Team Finds Unexpected Hydrides Become Stable Metals at Pressure Near One Quarter Required to Metalize Pure Hydrogen Alone

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Team Finds Unexpected Hydrides Become Stable Metals at Pressure Near One Quarter Required to Metalize Pure Hydrogen Alone

STONY BROOK, October 12, 2009 – From detailed assessments of electronic structure, researchers at the University at Buffalo, Cornell University, Stony Brook University and Moscow State University discovered that unexpected hydrides violating standard valence rules, such as LiH6 and LiH8, become stable metals at a pressure approximately one quarter of that required to metalize pure hydrogen itself; findings that were published in an October 5, 2009 early edition of the Proceedings of the National Academy of Sciences. The paper, entitled "A little bit of lithium does a lot for hydrogen," presents the first prediction of stable LiHn hydrides (LiH2, LiH6, LiH8). These hypothetical materials demonstrate that nontraditional stoichiometries can considerably expand the view of chemical bonding already under moderate pressure.





 
Figure: Predicted stable structures of metallic LiH2 (left) and LiH6 (right). Green – lithium atoms, white and pink – hydrogen atoms.
Metallic hydrogen, believed to be stable at high pressures, is theorized to be a superconductor at record high temperatures of at least a few hundred Kelvin (room temperature or higher). Due to its high (100%) hydrogen content and high density it is the ultimate energy storage material – if it can be synthesized in large quantities and subsequently brought to ambient conditions in the same metallic form.





For decades, researchers at the top research institutions around the world have predicted exotic properties for metallic hydrogen, but no credible reports of experimental synthesis of solid metallic hydrogen ever appeared because of two primary obstacles. First, metallization of hydrogen requires pressures of about four million atmospheres, which was out of reach of static compression techniques. Extreme pressures, even if they could be reached, imply that only tiny amounts of the material can be prepared, which would be of little practical use. Second, the recovery of this high pressure material to ambient pressure ...

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