Study of Optical Vibrations Modes of Mineral Graphite by Micro Raman Spectroscopy
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Study of Optical Vibrations Modes of Mineral Graphite by Micro Raman Spectroscopy R. A. Silva-Molina1, R. Gámez-Corrales2*, J. M. Hernández-Cazares3 and I. G. EspinozaMaldonado3 1 Universidad Autónoma de San Luis Potosí, Doctorado Institucional de Ciencia e Ingeniería en Materiales, DICIM 78290, San Luis Potosí, S.L.P., México 2 Departamento de Física, Universidad de Sonora, Rosales y Blvd. Luis Encinas 78000, Hermosillo, Sonora, México. 3 Departamento de Geología, Universidad de Sonora, Rosales y Blvd Luis Encinas 78000, Hermosillo, Sonora, México. *E-mail: [email protected] ABSTRACT We present experimental and theoretical Raman spectra of natural graphite mineral of Sonora, Mexico. In this work, we take the advantage of the utility of the RAMAN spectroscopy as a technique to determine the crystallinity and structure of graphite mineral. The RAMAN spectroscopy provides information that can be used to determine the degree of graphitization, which in turn can be used to know the metamorphic degree of the host rock. The resulting RAMAN spectra of graphite were divided in first and second order regions, in the first region (1100-1800cm-1) the E2g vibration mode with D6h crystal symmetry occurs at 1580cm-1 (G band) that indicates poorly organized graphite, additional bands appears in the first order region at 1350 cm-1 (D band) called the defect band, and another at 1620 cm-1 (D* band). The secondorder region (2200-3400cm-1) shows several bands at ~2400 ~2700 ~2900 ~3300cm-1, all of them attributed to electron-phonon interactions or combination scattering. The density functional theory calculations were applied to determine the vibrational properties and the stacking layers of graphite. Keywords: Microstructure, Amorphous, Geologic, Raman Spectroscopy, electron-phonon interactions. INTRODUCTION The carbon atom has electronic configuration 1s22s22p2. In bigger structures, the 2s and 2p orbitals are disturbed by nearby atoms and they can form hybrids orbitals sp2 and sp3, the resulting orbitals allow up to four covalent bonds. The hybridized sp2 orbitals form three planar bonding with a 120° angle of separation between them. The atom of carbon linked to other carbon atoms in this configuration results in a hexagonal crystalline network infinitely wide and deep, with a dimensional thickness of an atom. Such a structure is called graphene; the simplest basic component of a graphite crystal is defined as a hexagonal graphene. Graphite is a 3D layering material formed by stacking single layers of sp2 carbon hexagonal networks. The carbon atoms show strong covalent bonding in a plane and weak van der Waals interactions between planes. The newly discoveries of new classes of nanomaterials such as fullerenes, carbon nanotubes and graphenes, have risen the scientific interest to the study graphite.
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In Mexico, Sonora is the third state, after Coahuila and Oaxaca for the occurrence of coal and graphite deposits [1]. Although the graphite production in Sonora date back since 19th century, very little is known about
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