Structural instabilities of infinite-layer nickelates from first-principles simulations

Rare-earth nickelates RNiO2 adopting an infinite-layer phase show superconductivity once La, Pr, or Nd is substituted by a divalent cation. Either in the pristine or doped form, these materials are reported to adopt a high symmetry, perfectly symmetric, P-4/mmm tetragonal cell. Nevertheless, bulk compounds are scarce, hindering a full understanding of the role of chemical pressure or strain on lattice distortions that in turn could alter magnetic and electronic properties of the two-dimensional nickelates. Here, by performing a full analysis of the prototypical YNiO2 compound with first-principles simulations, we identify that these materials are prone to exhibit O-4 group rotations whose type and amplitude are governed by the usual R-to-Ni cation size mismatch. We further show that these rotations can be easily tuned by external stimuli modifying lattice parameters such as pressure or strain. Finally, we reveal that H intercalation is favored for any infinite-layer nickelate member and pushes the propensity of the compounds to exhibit octahedra rotations.

Automated summary

This study reveals that rare-earth nickelates are prone to group rotations, which can be easily tuned by external stimuli. H intercalation is favored and promotes the tendency of octahedral rotations.