Experimental Evidence of Static Disorder of Carbonate Ions in Ba-Doped Calcite
42 Pages Posted: 29 Mar 2022
Abstract
Incorporation of structurally incompatible Ba2+ into calcite by crystallization via amorphous calcium carbonate induces the extinction of 113 reflection in the X-ray diffraction patterns even at room temperature. It has recently been hypothesized that this phenomenon is caused by the static disorder of CO32– in Ba-doped calcite exhibiting notable increase in the unit-cell volume. To experimentally clarify this hypothesis, we investigated the behavior of CO32– and the local structure in Ba-doped calcite samples. Powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements indicated that CO32– ions in Ba-doped calcite were disordered even at low temperatures down to 91K. 13C MAS NMR spectra suggest that Ba atoms in calcite are randomly substituted for Ca atoms. The Ca K-edge XAFS and the IR absorption spectra indicated the symmetry reduction of CO32– with increasing Ba content. These changes in the local structure by incorporating incompatible Ba2+ into calcite cause the static disorder of CO32– at room temperature.
Keywords: static disorder, calcite, barium, amorphous calcium carbonate
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