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Abstract The unique nonlinear dielectric properties of antiferroelectric (AFE) oxides are promising for advancements in solid state supercapacitor, actuator, and memory technologies. AFE behavior in high‐k ZrO₂is of particular technological interest, but the origin of antiferroelectricity in ZrO₂remains questionable. The theory of reversible electric field‐induced phase transitions between the nonpolar P4₂/nmc tetragonal phase and the polarPca2₁orthorhombic phase is experimentally tested with local structural and electromechanical characterization of AFE ZrO₂thin films. Piezoresponse force microscopy identifies signature evidence of a field‐induced phase transition. A significant size effect in AFE ZrO₂is experimentally observed as film thickness is scaled down from 14.7 to 4.3 nm. The size effect is explained by modifications to the phase transition energy barrier heights ranging from 0.6 to 7.6 meV f.u⁻¹depending on crystallite size and in‐plane compressive strain with decreasing ZrO₂film thickness. Using the size effect, it is possible to double the energy storage density in ZrO₂from 20 J cm⁻³to greater than 40 J cm⁻³, thus highlighting a feasible route for superior performance in AFE fluorite supercapacitors. 

Abstract Knowledge about phase transitions in doped HfO₂and ZrO₂‐based films is crucial for developing future ferroelectric devices. These devices should perform in ambient temperature ranges with no degradation of device performance. Here, the phase transition from the polar orthorhombic to the nonpolar tetragonal phase in thin films is of significant interest. Detailed electrical and structural characterization is performed on 10 nm mixed Hf_xZr_1‐xO₂binary oxides with different ZrO₂in HfO₂and small changes in oxygen content. Both dopant and oxygen content directly impact the phase transition temperature between the polar and nonpolar phase. A first‐order phase transition with thermal hysteresis is observed from the nonpolar to the polar phase with a maximum in the dielectric constant. The observed phase transition temperatures confirm trends as obtained by DFT calculations. Based on the outcome of the measurements, the classification of the ferroelectric material is discussed.