Turning ABO$_3$ antiferroelectrics into ferroelectrics: Design rules for practical rotation-driven ferroelectricity in double perovskites and A$_3$B$_2$O$_7$ Ruddlesden-Popper compounds

Abstract: Ferroic transition metal oxides, which exhibit spontaneous elastic, electrical, magnetic or toroidal order, exhibit functional properties that find use in ultrastable solid-state memories to sensors and medical imaging technologies. To realize multifunctional behavior, where one order parameter can be coupled to the conjugate field of another order parameter, however, requires a common microscopic origin for the long-range order. Here, we formulate a complete theory for a novel form of ferroelectricity, whereby a spontaneous and switchable polarization emerges from the destruction of an antiferroelectric state due to octahedral rotations and ordered cation sublattices. We then construct a materials design framework based on crystal-chemistry descriptors rooted in group theory, which enables the facile design of artificial oxides with large electric polarizations, P, simultaneous with small energetic switching barriers between +P and -P. We validate the theory with first principles density functional calculations on more than 16 perovskite-structured oxides, illustrating it could be operative in any materials classes exhibiting two- or three-dimensional corner-connected octahedral frameworks. We show the principles governing materials selection of the "layered" systems originate in the lattice dynamics of the A cation displacements stabilized by the pervasive BO$_6$ rotations of single phase ABO$_3$ materials, whereby the latter distortions govern the optical band gaps, magnetic order and critical transition temperatures. Our approach provides the elusive route to the ultimate multifunctionality property control by an external electric field.

• The paper introduces a mechanism for inducing ferroelectricity in antiferroelectric perovskites via octahedral rotations and cation ordering.
• It establishes a predictive design framework using crystal-chemistry descriptors and validates the approach with density functional theory across multiple oxides.
• The study offers practical insights for engineering low-barrier, switchable ferroelectrics for advanced electronic applications.

Design Principles for Rotation-Driven Ferroelectricity in Perovskite Oxides

The research paper proposes a theoretical and computational framework for designing ferroelectric materials from antiferroelectric perovskite oxides. The work focuses on ABO$_3$ antiferroelectrics, suggesting a mechanism to induce ferroelectricity through octahedral rotations and cation ordering. Leveraging group theory and density functional theory (DFT), the study establishes a structured approach to engineer and predict ferroelectric properties in perovskite-structured oxides, emphasizing rotational distortions and their coupling with polarization.

Key Contributions

1. Novel Ferroelectricity Mechanism: The paper introduces a mechanism for ferroelectricity driven by octahedral rotations in perovskites and Ruddlesden-Popper phases. This involves the disruption of an antiferroelectric state to induce a spontaneous and switchable polarization, a process mediated by the rotations of the BO$_6$ octahedra and ordered A-cation sublattices.
2. Design Framework: By utilizing crystal-chemistry descriptors, such as tolerance factors, and symmetry considerations, a predictive design framework is established. It allows for the transformation of non-polar perovskites into ferroelectrics by designing materials with specific rotational characteristics and lattice dynamics.
3. Density Functional Theory Validation: The theoretical predictions are substantiated through DFT calculations across various perovskite oxides, demonstrating the viability of the design rules in practice and underscoring the correlation between experimental observations and theoretical insights.

Numerical Results and Analysis

• The study conducts DFT calculations on over 16 perovskite oxides, offering insights into the relationship between octahedral rotations, spontaneous polarization, and switching barriers.
• It is identified that polarization, $P$, increases with larger rotations ($Q_{R1}$, $Q_{R2}$), as expressed by the hybrid improper ferroelectricity (HIF) mechanism through the trilinear coupling in the free energy.

Theoretical Implications

The research suggests that the proposed mechanism is applicable to any material class featuring corner-connected octahedral frameworks. It hints at broader implications for the development of multifunctional materials wherein electric fields can control various macroscopic properties due to the intimate coupling of polarization with rotations and cation orderings.

Future Directions

The findings encourage further exploration of low-barrier ferroelectrics that are accessible through targeted chemical adjustments, promoting the widespread use of such materials in advanced electronic and spintronic applications. Future efforts should focus on experimental validation of these predictions and on the design of materials with even more intricate properties by manipulating chemical and structural aspects guided by the proposed framework.

In conclusion, this study significantly advances the understanding of ferroelectricity in complex oxides and provides a methodical blueprint for designing new materials with desired electro-mechanical properties. The implications for theoretical exploration and practical applications, particularly in the development of novel electronic devices, are profound.