Impact of octahedral rotations on Ruddlesden-Popper phases of antiferrodistortive perovskites

TL;DR

This study provides a detailed theoretical analysis of how oxygen octahedral rotations influence the stability and structure of Ruddlesden-Popper phases in antiferrodistortive perovskites, revealing key interactions affecting phase behavior.

Contribution

It offers the most comprehensive theoretical investigation to date of octahedral rotation effects on RP phases in AFD perovskites, including asymptotic behavior and interaction mechanisms.

Findings

Inverse-distance interaction between stacking faults

Octahedral rotations can stabilize or destabilize RP phases

Rotational states are constrained by oxygen ion distances

Abstract

This work presents the most detailed and extensive theoretical study to date of the structural configurations of Ruddlesden-Popper (RP) phases in antiferrodistortive (AFD) perovskites and formulates a program of study which can be pursued for RP phases of any AFD perovskite system. We systematically investigate the effects of oxygen octahedral rotations on the energies of RP phases in AFD perovskites (A_n+1 B_n O_3n+1) for n = 1...30, providing asymptotic results for n --> infinity that give both the form of the interaction between stacking faults and the behavior of such stacking faults in isolation. We find an inverse-distance interaction between faults with a strength which varies by as much as a factor of two depending on the configuration of the octahedra. We find that the strength of this effect can be sufficient to (a) stabilize or destabilize the RP phase with respect to dissociation into the bulk perovskite and the bulk A-oxide and (b) affect the energy scales of the RP phase sufficiently to constrain the rotational states of the octahedra neighboring the stacking faults, even at temperatures where the octahedra in the bulk regions librate freely. Finally, we present evidence that the importance of the octahedral rotations can be understood in terms of changes in the distances between oxygen ions on opposing sides of the RP stacking faults.