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

TL;DR

This study uses first-principles simulations to analyze the structural instabilities in infinite-layer nickelates, revealing their tendency for O4 rotations influenced by cation size and external stimuli, with hydrogen intercalation further promoting these distortions.

Contribution

It provides the first detailed analysis of lattice distortions and their tunability in infinite-layer nickelates, highlighting the role of cation size mismatch and external stimuli.

Findings

YNiO₂ exhibits O₄ group rotations influenced by R-to-Ni cation size mismatch.

External pressure or strain can tune the amplitude of these rotations.

Hydrogen intercalation favors octahedral rotations in nickelates.

Abstract

Rare-earth nickelates RNiO$_2$ adopting an infinite-layer phase show superconductivity once La, Pr or Nd are substituted by a divalent cation. Either in the pristine or doped form, these materials are reported to adopt a high symmetry, perfectly symmetric, P4/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 2D nickelates. Here, by performing a full analysis of the prototypical YNiO$_2$ 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.