Knapp M, Ruschewitz U
Technische Universität Darmstadt, Institut für Materialwissenschaft, Germany.
Chemistry. 2001;7(4):874-80. doi: 10.1002/1521-3765(20010216)7:4<874::aid-chem874>3.0.co;2-v.
Pure CaC2, free of CaO impurities, was obtained by the reaction of elemental calcium with graphite at 1,070 K. By means of laboratory X-ray and synchrotron powder diffraction experiments, the phase diagram was investigated in the temperature range from 10 K to 823 K; this confirmed the literature data that reported the partial coexistence of up to four modifications. Aside from a cubic high-temperature modification CaC2 IV (Fm3m, Z = 4) and the well-known tetragonal modification CaC2 I (I4/mmm, Z = 2), a low-temperature modification CaC2 II (C2/c, Z =4) that crystallizes in the ThC2 structure type and a metastable modification CaC2 III (C2/m, Z = 4) that crystallizes in a new structure type were found. It was shown that phase transition temperatures as well as the relative amounts of the various CaC2 modifications depend upon the size of the crystallites, the thermal treatment. and the purity of the sample, as a comparison with technical CaC2 confirmed.
通过元素钙与石墨在1070K下反应制得不含CaO杂质的纯CaC₂。借助实验室X射线和同步加速器粉末衍射实验，在10K至823K温度范围内研究了相图；这证实了文献数据，即报道了多达四种变体的部分共存情况。除了立方高温变体CaC₂ IV（Fm3m，Z = 4）和著名的四方变体CaC₂ I（I4/mmm，Z = 2）外，还发现了在ThC₂结构类型中结晶的低温变体CaC₂ II（C2/c，Z = 4）和在新结构类型中结晶的亚稳变体CaC₂ III（C2/m，Z = 4）。结果表明，相变温度以及各种CaC₂变体的相对含量取决于微晶尺寸、热处理和样品纯度，与工业CaC₂的比较证实了这一点。
