We show that in contrast to the conventional view of a mean-field Landau-type behavior, the oxygen octahedral tilt $\left(R\right)$ and polarization $\left(P\right)$ in the $A_3{B}_2{\mathrm{O}}_7$ Ruddlesden-Popper hybrid improper ferroelectric ${(\mathrm{Ca},\mathrm{Sr})}_3{\mathrm{Ti}}_2{\mathrm{O}}_7$ exhibits the scaling behavior of a 2D Ising class near the para-to-ferroelectric transition temperature ($T_{\mathrm{c}}$). We also show that $P$ exhibits an additional transition from a 2D Ising to a 3D mean-field critical behavior at a temperature $T_{\mathrm{d}}<T_{\mathrm{c}}$, which is driven by enhanced interlayer dipolar correlations due to an increase in the ferroelectrically active $B$-site centered dipoles.

• Received 18 November 2022
• Revised 15 May 2023
• Accepted 24 May 2023

DOI:https://doi.org/10.1103/PhysRevB.107.224103