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The 27th AIRAPT International Conference on High Pressure Science and Technology
Abstract

Oral


Search for superhydrides and superconductivity in Pd-H, Pb-H and U-H systems.

Authors:
Bastien Guigue (ESPCI - Ecole Supérieure de Physique et de Chimie Industrielles de la ville de Paris, CEA - Commissariat à l'Energie Atomique) ; Adrien Marizy (CEA - Commissariat à l'Energie Atomique) ; Brigitte Leridon (ESPCI - Ecole Supérieure de Physique et de Chimie Industrielles de la ville de Paris) ; Paul Loubeyre (CEA - Commissariat à l'Energie Atomique)

Abstract:

There is a great current interest in the synthesis and characterization of superhydrides, as hydrogen solubility in metals drastically increases under pressure. Polyhydrides with nontraditional stoichiometries have now been predicted stable for most elements of the periodic table at sufficiently high pressure when embedded in excess hydrogen. Interestingly also, these superhydrides should form a novel class of high-TC superconductors. Yet, their experimental observation is less advanced. Only few superhydrides have up to now been synthesized. In particular, the recent results on H3S [1] and LaH10 [2,3] are extremely encouraging with evidence of superconductivity at high temperature, at 200 K and 260 K respectively. It thus seems important to progress in the making of a corpus of experimental data on the synthesis pressure, stoichiometry, structure and superconducting temperature of those superhydrides that should be obtained by direct reaction of hydrogen with elements under pressure.

In this talk, we will present our search for superhydrides in Pd-H, Pb-H and U-H systems. Comparison with calculations will be discussed.

  1. The emergence of superconductivity around 8 K in Pd, due to the solubility of H in Pd up to PdH, was a surprise more than forty years ago and since then has been thoroughly studied. The possibility of achieving higher TC in PdHx is still debated. We have searched for a possible increase of the H concentration in the Pd-based hydride by going up to the 100 GPa pressure range and by using laser heating. Isotope effects have been measured. Nano-structuration effects have also been investigated. A combined structural study together with magnetic measurements with a special amagnetic cell [4] allowed us to get a comprehensive picture of this system.

  2. According to calculations, lead should form the PbH4 hydride above 134 GPa [5], with remarkable dynamical properties because of a total decoupling of the phonon spectra of lead and hydrogen. We have investigated the formation of lead hydrides by compressing Pb in excess hydrogen up to 150 GPa, and by using laser heating. No hydride could be synthesized. We have also investigated the effect of Li impurities that could lower the hydride formation pressure. Direct reaction of H with the Pb83Li17 alloy, key component of the ITER wall, has been investigated.

  3. Eventually, we have conducted a study of the U-H system up to 100 GPa, synthesizing two new hydrides (UH7 and UH8). UH7 is particularly interesting since it should be superconducting with a TC around 70 K [6]. We found it stable above 37 GPa. Superconductivity measurements are in progress using a mini-DAC designed for SQUID measurements.

 

 

[1] A. P. Drozdov et al., Nature 525, 73–76 (2015)

[2] M. Somayazulu et al., Phys. Rev. Lett. 122, 027001 (2019)

[3] A. P. Drozdov et al., arXiv:1812.01561 (2018)

[4] A. Marizy et al., High Pressure Research 37, 465-474 (2017)

[5] Y. Cheng et al., Sci Rep. 5, 16475 (2015)

[6] I. A. Kruglov, Science Advances 4, 10 (2018)