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Nanocrystallite model for amorphous calcium carbonate
Author(s) -
Rez P.,
Sinha S.,
Gal A.
Publication year - 2014
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576714018202
Subject(s) - amorphous solid , amorphous calcium carbonate , diffraction , calcite , calcium carbonate , materials science , crystallography , birefringence , nanocrystal , x ray crystallography , optics , electron diffraction , mineralogy , analytical chemistry (journal) , chemistry , physics , nanotechnology , chromatography , composite material
Amorphous calcium carbonate phases, either synthesized artificially or generated biogenically, can be identified from broadened peaks in X‐ray or electron diffraction profiles. It is conceivable that randomly oriented nanocrystals, approximately 1 nm in size, could give rise to coherent diffraction profiles that are characterized as amorphous. The coherent diffraction profiles for 200 keV electrons, as might be used in an electron microscope, and Cu K α X‐rays were calculated for needle‐shaped calcite crystals bounded by facets and rhomb‐shaped crystals bounded by facets. Crystals of about 1.0 nm in size gave a profile that is consistent with the X‐ray measurements of amorphous calcium carbonate. The relative intensity of high‐angle broadened peaks and changes in the IR spectrum are best explained by disorder in the nanocrystallites. The presence of randomly oriented nanocrystallites also explains the lack of optical birefringence.