Synthesis of lithium polyhydrides above 130 GPa at 300 K

Abstract

The prediction of novel lithium hydrides with nontraditional stoichiometries at high pressure has been seminal for highlighting a promising line of research on hydrogen-dense materials. Here, we report the evidences of the disproportionation of LiH above 130 GPa to form lithium hydrides containing H 2 units. Measurements have been performed using the nonperturbing technique of synchrotron infrared absorption. The observed vibron frequencies match the predictions for LiH 2 and LiH 6 . These polyhydrides remain insulating up to 215 GPa. A disproportionation mechanism based on the diffusion of lithium into the diamond anvil and a stratification of the sample into LiH 6 /LiH 2 /LiH layers is proposed. Polyhydrides containing an H 2 sublattice do exist and could be ubiquitously stable at high pressure.high pressure | hydride chemistry | hydrogen stoichiometry

Lithium polyhydrides synthesized under high pressure and high temperature

“…The observed Raman shifts are plotted as a function of pressure in Fig. (a) together with the previously reported results for Raman active modes of LiH, the Raman vibrons [ Q 1( J ) Raman ] of pure H 2 , the IR absorbance measurement of LiH n , and the most intense calculated phonon of LiH 2 . It can be found that the pressure dependence of the Raman shift of ‘bulk H 2 ’ indicated by the closed square in Fig.…”

“…Pressure dependences of Raman shifts for the ν1–ν9 (a) and the full width at the half height of ‘bulk H 2 ’ and Q 1( J ) Raman of pure H 2 (b). In (a), the Raman vibrons [ Q 1( J ) Raman ] of pure H 2 , Raman active modes of LiH, the calculated phonon of LiH 2 , the IR absorption peak wavenumber for LiH n , and the calculated vibron of the elongated H 2 in CsH 7 , BaH 6 , and RbH 5 are plotted together . [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Very recently, Pépin et al . have reported that LiH 2 and LiH 6 are possibly synthesized when LiH chemically reacts with diamond anvils under pressures exceeding 130 GPa . In this study, in order to investigate further the structural properties of the LiH n that was synthesized by the laser heating under high pressure and search for its metallic state, we performed the extensive measurements of Raman scattering up to 182 GPa at room temperature.…”

Hydrogen sulfide at high pressure: Change in stoichiometry

“…Novel polyhydrides predicted theoretically to become stable at high pressure [2,3] are good candidates to realize such expectations but several experimental efforts were inconclusive [4][5][6]. Recently, however, following the theoretical prediction [3], superconductivity up to 203 K in the H-S system at above 144 GPa has been reported [7,8].…”

Superconductivity in Hydrides Doped with Main Group Elements Under Pressure

“…Since then, numerous theoretical studies have been performed that investigate the phase diagrams of hydrogen doped with the electropositive alkali metals or alkaline earth metals [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], as well as the electronegative element iodine [35,36] under pressure. Experimental work on the hydrides of lithium and sodium confirmed that species with unique stoichiometries such as NaH 3 and NaH 7 can be synthesized in diamond anvil cells, but the phases that have been reported to date do not exhibit superconductivity [21,37]. Nonetheless, as summarized in this short review, the aforementioned theoretical explorations have: revealed that rich structural variety may be found in the hydrogenic sublattices, suggested a number of ways that hydrogen may be metalized via doping, and shown that the propensity for superconductivity is linked to the nature of the hydrogenic motifs.…”