Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 98-106).

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: Robert W. Birkmire, Dept. of Materials Science & Engineering. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [128]-134).

Thesis (M.S.)--University of Nevada, Reno, 2008. / "August 2008." Includes bibliographical references (leaves 72-82). Online version available on the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Food Science." Includes bibliographical references.

abstract: Many species e.g. sea urchin form amorphous calcium carbonate (ACC) precursor phases that subsequently transform into crystalline CaCO3. It is certainly possible that the biogenic ACC might have more than 10 wt% Mg and ∼ 3 wt% of water. The structure of ACC and the mechanisms by which it transforms to crystalline phase are still poorly understood. In this dissertation our goal is to determine an atomic structure model that is consistent with diffraction and IR measurements of ACC. For this purpose a calcite supercell with 24 formula units, containing 120 atoms, was constructed. Various configurations with substitution of Ca by 6 Mg ions (6 wt.%) and insertion of 3-5 H2O molecules (2.25-3.75 wt.%) in the interstitial positions of the supercell, were relaxed using a robust density function code VASP. The most noticeable effects were the tilts of CO3 groups and the distortion of Ca sub-lattice, especially in the hydrated case. The distributions of Ca-Ca nearest neighbor distance and CO3 tilts were extracted from various configurations. The same methods were also applied to aragonite. Sampling from the calculated distortion distributions, we built models for amorphous calcite/aragonite of size ∼ 1700 nm3 based on a multi-scale modeling scheme. We used these models to generate diffraction patterns and profiles with our diffraction code. We found that the induced distortions were not enough to generate a diffraction profile typical of an amorphous material. We then studied the diffraction profiles from several nano-crystallites as recent studies suggest that ACC might be a random array of nanocryatallites. It was found that the generated diffraction profile from a nano-crystallite of size ∼ 2 nm3 is similar to that from the ACC. / Dissertation/Thesis / Ph.D. Physics 2012

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