Metastable Tetragonal BiFeO3Stabilized on Anisotropic a-Plane ZnO

The stabilization of the metastable tetragonal phase of BiFeO3on the highly anisotropic ZnO(11-20) surface is reported. X-ray reciprocal space maps reveal that the BiFeO3layer possesses true tetragonal symmetry rather than the monoclinic MCor MAstructures. Heteroepitaxy generates strongly anisotropic misfit strains of 2.4 and −5.3% along two orthogonal ⟨110⟩ directions of tetragonal BiFeO3. Our analysis shows that such anisotropic strains are very powerful in tailoring the energy balance of competing phases, favoring the formation of tetragonal BiFeO3. Tetragonal BiFeO3can be stabilized on the ZnO template up to a critical thickness of 110 nm, much larger than that of its monoclinic counterparts. The integration of such thick tetragonal BiFeO3films with ZnO has important implications for future applications, as exemplified by the demonstration of a prototype metal/ferroelectric/semiconductor capacitor and the preparation of flexible tetragonal BiFeO3nanomembranes. Additionally, the heteroepitaxial growth was also transposed to the integration of other perovskite oxides with ZnO. Our findings not only shed new light into the strain phase diagram of BiFeO3but also open up a possible avenue toward oxide electronics.