Lithium and Calcium Carbides with Polymeric Carbon Structures

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• 作者：Daryn Benson ; Yanling Li ; Wei Luo ; Rajeev Ahuja ; Gunnar Svensson ; Ulrich H盲ussermann
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：June 3, 2013
• 年：2013
• 卷：52
• 期：11
• 页码：6402-6406
• 全文大小：342K
• 年卷期：v.52,no.11(June 3, 2013)
• ISSN：1520-510X

文摘

We studied the binary carbide systems Li₂C₂ and CaC₂ at high pressure using an evolutionary and ab initio random structure search methodology for crystal structure prediction. At ambient pressure Li₂C₂ and CaC₂ represent salt-like acetylides consisting of C₂^{2鈥?/sup> dumbbell anions. The systems develop into semimetals (P3̅m1-Li₂C₂) and metals (Cmcm-Li₂C₂, Cmcm-CaC₂, and Immm-CaC₂) with polymeric anions (chains, layers, strands) at moderate pressures (below 20 GPa). Cmcm-CaC₂ is energetically closely competing with the ground state structure. Polyanionic forms of carbon stabilized by electrostatic interactions with surrounding cations add a new feature to carbon chemistry. Semimetallic P3̅m1-Li₂C₂ displays an electronic structure close to that of graphene. The 蟺* band, however, is hybridized with Li-sp states and changed into a bonding valence band. Metallic forms are predicted to be superconductors. Calculated critical temperatures may exceed 10 K for equilibrium volume structures.}