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 EuH9, hexagonal EuH9, and an unexpected cubic (Pm3n) clathrate phase, Eu8H46. Monte Carlo simulations indicate that cubic EuH9 has antiferromagnetic ordering with TN of up to 24 K, whereas hexagonal EuH9 and Pm3n-Eu8H46 possess ferromagnetic ordering with TC = 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 EuH9. 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.
Author ORCID Identifier
Alexander I. Boldyrev https://orcid.org/0000-0002-8277-3669
Nikolay Tkachenko https://orcid.org/0000-0002-7296-4293
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NSF, Division of Chemistry (CHE)
NSF, Division of Chemistry (CHE) 1664379
Deciphering Delocalized Bonding in Excited States, Solvated Species and Novel 0-, 1-, 2-, and 3-Dimensional Chemical Systems
To investigate the formation of new chemical compounds in the Eu–H system, we purchased the europium foil with 99.99% purity from Alfa Aesar company. Two diamond anvil cells (DACs) with 100 and 150 μm culets were loaded with Eu and ammonia borane (AB), purified by sublimation, which was used as a source of hydrogen and a pressure transmitting medium (Table S1). As has been shown earlier in the synthesis of superhydrides of lanthanum,1 thorium,2 praseodymium,3 and neodymium,4 ammonia borane is an effective source of hydrogen when the metal target is heated by a short (< 0.2 s) laser pulse due to the well-known thermal decomposition reaction: NH3BH3 →H2 + poly-(BNHx)n.5,6 A tungsten plate with a thickness of 20 ± 2 μm was used as a gasket. The pressure was determined by the Raman signal of diamond.7 Heating was carried out by pulses of an infrared laser (1 μm, Nd:YAG). A part of the X-ray diffraction (XRD) patterns of all samples studied in diamond anvil cells were recorded on 4W2 beamline of the Beijing Synchrotron Research Facilities (BSRF, China) and BL15U1 synchrotron beamline at the Shanghai Synchrotron Research Facility (SSRF, China)8 using a focused (5×12 μm) monochromatic X-ray beam (20 keV, 0.6199 Å). The other part of the high-pressure XRD patterns were obtained at BL10XU in SPring-8 using monochromatic synchrotron radiation and an imaging plate detector at room temperature.9 The X-ray beam with a wavelength of 0.413 Å was focused with a polymer compound refractive lens (SU-8, produced by ANKA). The experimental X-ray diffraction images were analyzed and integrated using Dioptas software package.10 The full profile analysis of the diffraction patterns and calculations of the unit cell parameters were performed in JANA200611 using the Le Bail method.12 Additional parameters of high-pressure diamond anvil cells are listed in Table S1.
Semenok, D. V., Zhou, D., Kvashnin, A. G., Huang, X., Galasso, M., Kruglov, I. A., Ivanova, A. G., Gavriliuk, A. G., Chen, W., Tkachenko, N. V., Boldyrev, A. I., Troyan, I., Oganov, A. R., & Cui, T. (2021). Novel Strongly Correlated Europium Superhydrides. The Journal of Physical Chemistry Letters, 12(1), 32–40. https://doi.org/10.1021/acs.jpclett.0c03331
This work is licensed under a Creative Commons Attribution 4.0 License.
Boldyrev, A. I., & Tkachenko, N. (2021). Data from: Novel Strongly Correlated Europium Superhydrides. Utah State University. https://doi.org/10.26078/PKGD-4V24
Additional FilesREADME.txt (4 kB)
Cluster_ELF_plots.zip (2844 kB)
Solid_state_chamical_bonding.zip (10 kB)
Solid_state_ELF.zip (264 kB)
Supplementary_Information.pdf (5664 kB)