High-resolution structural study of zinc ion incorporation at the calcite cleavage surface

The atomic-scale structure of Zn2+ incorporated at the CaCO3 (10 (1) over bar 4) surface by adsorption from solution was determined by X-ray standing wave triangulation and surface extended X-ray absorption fine structure spectroscopy. At low coverage (approximately 0.1 ML), Zn2+ substitutes for Ca2+ in the surface layer. Structural relaxation of the adjacent in-plane CO32- ions in the host surface is shown by the reduced nearest-neighbor distance of Zn-O relative to Ca-O. Relaxation of the Zn2+ ion in the out-of-plane direction is shown by the displacement of its lattice position from the ideal Ca2+ position. These relaxations, resulting in a local lattice buckling feature at the Zn2+ adsorption site, can be fully explained as the combined effect of the electrostatic relaxation of the nearest-neighbor anions in response to the smaller size of Zn2+, and the bonding asymmetry due to surface truncation. (C) 1998 Published by Elsevier Science B.V. All rights reserved.