Rare Earth Hydrides Research Articles

Low-pressure superconductivity of Th-B-H ternary compounds: An insightful study of stable and metastable phases

The low-enthalpy structures of Th-B-H ternary compounds below 50 GPa are investigated by using an efficient framework that combines high-throughput screening, genetic algorithms, and first-principles calculations. Four thermodynamically stable hydrides (Th2BH11, Th2BH10, ThB2H10, and ThBH) and seven thermodynamically metastable hydrides (ThBH2, ThBH3, ThBH4, ThBH5, ThBH7, ThB2H4, and ThB3H3) are revealed. There are no stable thorium boron hydrides at ambient pressure. R3m-ThB2H10 and R3m-Th2BH11 are indirect bandgap semiconductors, while R3m-Th2BH10 and P6/mmm-ThBH show metallic nature. The relatively low λ values of R3m-Th2BH10 and P6/mmm-ThBH result in their Tc around 5.8 K and 0.1 K at 20 GPa, respectively. Two metastable phases, F4¯3m-ThBH5 and P63/mmc-ThBH7, exhibit excellent superconducting properties at low pressures. The values of Tc of F4¯3m-ThBH5 and P63/mmc-ThBH7 reach 46.9 K at 20 GPa and 40.0 K at 50 GPa, respectively. Our findings offer valuable insights for discovering and designing superconducting rare earth hydrides under low and even ambient pressures.

Effect of Carbon-Supported Rare Earth Oxide Catalysts on the Microstructure, Hydrogen Storage Kinetics, and Thermodynamics of Mg-La-Ni Alloys

In this study, using an improved chemical vapor deposition carbonization method, Eu2O3@C, PrO1.83@C, and La2O3@C composite catalysts were successfully synthesized and incorporated into Mg96La3Ni alloys via ball milling. These catalysts significantly enhanced the hydrogen storage properties of the alloys, particularly in terms of hydrogenation kinetics. Among the catalysts, PrO1.83@C demonstrated the most significant improvement. At 360 °C, the Mg96La3Ni alloy containing 3 wt.% PrO1.83@C achieved a 75.1% hydrogenation saturation ratio within 2 minutes and released 3 wt.% H2 in 3.1 minutes. While the catalysts did not significantly alter the alloy's thermodynamics, they substantially reduced the dehydrogenation activation energy. The addition of 3 wt.% Eu2O3@C, PrO1.83@C, and La2O3@C lowered the activation energy barriers to 116.6, 101.4, and 114.8 kJ/mol H2, respectively, compared to 121.67 kJ/mol H2 for the pristine Mg96La3Ni alloy. This enhancement is attributed to the synergistic effects of the "hydrogen pump" mechanism of rare earth hydrides and the abundant active sites provided by the carbon component, which collectively promote faster hydrogen diffusion and nucleation reactions.

Reduction of Carboxamides Into Amines Catalyzed by La[NH‐2,6‐iPr2‐4‐FcC6H2]3/HBpin

ABSTRACTReduction of carboxamides is an efficient approach to obtain the corresponding amines, albeit it is one of the most problematic. In this work, by use of pinacolborane (HBpin) as a reductant, the rare‐earth metal tris (arylamido) complex supported by a ferrocenyl‐modified arylamido ligand La[NH‐2,6‐iPr2‐4‐FcC6H2]3 was employed as a precatalyst for primary and secondary amide reductions. This catalyst system exhibited high activity toward hydroborative reduction of amides to amines under mild conditions, as well good tolerance for heteroatoms and functional groups in the reduction. A lanthanide hydride was experimentally verified as the active species and the reduction mechanism was proposed.

Superconducting properties of rare-earth boron hydrides at high pressure studied by first-principles calculations

Superconducting properties of rare-earth boron hydrides at high pressure studied by first-principles calculations

Emerging superconductivity rules in rare-earth and alkaline-earth metal hydrides

Hydrides of alkaline-earth and rare-earth metals have garnered significant interest in high-temperature superconductor research due to their excellent electron-phonon coupling and high T c upon pressurization. This study explores the electronic structures and electron-phonon coupling of metal hydrides XHn (n= 4,6), where X includes Ca, Mg, Sc, and Y. The involvement of d-orbital electrons alters the Fermi surface, leading to saddle-point nesting and a charge density wave (CDW) phase transition, which opens the superconducting gap. For instance, in YH6, the exchange coupling between Y-4d and H-1s holes in the phonon softening region results in T c values up to 230 K. The study suggests that factors, such as the origin of the CDW order, hydrogen concentration, and d-orbital contributions are crucial to superconductivity. This work proposes a new rule for high T c superconductors, emphasizing the importance of double gaps and electron-phonon interactions at exchange coupling sites, and predicts potential high-quality superconductors among rare-earth hydrides.

From high-temperature superconductivity to room-temperature superconductivity: From ambient to high pressure; from very high pressure to ambient again!?

This article will first briefly review the impressive advancements made in high-temperature superconductivity (HTS) before the arrival of room-temperature superconductivity (RTS). Accompanying the advancements made in superconductivity science and technology over the last century, a solid experimental framework concerning the search, development, and even authentication of new discoveries has been established. All these can serve as valuable references in the infancy of RTS research. In this spirit, we will comment on the current status of rare-earth hydride RTS and present our preliminary negative results on Lu-N-H and LK-99, the two most studied materials in the search for RTS in the last few months, although several more reports of negation than affirmation have appeared.

Synthesis and Reactivity of Discrete Europium(II) Hydride Complexes.

The bulky β-diketiminate ligand frameworks [BDIDCHP]- and [BDIDipp/Ar]- (BDI=[HC{C(Me)2N-Dipp/Ar}2]- (Dipp=2,6-diisopropylphenyl (Dipp); Ar=2,6-dicyclohexylphyenyl (DCHP) or 2,4,6-tricyclohexylphyenyl (TCHP)) have been developed for the kinetic stabilisation of the first europium (II) hydride complexes, [(BDIDCHP)Eu(μ-H)]2, [(BDIDipp/DCHP)Eu(μ-H)]2 and [(BDIDipp/TCHP)Eu(μ-H)]2, respectively. These complexes represent the first step beyond the current lanthanide(II) hydrides that are all based on ytterbium. Tuning the steric profile of β-diketiminate ligands from a symmetrical to unsymmetrical disposition, enhanced solubility and stability in the solution-state. This provides the first opportunity to study the structure and bonding of these novel Eu(II) hydride complexes crystallographically, spectroscopically and computationally, with their preliminary reactivity investigated.

Synthesis of cubic lutetium hydride at HPHT conditions and its implications

Binary rare earth hydrides are ideal hydrogen rich materials for the search of room temperature superconductivity. Even though there are plethora of such theoretical predictions, only a few binary hydrides show high TC experimentally. The recent progress in the search for new ternary hydrides have led to the controversial discovery of room temperature superconductivity in the nitrogen doped lutetium hydride (LuH3-δNε) (NLH). This has stimulated the interest in the synthesis of lutetium hydrides and their detailed understanding. Phase pure LuH2 has been synthesized using pure Lutetium (Lu) metal and paraffin as hydrogen source at high pressure and high temperature conditions. The sample inside diamond anvil cell (DAC) has been characterised with optical micrographs using high resolution optical microscope. The recovered sample is characterised by employing synchrotron based angle dispersive x-ray diffraction (ADXRD) measurements. The lattice parameter of as synthesized LuH2 is in excellent agreement with the earlier reported one. The comparison of high pressure evolution of the unit cell volumes of synthesized LuH2, cubic LuH3 and NLH imparts broader understanding and opens the way for future research in lutetium based hydride systems. Data analysis at high pressures reveals that the parent structural framework of NLH is LuH2 rather than LuH3. Here, we have proposed a novel method for determination of hydrogen stoichiometry in ternary rare earth hydride systems. In this method, hydrogen to metal ratio (H:M) and metal-hydrogen (M − H) distance as a function of hydrogen-solubilities systematics for lanthanide dihydrides solid solution are utilized to constrain the concentration of hydrogen in these compounds.

Multi-electron redox reactivity of a samarium(ii) hydrido complex.

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb2+ and Eu2+ centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(CpAr5)SmII(μ-H)(DABCO)]2 (4) (CpAr5 = C5Ar5, Ar = 3,5-iPr2-C6H3; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(CpAr5)SmII{CH(SiMe3)2}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates. Exposure of complex 4 to CO2 results in the formation of the trivalent samarium(iii) mixed-bis-formate/carbonate complex [(CpAr5)SmIII(μ-η2:η1-O2CH)(μ-η2:η2-CO3)(μ-η1:η1-O2CH)SmIII(CpAr5)(DABCO)] (8), mediated by hydride insertion and reductive disproportionation reactions. Complex 4 shows four-electron reduction toward four equivalents of CS2 to afford the trivalent samarium(iii) bis-trithiocarbonate complex [(CpAr5)SmIII(μ-η2:η2-CS3)(DABCO)]2 (9). A mechanistic study of the formation of complex 8 was carried out using DFT calculations.

Tuning rare-earth hydride reactivity with a reductive diazabutadienyl ligand beyond insertion

An unusual hydrogen radical addition and SET process between one H- and two DAD’ ligands has been observed in the reaction of 2 with PhCCH.

The investigation on exploring rare earth hydrides superconductors

This review provides a comprehensive overview of the challenges and potential solutions in the quest for high-temperature superconductivity using hydrogen-rich materials. Traditional superconductors often face limitations in terms of critical transition temperatures (Tc) and stability under high pressures. However, hydrogen-rich compounds offer promising avenues due to their strong electron-phonon coupling, elevated Debye temperatures, and high electronic density. Recent discoveries, such as H3S, have further invigorated the field. While an excess of H2-like units can adversely affect Tc, clathrate structures like CaH6 and YH6 present viable alternatives by fostering high symmetry. Rare earth hydrides, notable for their electron-donating capabilities, have undergone extensive testing. Isotope effect studies, as exemplified by LaH10 and LaD10, highlight the critical role of hydrogen vibrations in superconductivity. Ternary superhydrides incorporating dopant elements aim to reduce the pressure requirements for stability, with LaBeH8 emerging as a promising candidate, exhibiting a Tc of 110 K at 80 GPa. The review concludes by outlining future research directions, such as the incorporation of small-radius atoms to increase hydrogen content, a deeper understanding of the role of symmetry, and addressing challenges related to vibrational modes and structural stability.

Enhancement effect of Ce hydride on hydrogen storage performance of Mg(NH2)2-2LiH

Because Mg(NH2)2-2LiH system has a high hydrogen storage capacity and a mild hydrogen release temperature around 125 °C, it can be used as a new generation of on-board hydrogen storage material, but the hydrogen absorption and release kinetics still have great obstacles. In this paper, CeH2.51, a rare earth hydride, was used as a modified catalyst to improve its hydrogen storage performance for the first time. The experimental results showed that the addition of CeH2.51 can significantly improve the hydrogen absorption/desorption kinetics and cycle performance compared with that of the pristine sample Mg(NH2)2-2LiH. And the sample doped with 7.5 wt% CeH2.51 shows the best comprehensive performance. The initial hydrogen release and absorption temperatures drops to 110 °C and 60 °C, respectively, and the activation energy of hydrogen release decreased from 120.0 kJ/mol to 102.5 kJ/mol, the hydrogen storage capacity of has almost no decay after 10 absorption/desorption cycles. In addition, the mechanism of CeH2.51 improving the hydrogen storage performance of Mg(NH2)2-2LiH was also clarified by various characterizations.

Structural Transformation in LnHS (Ln = La, Nd, Gd, and Er) with Coordination Change between an S-Centered Octahedron and a Trigonal Prism

Lanthanide hydride chalcogenides LnHSe and LnHTe (Ln = lanthanides) crystallize in two polymorphs, 2H and 1H structures (ZrBeSi-type and filled-WC-type structures, respectively), but the chemical origin of the structural selection is unknown. Here, we have expanded the LnHCh (Ch = O, Se, and Te) family to include LnHS (Ln = La, Nd, Gd, and Er) using high-pressure synthesis. LnHS adopts the 2H structure for large Ln (La, Nd, and Gd) and the 1H structure for small Er. We compared the two polymorphs using anion-centered polyhedra and found that in the compounds with large ionicity, the 2H structure with ChLn6 octahedra is stabilized over the 1H structure with ChLn6 trigonal prisms due to relatively small electrostatic repulsion, supported by analysis of Madelung energy, crystal orbital Hamilton population (COHP), and density of energy (DOE).

In-situ, real-time investigation of the formation of oxygen-containing rare-earth hydrides by combining a quartz crystal microbalance and ion beam analysis

We present an in-situ and real-time investigation of the formation of YHO and GdHO thin films grown by reactive e−-beam evaporation. Mass changes were continuously monitored during deposition, oxidation, and illumination using a highly sensitive quartz crystal microbalance, while changes in chemical composition and depth profiles were investigated simultaneously by ion beam analysis. Results highlight the strong reactivity of freshly deposited YHx and GdHx films, even under ultra-high vacuum conditions. Oxidation starts at the surfaces of the films and the oxidation rate is strongly dependent on the O2 pressure. The response of the system under ion beam irradiation and in-situ illumination is also presented and discussed. For the measured mass changes, a quantitative agreement better than 2% was observed between both techniques and demonstrates the consistency and sensitivity of this approach.

Predicted High-Temperature Superconductivity in Rare Earth Hydride ErH2 at Moderate Pressure

Hydrides offer an opportunity to study high critical temperature (high-T c) superconductivity at experimentally achievable pressures. However, the pressure needed remains extremely high. Using density functional theory calculations, herein we demonstrate that a new rare earth hydride ErH2 could be superconducting with T c ∼ 80 K at 14.5 GPa, the lowest reported value for compressed hydrides to date. Intriguingly, due to Kondo destruction, superconductivity was prone to exist at 15 GPa. We also reveal an energy gap at 20 GPa on the background of normal metallic states. At 20 GPa, this compressed system could act as a host of superconductor judged from a sharp jump of spontaneous magnetic susceptibility with an evanescent spin density of state at Fermi level. Finally, electron pairing glue for ErH2 at these three typical pressures was attributed to the antiferromagnetic spin fluctuation.

Remarkable kinetics of novel Ni@CeO2–MgH2 hydrogen storage composite

Magnesium hydroxide (MgH2) has excellent reversibility and high capacity, and is one of the most promising materials for hydrogen storage in practical applications. However, it suffers from high dehydrogenation temperature and slow sorption kinetics. Rare earth hydrides and transition metals can both significantly improve the de/hydrogenation kinetics of MgH2. In this work, MgH2–Mg2NiH4–CeH2.73 is in-situ synthesized by introducing Ni@CeO2 into MgH2. The unique coating structure of Ni@CeO2 facilitates homogeneous distribution of synergetic CeH2.73 and Mg2NiH4 catalytic sites in subsequent ball milling process. The as-fabricated composite MgH2-10 wt% Ni@CeO2 powders possess superior hydrogenation/dehydrogenation characteristics, absorbing 4.1 wt% hydrogen within 60 min at 100 °C and releasing 5.44 wt% H2 within 10 min at 350 °C. The apparent activation energy of MgH2-10 wt% Ni@CeO2 is determined to be 84.8 kJ/mol and it has favorable hydrogen cycling stability with almost no decay in capacity after 10 cycles.

The effect of T4 and T6 heat treatments for dynamic impact behavior of casting Mg-Gd-based alloys

The study of dynamic impact properties of Mg–Gd alloy is important for its application in aerospace, automotive manufacturing and weaponry fields. In this work, the dynamic behaviors of the casting solid-solution (T4) and peak-aged (T6) Mg-6.5Gd-3Y-0.5Zr alloys were investigated at different strain rates by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD), transmission electron microscopy(TEM), Vickers hardness testing, and split Hopkinson press bar(SHPB). Due to the dynamic precipitation phase during the SHPB and the residual rare earth hydride(REH) particles produce in the T4 treatment, the compressive strength of the casting T4-sample can reach 485 MPa at a strain rate of 3500 s−1. The casting T6-alloy precipitated a reinforced phase β′ and therefore exhibited an ultra-high compressive strength of 519 MPa at a high strain rate of 4500 s−1. The dynamic compressive strength of a T4 sample is unaffected by strain rates, whereas the dynamic compressive strength of a T6-sample is sensitive. Based on fracture morphology, the cracks are made up of a 45° loading direction crack on the cylindrical surface and a compressed surface crack. The fracture surface is characterized by cleavage planes and dimples. As the deformation strain-rate increases, the number of cleavage planes increases, while the proportion of dimples decreases. Under varied strain rates, it can likewise be deduced that cleavage fracture is the main fracture mechanism of the T6-alloy.

Electron–phonon coupling and superconductivity in an alkaline earth hydride CaH6 at high pressures

Recently, an alkaline earth hydride CaH6 having a sodalitelike clathrate structure has been experimentally synthesized at megabar pressures with a maximum T c of 215 K, comparable to that of a rare earth hydride LaH10. Here, based on first-principles calculations, we find that CaH6 exhibits a huge peak in the Eliashberg spectral function α 2 F around the low-frequency region of H-derived phonon modes, in contrast to LaH10 having a widely spreading spectrum of α 2 F over the whole frequencies of H-derived phonon modes. It is revealed that the huge peak of α 2 F in CaH6 is associated with an effective electron–phonon coupling (EPC) between low-frequency optical phonons and hybridized H 1s and Ca 3d states near the Fermi energy. As pressure increases, the strengthened H–H covalent bonding not only induces a hardening of optical phonon modes but also reduces the electron–phonon matrix elements related to the low-frequency optical modes, thereby leading to a lowering of the EPC constant. It is thus demonstrated that H-derived low-frequency phonon modes play an important role in the pressure-induced variation of T c in CaH6. Furthermore, unlike the presence of two distinct superconducting gaps in LaH10, CaH6 is found to exhibit a single isotropic superconducting gap.

Effect of Gd content on microstructure and dynamic mechanical properties of solution-treated Mg−xGd−3Y−0.5Zr alloy

The effect of Gd content ranging from 6.5 wt.% to 8.5 wt.% on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy and split Hopkinson pressure bar. The microstructure of as-cast Mg−xGd−3Y−0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting. Due to the rapid cooling rate during solidification, a large amount of non-equilibrium eutectic phase Mg24(Gd,Y)5 appears at the grain boundary of as-cast Mg−xGd−3Y−0.5Zr alloys. After solution treatment at 520 °C for 6 h, the Mg24(Gd,Y)5 phase dissolves into the matrix, and the rare earth hydrides (REH) phase appears. The stress−strain curves validate that the solution-treated Mg−xGd−3Y−0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates. It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg−xGd−3Y−0.5Zr alloys.

Superconductivity above 200 K discovered in superhydrides of calcium

Searching for superconductivity with Tc near room temperature is of great interest both for fundamental science & many potential applications. Here we report the experimental discovery of superconductivity with maximum critical temperature (Tc) above 210 K in calcium superhydrides, the new alkali earth hydrides experimentally showing superconductivity above 200 K in addition to sulfur hydride & rare-earth hydride system. The materials are synthesized at the synergetic conditions of 160~190 GPa and ~2000 K using diamond anvil cell combined with in-situ laser heating technique. The superconductivity was studied through in-situ high pressure electric conductance measurements in an applied magnetic field for the sample quenched from high temperature while maintained at high pressures. The upper critical field Hc(0) was estimated to be ~268 T while the GL coherent length is ~11 Å. The in-situ synchrotron X-ray diffraction measurements suggest that the synthesized calcium hydrides are primarily composed of CaH6 while there may also exist other calcium hydrides with different hydrogen contents.