Ying Liu

The pursuit of ferroelectric materials that combine a high piezoelectric response with robust thermal stability remains a paramount challenge. We introduce a strategy that integrates morphotropic phase boundary (MPB) engineering with high-entropy (HE) design in a novel quinary Pb(Yb_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Fe_1/2Nb_1/2)O₃-PbZrO₃-PbTiO₃ (PYN-PZN-PFN-PZ-PT) perovskite ceramic. Compared to a medium-entropy counterpart, the high-entropy composition yields a superior piezoelectric coefficient of 580 pC/N and exceptional thermal stability, with performance retained up to 285 °C. This enhancement arises from two synergistic effects of the HE design: a stabilized, flattened free-energy landscape that promotes a favorable nanoscale domain structure and improves depolarization behavior, together with higher electrical resistivity (10¹² Ω·cm at 250 °C) arising from HE-driven grain refinement and suppressed charge transport. This work demonstrates that HE design serves as an effective strategy to mitigate the traditional trade-off between piezoelectric response and depolarization temperature in Pb-based relaxor ferroelectrics.

Iron oxides are notable among oxide semiconductors for their abundance and environmental friendliness, positioning Fe₂O₃ as a promising candidate for industrial nanotechnology. However, polymorphic Fe₂O₃ presents up to four phases, posing significant challenges in customizing them for nanocatalysis, including tasking a single phase with complex catalytic reactions, harnessing synergistic advantages during phase integration, and achieving selective reactivity amidst competing side reactions. Here, we developed a 2D-templated Z-direction-confining strategy combined with dual-phase nanocrystallization to synthesize thin-layered Fe₂O₃ with an in-plane nanoscale integration of α- and γ-phases. The resulting dual-phase Fe₂O₃ achieved superior electrochemical nitrate reduction to ammonia, yielding 4329.8 μg/mg_cat/h at -0.8 V vs a reversible hydrogen electrode with high faradaic efficiency (∼95.7%) and outstanding selectivity (99.9%). Combined computational and experimental studies revealed that the enhanced performance arises from the synergistic integration of electron transport through the γ phase and active sites within the α phase, facilitated by ultrafine nanophase domains. Electrons reaching the α phase selectively drive nitrate reduction over proton reduction. The electrocatalyst exhibited exceptional stability across 28 cycles. This catalyst, with its high yield, faradaic efficiency, selectivity, stability, and low cost, outperforms previous catalysts under comparable conditions, highlighting the potential of nanophase manipulation for sustainable ammonia electrosynthesis from nitrate waste.

Ferroelectric materials are characterized by a parallel arrangement of electric dipoles, but at the nanoscale they can present vortices and other non-trivial topological structures^{1,2,3,4,5,6,7,8,9} that combine small size and topological protection, rendering them functionally attractive^10,11,12,13. The driving force for the appearance of vortices in ferroelectrics is the need to minimize the depolarizing fields at interfaces^3,4,5,14; by making the polarization rotate, depolarization fields vanish^4,5,8,9. Antiferroelectrics, by contrast, are defined by an antiparallel arrangement of electric dipoles¹⁵. A priori, therefore, they lack the depolarization fields that drive the appearance of non-trivial topologies in ferroelectrics. At the atomic scale of the dipoles, however, we find that polar discontinuities can still happen, driving the appearance of topological singularities at ferroelastic domain walls.

Antiferroelectrics are materials with an antiparallel but switchable alignment of electric dipoles of equal magnitude so that, in the absence of external voltage, the macroscopic net polarisation is zero. PbZrO ₃ (PZO) was the first material proposed to be antiferroelectric and is regarded as an archetype. Its electric dipoles arrange in a ↑↑↓↓ fashion ( Fig. 1a). Ferrielectric phases, which are closely related to antiferroelectrics and characterized by antiparallel but uncompensated electric dipoles, have attracted considerable attention. In fact, the ground state of PZO has been proposed to be ferrielectric (space group of Ima2 and dipole pattern of ↓↑↓) rather than antiferroelectric.[ 1] The ferrielectric phase represent the lowest-energy state in PZO at 0K and potentially up to room temperature. Using aberration-corrected (scanning) transmission electron microscopy ((S)TEM) methods on a PZO single crystal, we uncover the coexistence of the common antiferroelectric phase and a ferrielectric phase featuring an electric dipole pattern of ↓↑↓. This dipole arrangement, appears at room temperature in the form of translational boundaries ( Fig. 1b− f). In-situ heating and biasing electron microscopy reveal the formation of this ferrielectric phase during cooling from the paraelectric to antiferroelectric phases, and during the ferroelectric-to-antiferroelectric phase transition upon removal of the electric field. [ 2] The electric field induced antiferroelectric to ferroelectric transition is accompanied by significant charge storage, volume expansion, and a temperature drop, making antiferroelectric materials promising for applications in high-density capacitors, high-strain transducers, and electrocaloric cooling. In addition to the electric field induced ferroelectric phase, a ferroelectric phase was also expected in the antiferroelectric PZO ultrathin film, sparking people’s interest in using antiferroelectric materials as an alternative to ferroelectric ones for high-density data storage applications. Fig. 1. (a) A schematic diagram showing two AFE unit cells of PZO. (b-f) The translational boundaries that act as the a ferrielectric phase in antiferroelectric PZO single crystal.

Whereas ferroelectricity may vanish in ultra-thin ferroelectric films, it is expected to emerge in ultra-thin antiferroelectric films, sparking people’s interest in using antiferroelectric materials as an alternative to ferroelectric ones for high-density data storage applications. Lead Zirconate (PbZrO3, PZO) is considered the prototype material for antiferroelectricity, and indeed, previous studies indicated that nanoscale PZO films exhibit ferroelectricity. The understanding of such phenomena from the microstructure aspect is crucial but still lacking. In this study, we fabricated a PZO film with thicknesses varying from 5 to 80 nm. Using Piezoresponse Force Microscopy, we discovered that the film displayed a transition from antiferroelectric behavior in the thicker areas to ferroelectric behavior in the thinner ones, with a critical thickness between 10 and 15 nm. In this critical thickness range, a 12 nm PZO thin film was chosen for further study using aberration-corrected scanning transmission electron microscopy. The investigation showed that the film comprises both ferroelectric and ferrielectric phases. The ferroelectric phase is characterized by polarization along the [011]pc projection direction. The positions of Pb, Zr, and O were determined using the integrated differential phase contrast method. This allowed us to ascertain that the ferroelectric PZO unit cell is half the size of that in the antiferroelectric phase on the ab plane. The observed unit cell is different from the electric field-induced ferroelectric rhombohedral phases. Additionally, we identified a ferrielectric phase with a unique up-up-zero-zero (↑↑··) dipole configuration. The finding is crucial for understanding the performance of ultrathin antiferroelectric thin films and the subsequent design and development of antiferroelectric devices.

The switching dynamics of antiferroelectric lead zirconate (PbZrO₃) freestanding capacitors compared to their epitaxial counterparts is reported. Frequency dependence of hysteresis indicates that freestanding capacitors exhibit a lower dispersion of switching fields, lower residual polarization, and faster switching response as compared to epitaxially‐clamped capacitors. As a consequence, freestanding capacitor membranes exhibit better energy storage density and efficiency.