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Crystalline materials with broken inversion symmetry can exhibit a spontaneous electric polarization, which originates from a microscopic electric dipole moment. Long-range polar or anti-polar order of such permanent dipoles gives rise to ferroelectricity or antiferroelectricity, respectively. However, the recently discovered antiferroelectrics of fluorite structure (HfO₂and ZrO₂) are different: A non-polar phase transforms into a polar phase by spontaneous inversion symmetry breaking upon the application of an electric field. Here, we show that this structural transition in antiferroelectric ZrO₂gives rise to a negative capacitance, which is promising for overcoming the fundamental limits of energy efficiency in electronics. Our findings provide insight into the thermodynamically forbidden region of the antiferroelectric transition in ZrO₂and extend the concept of negative capacitance beyond ferroelectricity. This shows that negative capacitance is a more general phenomenon than previously thought and can be expected in a much broader range of materials exhibiting structural phase transitions.

Antiferroelectric materials, where the transition between antipolar and polar phase is controlled by external electric fields, offer exceptional energy storage capacity with high efficiencies, giant electrocaloric effect, and superb electromechanical response. PbZrO₃is the first discovered and the archetypal antiferroelectric material. Nonetheless, substantial challenges in processing phase pure PbZrO₃have limited studies of the undoped composition, hindering understanding of the phase transitions in this material or unraveling the controversial origins of a low‐field ferroelectric phase observed in lead zirconate thin films. Leveraging highly oriented PbZrO₃thin films, a room‐temperature ferrielectric phase is observed in the absence of external electric fields, with modulations of amplitude and direction of the spontaneous polarization and large anisotropy for critical electric fields required for phase transition. The ferrielectric state observations are qualitatively consistent with theoretical predictions, and correlate with very high dielectric tunability, and ultrahigh strains (up to 1.1%). This work suggests a need for re‐evaluation of the fundamental science of antiferroelectricity in this archetypal material.

“Anode‐free” solid‐state batteries (SSBs), which have no anode active material, can exhibit extremely high energy density (≈1500 Wh L⁻¹). However, there is a lack of understanding of the lithium plating/stripping mechanisms at initially lithium‐free solid‐state electrolyte (SSE) interfaces because excess lithium metal is often used. Here, it is demonstrated that commercially relevant quantities of lithium (>5 mAh cm⁻²) can be reliably plated at moderate current densities (1 mA cm⁻²) using the sulfide SSE Li₆PS₅Cl. Investigations of lithium plating/stripping mechanisms, in conjunction with cryo‐focused ion beam (FIB) imaging, synchrotron tomography, and phase‐field modeling, reveal that the cycling stability of these cells is fundamentally limited by the nonuniform presence of lithium during stripping. Local lithium depletion causes isolated lithium regions toward the end of stripping, decreasing electrochemically active area and resulting in high local current densities and void formation. This accelerates subsequent filament growth and short circuiting compared to lithium‐excess cells. Despite this degradation mode, it is shown that anode‐free cells exhibit comparable Coulombic efficiency to lithium‐excess cells, and improved resistance to short circuiting is achieved by avoiding local lithium depletion through retention of thicker lithium at the interface. These new insights provide a foundation for engineering future high‐energy anode‐free SSBs.

Originally based on phenomenological observations, the Janovec–Kay–Dunn (JKD) scaling law has been historically used to describe the dependence of the ferroelectric coercive fields (E_c) on a critical length scale of the material, wherein the film thickness (t) is considered the length scale, andE_c∝t^−2/3. Here, for the first time, a JKD‐type scaling behavior is reported in an antiferroelectric material, using the ultra‐thin films of prototypical flourite‐structure binary oxide, zirconia. In these films, a decrease in the ZrO₂layer thickness from 20 nm to 5.4 nm leads to an increase in critical fields for both nonpolar‐to‐polar (E_a), and polar‐to‐nonpolar (E_f) transitions, accompanied by a decrease in the average crystallite size, and an increase in the tetragonal distortion of the non‐polarP4₂/nmcground state structure. Notably, the ‐2/3 power law as in the JKD law holds when average crystallite size (d), measured from glancing‐incident X‐ray diffraction, is considered as the critical length scale—i.e.,E_a,E_f∝d^−2/3. First principles calculations suggest that the increase of tetragonality in thinner films contributes to an increase of the energy barrier for the transition from the non‐polar tetragonal ground state to the field‐induced polar orthorhombic phase, and in turn, an increase inE_acritical fields. These results suggest a de‐stabilization of the ferroelectric phase with a decreasing thickness in antiferroelectric ZrO₂, which is contrary to the observations in its fluorite‐structure ferroelectric counterparts. With the recent interests in utilizing antiferroelectricity for advanced semiconductor applications, our fundamental exposition of the thickness dependence of functional responses therein can accelerate the development of miniaturized, antiferroelectric electronic memory elements for the complementary metal‐oxide‐semiconductor based high‐volume manufacturing platforms.