Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 23: Poster session

MM 23.6: Poster

Tuesday, February 26, 2008, 14:45–18:00, Poster B

Stability, electronic and magnetic properties of iron oxyhydroxides under high pressure: Insights from first principles — •Katrin Otte¹, Rossitza Pentcheva¹, and Jim Rustad² — ¹Section Crystallography, Dept. for Earth and Environmental Sciences, University of Munich — ²Department of Geology, UC Davis

Iron oxyhydroxides (FeOOH) play an important role in nature and technology, e.g. in binding heavy metals. The high pressure behavior of water containing minerals is important for understanding the processes in the Earth’s crust and lower mantle. Using density functional theory (DFT), we investigate the structural, electronic and magnetic properties of the iron oxyhydroxide-polymorphs (α-, β-, γ- and hp-FeOOH) under high pressures. We find that under ambient conditions goethite (α) is the lowest energy phase, while at high pressures the hp-phase becomes more favorable. The relative stability of the different phases follows the trend obtained from recent calorimetric measurements [1]. Bond lengths are in a good agreement with available experimental data. While in the ground state Fe³⁺-ions are coupled antiferromagnetically, at high pressures a transition to a ferromagnetic alignment takes place in hp-FeOOH. At ambient conditions all AFM phases are insulating within the generalized gradient approximation (GGA). However, a substantial improvement of the size of the band gap is achieved by including electronic correlations within the LDA+U method.

[1] C. Laberty and A. Navrotsky, Geochimica et Cosmochimica Acta 62, 2905-2913 (1998)