum of heterogenite, along the one with grimaldiite (HCrO 2 ), lacks visible free OH-group vibrational modes, while the infrared spectrum shows strong hydrogen bond absorption bands. HCoO 2 is thus a better formulation of heterogenite that describes more clearly its vibrational behavior and avoids the confusion in literature. Electronic backscattered diffraction (EBSD) is then used to distinguish and map the 2H and 3R heterogenite natural polytypes for the first time. The comparison of EBSD and Raman mappings clearly indicates that the 2H polytype is characterized by an additional peak at 1220 cm − 1 . The presence/absence is therefore an efficient tool to distinguish both polytypes. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:Heterogenite is commonly referred in mineralogy literature as a cobalt oxy-hydroxide CoO(OH). However, detailed analysis of Raman and infrared spectra acquired on particularly well-crystallized natural samples of heterogenite suggests that the mineral can be characterized by a delafossite-type structure, with a general chemical formula ABO 2 . Indeed, the Raman spectrum of heterogenite, along the one with grimaldiite (HCrO 2 ), lacks visible free OH-group vibrational modes, while the infrared spectrum shows strong hydrogen bond absorption bands. HCoO 2 is thus a better formulation of heterogenite that describes more clearly its vibrational behavior and avoids the confusion in literature. Electronic backscattered diffraction (EBSD) is then used to distinguish and map the 2H and 3R heterogenite natural polytypes for the first time. The comparison of EBSD and Raman mappings clearly indicates that the 2H polytype is characterized by an additional peak at 1220 cm − 1 . The presence/absence is therefore an efficient tool to distinguish both polytypes. [ABSTRACT FROM AUTHOR]
ISSN:13861425
DOI:10.1016/j.saa.2016.01.038