Abstract
Carbon-bearing compounds display intriguing structural diversity, due to variations in hybrid bonding of carbon. Here, first-principles calculations and unbiased structure searches on yttrium dicarbide at pressure reveal four new structures with varying carbon polymerisation, in addition to the experimentally observed high-temperature low-pressure I4/mmm dimer phase. At low pressures, a metallic C2/m phase (four-member single-chain carbide) is stable, which transforms into a Pnma phase (single-chain carbide) upon increasing pressure, with further transformation to an Immm structure (double-chain carbide) at 54 GPa and then to a P6/mmm phase (sheet carbide) at 267 GPa. Yttrium dicarbide is structurally diverse, with carbon bonded as dimers (at lowest pressure), four-member single chains, infinite single chains, double chains and eventually sheet structures on compression. Electron–phonon coupling calculations indicate that the high-pressure phases are superconducting. Our results aid the understanding and design of new superconductors and illuminate pressure-induced carbon polymerisation in carbides.
Highlights
Carbon-bearing compounds display intriguing structural diversity, due to variations in hybrid bonding of carbon
In carbon-bearing solids, the ability of carbon to form both sp2 − and sp3− bonding states leads to exceptional structural diversity and chemical variation, especially under non-ambient conditions
Other rare-earth-containing carbides, including Y2C3, La2C3, Y1-xThxC2, Y1-xCaxC2, and LaC2 have been found to be superconductors at ambient pressure[12,13,14]. This family of rare-earth carbides have, recently attracted renewed interest owing to the discovery of superconductivity in the layered yttrium carbide halides Y2C2I2 (Tc = 9.97 K) and Y2C2Br2 (Tc = 5.04 K)[15]
Summary
Carbon-bearing compounds display intriguing structural diversity, due to variations in hybrid bonding of carbon. First-principles calculations and unbiased structure searches on yttrium dicarbide at pressure reveal four new structures with varying carbon polymerisation, in addition to the experimentally observed high-temperature low-pressure I4/mmm dimer phase. In carbon-bearing solids, the ability of carbon to form both sp2 − and sp3− bonding states leads to exceptional structural diversity and chemical variation, especially under non-ambient conditions. Yttrium’s hydrides are even predicted to be room-temperature superconductors, with a predicted Tc in YH6 of 264 K at 120 GPa and for YH10 a Tc of 305–326 K at 250 GPa16–18 This leads to the obvious need to explore potential superconductivity in compounds of yttrium with other light elements. Among the most pressing are: (1) How do C2 dimers evolve upon the application of increased pressure? (2) Do any new high-pressure phases display metallic properties? And (3) do any new metallic high-pressure phases show superconductivity? The approach that we have adopted to investigate the structural properties of YC2 at high pressure exploit developments in global structural searching schemes, combined with first-principles total energy calculations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
