Infrared spectroscopic properties of goethite: anharmonic broadening, long-range electrostatic effects and Al substitution

Blanchard, Marc and Balan, Etienne and Giura, Paola and Béneut, Keevin and Yi, Haohao and Morin, Guillaume and Pinilla, Carlos and Lazzeri, Michele and Floris, Andrea (2014) Infrared spectroscopic properties of goethite: anharmonic broadening, long-range electrostatic effects and Al substitution. Physics and Chemistry of Minerals, 41 (4). pp. 289-302. ISSN 0342-1791

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Abstract

The infrared spectrum and its temperature dependence (20–320 K) were collected on a synthetic goethite sample (α-FeOOH). In addition, the infrared powder absorption spectrum of goethite and aluminum-substituted goethite was computed using ab initio quantum mechanical calculations based on density functional theory. This combined experimental and theoretical approach allows (1) the unequivocal assignment of absorption bands to the corresponding vibrational modes, (2) separate identification of the effects of the particle shape and of the aluminum substitution on the infrared spectrum, and (3) a discussion of the anharmonic properties and the origin of the line broadening in goethite. In particular, the two well-resolved OH bending absorption bands show different temperature evolution. Their detailed analysis suggests that the broadening of the band at ~800 cm−1 cannot be described solely by a usual three-phonon process. The strong anharmonic behavior of this mode implies the addition of a four-phonon process, such as a pure dephasing process. In our calculations, the effect of the Hubbard U correction is also investigated and found to be most visible on the OH stretching and bending modes, in relation to the associated structural relaxation. The OH stretching frequencies decrease, leading to a better agreement with experimental frequencies, while the OH bending frequencies increase.

Keywords:Goethite, Aluminum substitution, Density functional theory, Infrared spectroscopy, JCNotOpen
Subjects:F Physical Sciences > F690 Geology not elsewhere classified
Divisions:College of Science > School of Mathematics and Physics
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ID Code:22792
Deposited On:02 Jun 2016 10:41

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