Harnessing Phase Transitions in Antiferroelectric ZrO2 Using the Size Effect

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 ZrO2 is of particular technological interest, but the origin of antiferroelectricity in ZrO2 remains questionable. The theory of reversible electric field-induced phase transitions between the nonpolar P4(2)/nmc tetragonal phase and the polar Pca2(1) orthorhombic phase is experimentally tested with local structural and electromechanical characterization of AFE ZrO2 thin films. Piezoresponse force microscopy identifies signature evidence of a field-induced phase transition. A significant size effect in AFE ZrO2 is 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(-1) depending on crystallite size and in-plane compressive strain with decreasing ZrO2 film thickness. Using the size effect, it is possible to double the energy storage density in ZrO2 from 20 J cm(-3) to greater than 40 J cm(-3), thus highlighting a feasible route for superior performance in AFE fluorite supercapacitors.