Boosting Inversion Symmetry Breaking in Epitaxial Tetragonal ZrO2 Via Atomic Layer Deposition

Abstract

The stabilization of intermediate polar phases in fluorite-structured oxides is critical for advancing ferroelectric and antiferroelectric applications. Here, we report the stabilization of epitaxial polar tetragonal (T) ZrO2. Epitaxial HfxZr1-xO2 thin films (x = 1, 0.75, 0.5, 0.25, and 0) are synthesized on (001) yttria-stabilized zirconia substrates via atomic layer deposition. The emergence of the unprecedented polar T-ZrO2 phase deviates from the expected phase transition from nonpolar HfO2 through ferroelectric Hf0.5Zr0.5O2 to antiferroelectric Zr-rich HfxZr1-xO2. Second harmonic generation measurements reveal unexpected inversion symmetry breaking in T-phase ZrO2. High-resolution 4D-scanning transmission electron microscopy further confirms the presence of electric dipoles originating from off-centered oxygen displacements. These findings establish a pathway for the low-temperature epitaxial synthesis of HfO2-ZrO2-based materials and provide critical insight into the polar nature of T-phase ZrO2.