Engineering of Crystal and Domain Structures in Epitaxial Y:HfO₂ Thin Films by YSZ Substrate Miscut

The crystal and domain structures of epitaxial polymorphic oxide thin films are governed not only by intrinsic bulk energies but also by extrinsic factors arising from interactions with the underlying oxide substrates. Here, we investigate the effects of substrate miscut on the phase stability of epitaxial HfO₂ films on yttria-stabilized zirconia (Y:ZrO₂, YSZ), employing a combined experimental and computational approach to map the thickness-temperature phase diagram. High-quality epitaxial 6% Y-doped HfO₂ films with atomically smooth surfaces were fabricated by magnetron sputtering on both nominally-flat and 8°-miscut (001) YSZ single-crystal substrates. On nominally-flat substrates, (100)-oriented orthorhombic films form a two-variant domain structure and evolve into (001)-oriented monoclinic phases at larger thicknesses. On 8°-miscut substrates, in contrast, a (100)-oriented orthorhombic phase with a preferential population among the two variants is stabilized at small thicknesses, whereas a reoriented, (100)-oriented monoclinic phase is favored at larger thicknesses, accompanied by a pronounced narrowing of the orthorhombic stability window. This work provides fundamental insight into the control of phase stability and domain architecture in polymorphic oxides, relevant to the integration of complex oxides in advanced electronic platforms.