High-pressure synthesis of seven lanthanum hydrides with a significant variability of hydrogen content

Abstract

The lanthanum-hydrogen system has attracted significant attention following the report of superconductivity in LaH10 at near-ambient temperatures and high pressures. Phases other than LaH10 are suspected to be synthesized based on both powder X-ray diffraction and resistivity data, although they have not yet been identified. Here, we present the results of our single-crystal X-ray diffraction studies on this system, supported by density functional theory calculations, which reveal an unexpected chemical and structural diversity of lanthanum hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides were produced, LaH3, LaH~4, LaH4+δ, La4H23, LaH6+δ, LaH9+δ, and LaH10+δ, and the atomic coordinates of lanthanum in their structures determined. The regularities in rare-earth element hydrides unveiled here provide clues to guide the search for other synthesizable hydrides and candidate high-temperature superconductors. The hydrogen content variability in lanthanum hydrides and the samples’ phase heterogeneity underline the challenges related to assessing potentially superconducting phases and the nature of electronic transitions in high-pressure hydrides.

Polymer Research at the State Key Laboratory of Supramolecular Structure and Materials, Jilin University

“…The Im-3m-Ca/YH6 13,14,24,25 and Fm-3m-La/YH10 13,14 adopt the known solidate and zeolite structures. The structures of experimental synthesis Pm-3n-Ba/La/Lu/Eu4H23 [26][27][28][29] and theoretical prediction Fd-3m-Li2La/YH17 30 are equal to the so-called type-I and type-II silicon clathrate structures 31 , respectively. This type-I clathrate structure is the Weaire−Phelan foam structure, the optimal solution to the Kelvin problem so far 32 .…”

Anionic N18 Macrocycles and a Polynitrogen Double Helix in Novel Yttrium Polynitrides YN6 and Y2N11 at 100 GPa

“…The metallicity through the nitrogen πsystem explains the observation of non-standard charges and bond multiplicities in the nitrogen units. Worth noting is also that the anion-driven metallicity was found for the majority of high-pressure di-and poly-nitrides, [2,7,8,25,26,54] which, therefore, seems to be a regular phenomenon for high-pressure nitrides.…”

“…Non-integer charges and bond orders were previously reported in metallic nitrides under high pressure. [2,7,8,26] Although 18-membered cycles are not common, they are known for a number of organic compounds. As an example, one can mention 18-crown-6 ether, whose molecule is nonplanar as all ring-forming atoms are sp 3 -hybridized.…”

“…However, over the past 20 years, it has been shown that at high pressure nitrogen's chemistry significantly changes. For example, charged nitrogen N 2 xÀ dimers, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] tetranitrogen N 4 4À units, [17] pentazolate N 5…”

“…[38] Recently, YN 5 , YN 8, and YN 10 with polynitrogen chains, fused N 18 rings and isolated N 5 rings, respectively, were predicted to be stable near 100 GPa and are all promising prospects as high energy density materials. [37] Whereas a significant number of studies on binary metal-nitrogen compounds of alkali, alkaline earth, and transition metal elements under high pressure have been conducted, [1][2][3][4][5][6][7] the high-pressure chemistry and physical properties of rare earth metal nitrides are almost unknown. Until recently, in the yttrium-nitrogen system, only one binary YÀ N compound was known: cubic yttrium nitride YN with the rock salt structure.…”