Brugman Sander J T, Ottenbros Anne B, Megens Frank, van Enckevort Willem J P, Vlieg Elias
Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands.
Cryst Growth Des. 2020 Jul 1;20(7):4802-4810. doi: 10.1021/acs.cgd.0c00578. Epub 2020 May 18.
The flatness of muscovite mica makes it a convenient substrate to study epitaxy. We have analyzed the growth of rhodochrosite (MnCO) crystals in solution and on muscovite mica. Growth at high supersaturations occurs via the formation of amorphous MnCO, which over time transforms into the crystalline form. In the presence of muscovite mica, epitaxial rhodochrosite crystals with a size of approximately 1 μm form. These crystals are kinetically roughened, because of the high supersaturation. The lattice match between MnCO and muscovite was found not to be the main reason for epitaxy. If the growth experiment is performed twice, the original epitaxial MnCO crystals are overgrown by many small crystallites. Similarly, spherical MnCO crystals with many overgrown facets can be formed on a muscovite surface that is exposed to humidity or by using a higher MnCO supersaturation. A comparison with calcite shows that epitaxy strongly depends on initial supersaturation for both carbonates. In contrast to previous studies, we find that at the right supersaturation, epitaxial calcite crystal growth is possible on freshly cleaved muscovite.
白云母的平整度使其成为研究外延的便利衬底。我们分析了菱锰矿（MnCO₃）晶体在溶液中和在白云母上的生长情况。在高过饱和度下的生长是通过无定形MnCO₃的形成进行的，随着时间的推移，无定形MnCO₃会转变成晶体形式。在白云母存在的情况下，会形成尺寸约为1μm的外延菱锰矿晶体。由于高过饱和度，这些晶体在动力学上变得粗糙。发现MnCO₃与白云母之间的晶格匹配不是外延的主要原因。如果生长实验重复进行两次，原来的外延MnCO₃晶体就会被许多小晶粒覆盖生长。类似地，在暴露于湿度的白云母表面上或通过使用更高的MnCO₃过饱和度，可以形成具有许多覆盖生长小面的球形MnCO₃晶体。与方解石的比较表明，两种碳酸盐的外延都强烈依赖于初始过饱和度。与先前的研究不同，我们发现，在合适的过饱和度下，外延方解石晶体可以在新劈开的白云母上生长。
