Novel Strongly Correlated Europium Superhydrides

Abstract

We conducted a joint experimental−theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86−130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic EuH 9 , hexagonal EuH 9 , and an unexpected cubic (Pm3n) clathrate phase, Eu 8 H 46 . Monte Carlo simulations indicate that cubic EuH 9 has antiferromagnetic ordering with T N of up to 24 K, whereas hexagonal EuH 9 and Pm3n-Eu 8 H 46 possess ferromagnetic ordering with T C = 137 and 336 K, respectively. The electron−phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes s-wave superconductivity, except, perhaps, for distorted pseudohexagonal EuH 9 . The equations of state predicted within the DFT+U approach (U − J were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.

Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides

“…We look forward to the synthesis and characterization of the I4=mmm symmetry tetrahydrides that have not yet been experimentally realized, and the measurement of superconductivity in those predicted to have non-negligible T c values. We also look forward to future theoretical studies of the effects of strong correlation, spin orbit coupling and magnetism [41][42][43] on the electronic structure of these compounds. Such findings will increase the rich chemistry associated with the ThCr 2 Si 2 prototype structure.…”

“…. Theoretical studies based upon a priori crystal structure prediction have found that MgH 4 , [30] CaH 4 , [31][32][33] SrH 4 , [34,35] ScH 4 , [18,[36][37][38] YH 4 , [18] ZrH 4 , [30] LaH 4 , [19] CeH 4 , [18,39,40] PrH 4 , [18] NdH 4 , [41] EuH 4 , [42] TbH 4 , [43] ThH 4 , [44] PuH 4 , [45] and all of the REH 4 [29] phases assuming this structure type are thermodynamically stable in their respective pressure ranges. Therefore, this I4=mmm structure may be a universal feature in the phase diagram of most of the compressed alkaline and rare earth, as well as a few transition metal and actinide tetrahydrides under pressure.…”

Tuning Chemical Precompression: Theoretical Design and Crystal Chemistry of Novel Hydrides in the Quest for Warm and Light Superconductivity at Ambient Pressures

“…On the other hand, complex electronic structures may necessitate the use of meta-GGA functionals such as SCAN 70 or treatment of dispersion [71][72][73] . However, functionals that go beyond GGA are typically employed only to get a more accurate energy ordering after the CSP search is complete [74][75][76][77] , to manage computational expense. Since GGA-type functionals tend to underestimate metallization that results from pressure induced band broadening, hybrid functionals such as HSE06 78 are often employed to verify metallicity.…”

“…The predicted structure with the highest symmetry is a P 6 3 /mmc arrangement of M@H 29 cages with a [4 6 5 6 6 6 ] framework (Figure 3c), and H-H distances slightly elongated relative to molecular H 2 . Several phases have been predicted to assume this structure, including YH 75 .…”

“…Several polymorphs of ScH 6 have been predicted, with symmetries including Cmcm 107 and P 6 3 /mmc 43,106,107 , suggesting complex phase behavior under pressure. Finally, recent explorations of the rare earth hydrides have identified Pu 76 , Tb 77 , Eu 75 , and Pm-Lu 124 analogues, with TbH 6 having an estimated T c up to 147 K at 300 GPa.…”