Ferroelectric ZrO2/Hf0.5Zr0.5O2 epitaxial Moiré heterostructures

While oxide heterostructures with emergent properties have garnered a great amount of research interest, heterostructures consisting of oxides with metastable phases have barely been investigated. Here, we fabricated epitaxial bilayer structures based on ZrO2 (ZO) and Hf0.5Zr0.5O2 (HZO) whose single layers, respectively, possess non-polar and polar metastable structures and investigated their structural and ferroelectric properties. We found that the ZO/HZO heterostructures exhibit ferroelectric polarizations comparable to those of HZO films. The bilayer is found to consist of polar orthorhombic lattices with Moiré superlattices, highlighting the key role of the ZO/HZO interfaces in stabilizing the ferroelectricity in the bilayer structures. Furthermore, we found that both the dielectric constant and polarization are increased by reducing the thickness of HZO and ZO layers in the stacked structures and enhancing the interfacial effects.