Superconductive sodalite-like clathrate calcium hydride at high pressures

By Hui Wang, J. Tse, Kaori Tanaka, T. Iitaka, Yanming Ma. Proceedings of the National Academy of Sciences of the United States of America, 2012

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Hydrogen-rich compounds hold promise as high-temperature superconductors under high pressures. Recent theoretical hydride structures on achieving high-pressure superconductivity are composed mainly of H2 fragments. Through a systematic investigation of Ca hydrides with different hydrogen contents using particle-swam optimization structural search, we show that in the stoichiometry CaH6 a body-centered cubic structure with hydrogen that forms unusual “sodalite” cages containing enclathrated Ca stabilizes above pressure 150 GPa. The stability of this structure is derived from the acceptance by two H2 of electrons donated by Ca forming an “H4” unit as the building block in the construction of the three-dimensional sodalite cage. This unique structure has a partial occupation of the degenerated orbitals at the zone center. The resultant dynamic Jahn–Teller effect helps to enhance electron–phonon coupling and leads to superconductivity of CaH6. A superconducting critical temperature (Tc) of 220–235 K at 150 GPa obtained from the solution of the Eliashberg equations is the highest among all hydrides studied thus far.

Subfields: Condensed Matter Physics, Geophysics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/3365f6442806f16a924b8f42316499a4c5908ecb

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Citations in the corpus

Structure and superconductivity of hydrides at high pressures (2017, background): “Recent theoretical work indicated that by compression, three stoichiometries CaH4, CaH6 and CaH12 become energetically stable [15].”
A perspective on conventional high-temperature superconductors at high pressure: Methods and materials (2019, background): “A substantial amount of computational studies have been published and in some of them spectacular values close or above room temperature have been predicted [176, 177].”
Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure (2017, methodology): “The superconductivity calculations were performed with the Quantum-ESPRESSO package (17)·”
On Distribution of Superconductivity in Metal Hydrides (2018, background): “at much lower pressure than its analog Im m 3̄ -CaH6 [17] (200 GPa).”