AUTHOR=Puphal P. , Pomjakushin V. , Ortiz R. A. , Hammoud S. , Isobe M. , Keimer B. , Hepting M. 

TITLE=Investigation of Hydrogen Incorporations in Bulk Infinite-Layer Nickelates

JOURNAL=Frontiers in Physics

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2022.842578

DOI=10.3389/fphy.2022.842578

ISSN=2296-424X

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.