Strategy to utilize transmission electron microscopy and X-ray diffraction to investigate biaxial strain effect in epitaxial BiFeO_3 films

摘要

The recent resurgence of bismuth ferrite (BiFeO3) as a multiferroic material was triggered by the revelation of its true bulk physical properties in the mid 2000s. Subsequently, multiferroic properties of BiFeO3 have been found to improve when it is grown as epitaxial film owing to the biaxial strain imposed by substrate materials. Since the crystal and microstructural modifications caused by the strain dominate the multiferroic property changes in BiFeO3, tremendous efforts have been devoted to the investigation of structural changes in epitaxial BiFeO3 films. However, details about strain-induced structural modifications remain elusive owing to the remarkably complex nature of BiFeO3. In this review, we discuss the followings: (1) what are the pros and cons between transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques, (2) a noble methodology of how to apply TEM and XRD to unambiguously identify crystal symmetries in epitaxial BiFeO3, and (3) once crystal symmetries are clearly identified, how can the misfit strain be accurately evaluated. (C) 2018 The Japan Society of Applied Physics