Fan Changzeng, Li Jian
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P. R. China.
Phys Chem Chem Phys. 2015 May 21;17(19):12970-7. doi: 10.1039/c5cp00001g.
On the basis of the evolutionary methodology for crystal structure prediction, the potential crystal structures of magnesium carbide with a chemical composition of Mg2C are explored. Except the known cubic phase (Fm3̅m), two novel tetragonal structures (P42/mnm and I41/Amd) and two novel hexagonal structures (P63/mmc and P6̅M2) of Mg2C are found. All these four new phases are mechanically and dynamically stable by the calculated elastic constants and phonon dispersions. Furthermore, the effects of pressure and temperature on the phase transitions among different Mg2C polymorphs are investigated, implying that some new phases especially the P42/mnm phase may be synthesized in future. The ratio values of B/G are also calculated in order to analyze the brittle and ductile nature of these Mg2C phases. In addition, electronic structure calculations suggest that the I41/Amd phase is semimetallic and the other three new phases are all metallic, which is different from the previously proposed magnesium carbides. Meanwhile, the calculated electronic density maps reveal that strong ionic bonding exists between the Mg and C atoms.
基于晶体结构预测的演化方法，探索了化学组成为Mg2C的碳化镁的潜在晶体结构。除了已知的立方相（Fm3̅m）外，还发现了Mg2C的两种新型四方结构（P42/mnm和I41/Amd）和两种新型六方结构（P63/mmc和P6̅M2）。通过计算弹性常数和声子色散，所有这四个新相在力学和动力学上都是稳定的。此外，研究了压力和温度对不同Mg2C多晶型物之间相变的影响，这意味着未来可能会合成一些新相，特别是P42/mnm相。还计算了B/G的比值，以分析这些Mg2C相的脆性和韧性。此外，电子结构计算表明，I41/Amd相是半金属性的，而其他三个新相都是金属性的，这与先前提出的碳化镁不同。同时，计算得到的电子密度图表明，Mg和C原子之间存在强离子键。
