Role of structure, energetics, and electronic structure in determining the pressure response of octahedral rotations in Ruddlesden-Popper layered perovskites

Octahedral rotations are ubiquitous in perovskite oxides and couple closely to their electronic and magnetic properties. Whereas the pressure response of octahedral rotations in ABO₃ perovskites has been well studied, the impact of pressure on layered perovskites such as the n=2 Ruddlesden-Popper (RP) phase A₃B₂O₇ is much less explored. In this work, we use a combination of group theoretic analysis, density functional theory calculations, and Landau free energy expansions to explore how octahedral rotations in a family of A₃B₂O₇ RP materials respond to applied pressure. Contrasting with the pressure response of octahedral rotations in ABO₃ perovskites, which often can be classified by the charge state of the A- and B-site cations, we find that each A₃²⁺B₂⁴⁺O₇ material that we investigate exhibits a distinct behavior under pressure. We identify the key ingredients that determine the evolution of octahedral rotations in RPs under pressure, and show that it is determined by an interplay of the structural and electronic degrees of freedom. Our results offer insight into how to tune the structure and properties such as ferroelectricity in layered perovskites.