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arXiv · 2204.03023

Investigation of hydrogen incorporations in bulk infinite-layer nickelates

Pascal Puphal·Vladimir Pomjakushin·Roberto A. Ortiz·Samir Hammoud·Masahiko Isobe·Bernhard Keimer·Matthias Hepting
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Abstract

Infinite-layer (IL) nickelates are an emerging class of superconductors, where the Ni$^{1+}$ valence state in a square planar NiO$_2$ coordination can only be reached via topotactic reduction of the perovskite phase. However, this topotactic soft chemistry with hydrogenous reagents is still at a stage of rapid development, and there is a number of open issues, especially considering the possibility of hydrogen incorporation. Here we study the time dependence of the topotactic transformation of LaNiO$_3$ to LaNiO$_2$ for powder samples with x-ray diffraction and gas extraction techniques. While the hydrogen content of the powder increases with time, neutron diffraction shows no negative scattering of hydrogen in the LaNiO$_2$ crystal lattice. The extra hydrogen appears to be confined to grain boundaries or secondary-phase precipitates. The average crystal structure, and possibly also the physical properties, of the primary LaNiO$_2$ phase are therefore not noticeably affected by hydrogen residues created by the topotactic transformation.

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Pascal Puphal, Vladimir Pomjakushin, Roberto A. Ortiz, Samir Hammoud, Masahiko Isobe, Bernhard Keimer, Matthias Hepting. 2022-04-06. Investigation of hydrogen incorporations in bulk infinite-layer nickelates. https://doi.org/10.3389/fphy.2022.842578

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