Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
Science. 2013 Apr 26;340(6131):454-7. doi: 10.1126/science.1232139.
Calcite, aragonite, and vaterite are the three anhydrous polymorphs of calcium carbonate, in order of decreasing thermodynamic stability. Although vaterite is not commonly found in geological settings, it is an important precursor in several carbonate-forming systems and can be found in biological settings. Because of difficulties in obtaining large, pure, single crystals, the crystal structure of vaterite has been elusive for almost a century. Using aberration-corrected high-resolution transmission electron microscopy, we found that vaterite is actually composed of at least two different crystallographic structures that coexist within a pseudo-single crystal. The major structure exhibits hexagonal symmetry; the minor structure, existing as nanodomains within the major matrix, is still unknown.
方解石、文石和球霰石是碳酸钙的三种无水多晶型物，其热力学稳定性依次降低。尽管球霰石在地质环境中并不常见，但它是几种碳酸盐形成体系中的重要前体，并且可以在生物环境中找到。由于难以获得大尺寸、纯净、单晶，球霰石的晶体结构近一个世纪以来一直难以确定。使用像差校正的高分辨率透射电子显微镜，我们发现球霰石实际上由至少两种不同的晶体结构组成，它们在准单晶内共存。主要结构呈现六方对称性；次要结构，以纳米域的形式存在于主要基质中，其结构仍不清楚。
