| To metalize pure hydrogen is scientists’ dream all the time sincemetallic hydrogen is expected to show exotic properties such assuperfluidity and high-temperature superconductivity. But so far Staticcompression experiments have shown that hydrogen is an insulator atroom temperature up to pressures of at least342GPa. Theoretically solidhydrogen can become metallic due to either pressure-induced bandoverlap of molecular hydrogen or molecular dissociation（molecular-to-monatomic transition）.Since Ashcroft predicted that certain hydrides would present a highsuperconducting critical temperature while becoming metallic at lowerpressures than pure solid hydrogen, dense hydrides have becomeresearchers’ target of research to study metallization and findhigh-temperature superconductors, such as AlH3, Si2H6, SiH4, GeH4andSnH4. Recently, Van der Waals H2-containing compounds have attractedmany people’s interest of research, because experiments have unexpectedly revealed that H2molecules can interact with hydrides CH4,SiH4, H2O, and NH3BH3, and even with inert gas Ar and Xe at readilyaccessible pressures with the formation of intriguing van der Waalscompounds CH4-H2, SiH4-H2, H2O-H2, NH3BH3-H2, Ar-H2, and Xe-H2.These H2-containing compounds are of interest as models for studyingmetallic hydrogen and hydrides. How H2molecules change in hydridesand what contribution H2molecules do to metallization are attractive.As a material proposed for storing hydrogen and promised adding torocket fuels and high explosives, aluminum hydride have received widelystudy. In view of the low metallization pressure observed in AlH3, wehave then targeted on the metallization and superconductivity of AlH3-H2by first-principles calculations via genetic algorithm on crystal structureprediction and linear response theory on electron-phonon coupling （EPC）calculations.The high-pressure structures of AlH3（H2） in the pressure range25–300GPa were extensively explored by using a genetic algorithm. Wehave found an insulating P1phase and a semiconducting P-1phase withpressure below250GPa, above which a intriguing sandwichlike metallicphase with structure of P21/mZ （containing Z shape net layers of Alatoms） replaced. It is hard to got metallic hydrogen. But we found the H2molecules in the environment of AlH3become metallic and showmolecular semimolecular. Application of the Allen-Dynes modified McMillan equation yields remarkably high superconducting temperaturesof132–146K at250GPa, among the highest values reported so far forphonon-mediated superconductors. Analysis reveals a uniquesuperconducting mechanism that the direct interactions between H2andAlH3at high pressure play the major role in the high superconductivity. |
