Ferroelectric Domain Structures in Low-Strain BaTiO3

Epitaxial strain in ferroelectric films offers the possibility to enhance the piezoelectric performance utilizing low crystal symmetries and high density of domain walls. Ferroelectric BaTiO3 has been predicted to order in a variety of phases and domain configurations when grown under low strain on low mismatched substrates, but little experimental evidence of that region of the phase diagram exist. Here, epitaxial BaTiO3 thin films are grown on NdScO3 substrates under approximate to 0.1% strain. A monoclinic ca(1)/ca(2) phase, with 90 degrees periodic in-plane domain configuration and small additional out-of-plane component of polarization, is stabilized at room temperature and investigated using piezoelectric force microscopy and X-ray diffraction. Above 50 degrees C, this phase is transformed into an a/c phase with alternating in-plane and out-of-plane polarizations and forming zigzag domain walls between up-polarized and down-polarized superdomains. Both types of domain patterns are highly anisotropic, giving rise to very long domain walls. Above 130 degrees C, the paraelectric phase is observed. The occurrence of a phase transition close to room temperature, a low symmetry ca(1)/ca(2) phase, and the formation of periodic domains make of this material a promising candidate for high piezoelectric response.