Discovery of a new weberite-type antiferroelectric: La3NbO7

TL;DR

This study demonstrates the discovery of a new lead-free weberite-type antiferroelectric, La3NbO7, by integrating large-scale first-principles phonon screening with experimental verification. A Kittel-like, single-mode antipolar switching mechanism yields an antipolar ground state with minimal volume change, and La3NbO7 exhibits a high threshold field together with a high breakdown field, making it a promising candidate for energy storage. The work further uncovers a broader A3MO7 weberite-family landscape with tunable properties via rare-earth and B-site substitutions, representing a data-driven theory-to-experiment blueprint for designing ferroic materials. Collectively, the results expand the ferroic materials palette beyond perovskites and highlight practical routes to tailor transition temperatures and fields in AFEs.

Abstract

Antiferroelectrics are antipolar materials which possess an electric field-induced phase transition to a polar, ferroelectric phase and offer significant potential for sensing/actuation and energy-storage applications. Known antiferroelectrics are relatively scarce and mainly based on a limited set of perovskite materials and their alloys (e.g., PbZrO$_3$, AgNbO$_3$, NaNbO$_3$). Here, a new family of lead-free, weberite-type antiferroelectrics, identified through a large-scale, first-principles computational search is introduced. The screening methodology, which connects lattice dynamics to antipolar distortions, predicted that La$_3$NbO$_7$ could exhibit antiferroelectricity. We confirm the prediction through the synthesis and characterization of epitaxial La$_3$NbO$_7$ thin films, which display the signature double hysteresis loops of an antiferroelectric material as well as clear evidence of an antipolar ground state structure from transmission electron microscopy. The antiferroelectricity in La$_3$NbO$_7$ is simpler than most known antiferroelectrics and can be explained by a Kittel-type mechanism involving the movement of niobium atoms in an oxygen octahedron through a single phonon mode which results in a smaller change in the volume during the field-induced phase transition. Additionally, it is found that La$_3$NbO$_7$ combines a high threshold field with a high breakdown field ($\approx$ 6MV/cm) - which opens up opportunities for energy-storage applications. This new weberite-type family of materials offers many opportunities to tune electrical and temperature response especially through substitutions on the rare-earth site. Ultimately, this work demonstrates a successful data-driven theory-to-experiment discovery of an entirely new family of antiferroelectrics and provides a blueprint for the future design of ferroic materials.

Figures (16)

• Figure 1: Schematic representation of the phonon band structures and the expected ground states for (A) a paraelectric material showing no instabilities and preserving a centrosymmetric structure, (B) a ferroelectric material with a dominant instability at $\Gamma$ and exhibiting a ferrodistortive pattern of distortion, and (C) an AFE material in which the dominant instability is found at a zone-boundary and thus, showing antipolar distortion. The arrows represents the atomic displacements which coincides with the local dipole moments. A perovskite-like crystal structure has been chosen for illustrative purposes. This represents an idealized case where the dominant instability leads to the energy ground-state. However, it is possible that the condensation of the mode with the largest imaginary frequency does not lead to the energy ground state.
• Figure 2: Energy difference between the parent and AFE phase $\Delta E_{parent}$ (in meV/atom) versus threshold field $E_{th}$ (in MV/cm) for all AFE candidates identified through our high-throughput screening as well as for two prototypical AFEs (PZO and ANO). All calculations have been performed using PBEsol. The color and markers indicate different chemistry and classes of materials.
• Figure 3: (A) Parent structure of La3NbO7, which is paraelectric and belongs to the Cmcm space group. The NbO6 octahedra are shown in dark green while we distinguish the layers of 4a (light gold) and 8g (dark gold) lanthanum atoms. (B) Phonon band structure of La3NbO7. The main instabilities are found at $\Gamma$ and $Y$, with the latter being slightly more negative (imaginary). (C) Structures of the AFE (Pnma), FE (Cmc2$_1$) and PE (Cmcm) phases of La3NbO7 and their respective energies. The displacements of the atoms in the AFE and FE phases with respect to the PE phase are shown by dark arrows.
• Figure 4: X-ray- and transmission electron microscopy (TEM)-based diffraction measurements from La3NbO7 films. a. X-ray $\theta$-2$\theta$ linescans show films are predominately (011)-oriented, while b.$\phi$-scans establish the epitaxy with the underlying (pseudo)subic LSMO electrode and SrTiO3 substrate, where c. an approximately square lattice is formed on the La3NbO7 (011) interface whose lattice parameter is relatively close to d. that of LSMO strained to SrTiO3. e. 4D-STEM nanobeam diffraction demonstrates obvious 1/2-order spots which agree with f. the simulated electron diffraction pattern of the AFE [111] zone axis and are distinct from the alternative g. FE [021] and h. PE [201] zone axes.
• Figure 5: Capacitor-device-based a. dielectric constant and b. loss tangent versus DC electric field and c. polarization (left axis) and current (right axis) versus electric field measured at 10 kHz. All measurements demonstrate strong indications of the expected AFE nature, with double peaks in capacitance measurements, double hysteresis in polarization, and four peaks in current response.