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) ZrO(2). Epitaxial Hf(x)Zr(1-x)O(2) 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-ZrO(2) phase deviates from the expected phase transition from nonpolar HfO(2) through ferroelectric Hf(0.5)Zr(0.5)O(2) to antiferroelectric Zr-rich Hf(x)Zr(1-x)O(2). Second harmonic generation measurements reveal unexpected inversion symmetry breaking in T-phase ZrO(2). 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 HfO(2)-ZrO(2)-based materials and provide critical insight into the polar nature of T-phase ZrO(2).