Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 56: Biomaterials
MM 56.3: Vortrag
Donnerstag, 29. März 2012, 16:15–16:30, H 0106
On the role of Mg atoms in calcite crystals: an ab initio study — •Pavlína Elstnerová1, Martin Friák1, Tilmann Hickel1, Helge Otto Fabritius1, Dierk Raabe1, Andreas Ziegler2, and Jörg Neugebauer1 — 1Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — 2University of Ulm, Ulm, Germany
Nearly 90% of animal species protect themselves with a cuticle: a complex hierarchical biocomposite often containing calcite that acts as a stiffening component. These calcite crystals contain impurities, commonly Mg or P, but the role of these elements is much debated. Here we present results of a parameter-free quantum-mechanical study of the thermodynamic, structural and elastic properties of single calcite crystals containing Mg atoms employing density functional theory (DFT). We calculated the electronic structure of bulk (CaxMgx−1)CO3 using 30-atomic supercells and studied the impact of Mg substitutions. Our calculations show that replacing Ca by Mg reduces the volume of substituted crystals and increases their bulk modulus as well as uniaxial and biaxial Young’s moduli. Our results thus indicate that the role of Mg in calcite crystals is to stiffen the material (for details see Elstnerová et al., Acta Biomater. 6 (2010) 4506). We also find significant Mg-induced local distortions of lattice geometries (involving carbonate groups) that are similar to those found at calcite surfaces.