Issue Date: October 12, 2009
Metallizing Hydrogen, With A Little Lithium
Theoretical work indicates that adding an electropositive atom to hydrogen could make it easier to metallize the element to produce a room-temperature superconductor, reports a group led by Eva Zurek at Cornell University (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0908262106). Efforts to obtain pure hydrogen metal in the lab have largely failed because the necessary pressure—probably around 400 gigapascals—can’t be reached with steady forces. Zurek and colleagues computationally evaluated the enthalpies of various LiHn complexes, all of which appeared to become stable metallic materials around 100–165 GPa. The researchers found that LiH2 and LiH3 form a structure composed of H2 guest molecules in an ionic Li+H– host lattice. The overlap of the H– and H2 wave functions results in metallization. For LiH4, LiH6, and LiH8, all of the hydrogen exists as slightly stretched H2 molecules, with metallization arising from electron transfer from lithium. In the case of LiH6, Li+ and 3(H2)– form. And as for LiH5 and LiH7, they can take shape as either structure type. These results may point to new ways to metallize hydrogen experimentally, the researchers say.
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