title: Anisotropic lattice distortions in biogenic aragonite.
abstract: Composite biogenic materials produced by organisms have a complicated design on a nanometre scale. An outstanding example of organic-inorganic composites is provided by mollusc seashells, whose superior mechanical properties are due to their multi-level crystalline hierarchy and the presence of a small amount (0.1-5 wt%) of organic molecules. The presence of organic molecules, among other characteristics, can influence the coherence length for X-ray scattering in biogenic crystals. Here we show the results of synchrotron high-resolution X-ray powder diffraction measurements in biogenic and non-biogenic (geological) aragonite crystals. On applying the Rietveld refinement procedure to the high-resolution diffraction spectra, we were able to extract the aragonite lattice parameters with an accuracy of 10 p.p.m. As a result, we found anisotropic lattice distortions in biogenic aragonite relative to the geological sample, maximum distortion being 0.1% along the c axis of the orthorhombic unit cell. The organic molecules could be a source of these structural distortions in biogenic crystals. This finding may be important to the general understanding of the biomineralization process and the development of bio-inspired 'smart' materials.
authors.affiliation: Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel. bpokroy@tx.technion.ac.il
authors.forename: Boaz
authors.initials: B
authors.lastname: Pokroy
authors.forename: John P
authors.initials: JP
authors.lastname: Quintana
authors.forename: El'ad N
authors.initials: EN
authors.lastname: Caspi
authors.forename: Alex
authors.initials: A
authors.lastname: Berner
authors.forename: Emil
authors.initials: E
authors.lastname: Zolotoyabko
mesh_terms: D000818:Animals; D016880:Anisotropy; D001672:Biocompatible Materials / Q000737:chemistry; D002119:Calcium Carbonate / Q000032:analysis* / Q000737:chemistry* / Q000145:classification; D019015:Geologic Sediments / Q000032:analysis / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D008974:Mollusca / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D002119:Calcium Carbonate