Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure

Nylén, Johanna; Konar, Sumit; Lazor, Peter; Benson, Daryn; Häußermann, Ulrich

doi:10.1063/1.4770268

Cited by 38 publications

(38 citation statements)

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“…1940 cm -1 and 2060 cm -1 (Fig.3a). Nylén et al 23 reported that the C≡C stretching of Li 2 C 2 is at 1872 cm -1 in the Raman spectrum. We confirmed this with the Raman spectrum of our home-prepared Li 2 C 2 ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Reversible reduction of Li₂CO₃

et al. 2015

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ARTICLE This journal isLithium carbonate (Li 2 CO 3 ), either as a product of the conversion reaction or as an important component of the solid-electrolyte interphase (SEI) layer on the anode of a lithium ion (Li-ion) battery, is known to be chemically inactive in both reducing and oxidizing atmospheres. No sufficient evidence was shown that Li 2 CO 3 can be reduced, let alone to recognize its reduction products. Here we clarify that Li 2 CO 3 , as a product of conversion reaction of cobalt carbonate (CoCO 3 ) upon Li insertion, can indeed be further reduced/converted to lithium carbide (Li 2 C 2 ) and lithium oxide (Li 2 O), based on spectroscopic and transmission electron microscopic analyses. These findings will have important guidance to designing electrode (materials) with more stable cycling performances, finding ways to convert some inert compounds to useful electrode materials, and search for electrode materials with higher specific capacities, as well as in understanding the excess reversible capacity of some electrode reactions.

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Section: Resultsmentioning

confidence: 99%

Reversible reduction of Li₂CO₃

et al. 2015

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“…The multielement cases are needed to understand the feature of antimetallization from a different perspective at the fundamental level. For this purpose, the compounds of C m Li n are considered to be good examples for the understanding of the nature of physics (12)(13)(14). Examining their high-pressure behavior and exploring the possible metallization and superconductivity in this system are the focus of this work.…”

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confidence: 99%

Crossover from metal to insulator in dense lithium-rich compound CLi ₄

Jin

Chen

Cui

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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At room environment, all materials can be classified as insulators or metals or in-between semiconductors, by judging whether they are capable of conducting the flow of electrons. One can expect an insulator to convert into a metal and to remain in this state upon further compression, i.e., pressure-induced metallization. Some exceptions were reported recently in elementary metals such as all of the alkali metals and heavy alkaline earth metals (Ca, Sr, and Ba).Here we show that a compound of CLi 4 becomes progressively less conductive and eventually insulating upon compression based on ab initio density-functional theory calculations. An unusual path with pressure is found for the phase transition from metal to semimetal, to semiconductor, and eventually to insulator. The Fermi surface filling parameter is used to describe such an antimetallization process.high pressure | antimetallization | lithium-rich compound S imilar to the same first group element, hydrogen, lithium with a single valence electron is a good conductor of heat and metal at ambient conditions. It can transform from a nearly freeelectron metallic solid to an insulating one, i.e., pressure-induced antimetallization (1-4). As a contrasting counterpart, lithium often provides a meaningful referential aspect for understanding hydrogen at high pressures (5). Hydrogen-rich materials of group-IV hydrides (6-10) are believed to be good candidates for the realization of metallization and even superconductivity at modest pressures much lower than that required for pure hydrogen due to "chemical precompression." Whether group-IV lithium compounds hold similar expected outstanding properties to those of their same group hydrides becomes an interesting topic.On the other hand, high-pressure studies delivered a completely unexpected antimetallization behavior for alkali metals such as Li (1, 3, 4) and Na (11). Charge transition from 2s to 2p of Li or Na itself was proposed to account for such a behavior. Being restricted to the pure elements in these cases, some underlying properties are covered. The multielement cases are needed to understand the feature of antimetallization from a different perspective at the fundamental level. For this purpose, the compounds of C m Li n are considered to be good examples for the understanding of the nature of physics (12)(13)(14). Examining their high-pressure behavior and exploring the possible metallization and superconductivity in this system are the focus of this work.We have explored the crystal structures of lithium-rich compounds CLi n in a wide pressure range from ambient pressure to 300 GPa. Fig. 1 shows the enthalpy-pressure curves of CLi 4 and the possible decomposition to the elements and compounds. The other possible lithium-rich carbides CLi n (n = 2 ∼ 6) and their stabilities can be found in SI Appendix, Fig. S1. Obviously, the compound of CLi 4 is stable at least above 3 GPa and below 300 GPa. Before about 3 GPa, CLi 4 is unstable and decomposes into a C 2 Li 2 and Li mixture. After about 3 GPa, CLi 4 com...

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“…The dumbbell units in Li 2 C 2 are expected to polymerize into zigzag chains of carbon atoms at pressures around 5 GPa, 6 and the system develops into semimetals (P -3m1-Li 2 C 2 ) and metals (Cmcm-Li 2 C 2 ) with polymeric anions (chains, layers, strands) by increasing pressure up to 20 GPa, and semimetallic P -3m1-Li 2 C 2 displays an electronic structure close to that of graphene. 4,7 By¯rst-principles total energy calculations, it is shown that in the athermal limit the orthorhombic polymorph of Cs 2 C 2 is more stable by about 7 kJ/mol with respect to the hexagonal modi¯cation, while for Rb 2 C 2 the orthorhombic polymorph is more stable by around 4 kJ/mol. 8 Prior to those theoretical researches, many experiments have been done to address their crystal structure.…”

Section: Introductionmentioning

confidence: 96%

The structural, elastic and electronic properties of A₂C₂ (A = Li, Na, K, Rb and Cs): First-principles calculations

Tang

Sun

2015

Int. J. Mod. Phys. C

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The structural, elastic and electronic properties of A 2 C 2 (A¼Li, Na, K, Rb and Cs) at zero temperature were investigated by¯rst-principles total energy calculations. The optimized equilibrium structural parameters agree well with available experimental values. Elastic constants, bulk modulus, Young's modulus and Poissons ratio were given. All the structures studied are stable mechanically and all stable A 2 C 2 studied has strong compressibility, which originates from weak Coulomb repulsion between metal atoms and carbon atoms. The electronic structure calculations show that binary alkali metal carbides studied here are insulators.

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Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure

Cited by 38 publications

References 37 publications

Reversible reduction of Li₂CO₃

Reversible reduction of Li₂CO₃

Crossover from metal to insulator in dense lithium-rich compound CLi ₄

The structural, elastic and electronic properties of A₂C₂ (A = Li, Na, K, Rb and Cs): First-principles calculations

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Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure

Cited by 38 publications

References 37 publications

Reversible reduction of Li2CO3

Reversible reduction of Li2CO3

Crossover from metal to insulator in dense lithium-rich compound CLi 4

The structural, elastic and electronic properties of A2C2 (A = Li, Na, K, Rb and Cs): First-principles calculations

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Reversible reduction of Li₂CO₃

Reversible reduction of Li₂CO₃

Crossover from metal to insulator in dense lithium-rich compound CLi ₄

The structural, elastic and electronic properties of A₂C₂ (A = Li, Na, K, Rb and Cs): First-principles calculations