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Backscattering; C (programming language); Calcium compounds; Crystal atomic structure; Crystal impurities; Electron diffraction; High resolution transmission electron microscopy; Silicon; Silicon compounds; Thermoanalysis; Atomic positions; Crystals structures; HRTEM images; Layered compound; Polytype transformations; Polytypes; Rapid cooling; Space Groups; Stackings; Zintl phase; Scanning electron microscopy
Abstract:
The Zintl phase CaSi2 is a layered compound with stacking variants known as 1P, 3R, and 6R. We extend the series by the 21R polytype formed by rapid cooling of the melt. The crystal structure of 21R-CaSi2 (space group R3̅m) was derived from HRTEM images, and the atomic positions were optimized by using the FPLO code (a = 3.868 Å, c = 107.276 Å). We explore polytype transformations by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and thermal analysis. While 6R-CaSi2 is thermodynamically stable at ambient conditions, nanosized impurities of silicon stabilize 3R-CaSi2 as a bulk phase. © 2024 The Authors. Published by American Chemical Society.
