Aberration-Corrected Transmission Electron Microscopy Reveals Nanoscale Disorder in Bismuth Ferrite Single Crystals

In recent years, in particular after it was demonstrated [2] that thin epitactic films of BFO display extraordinary high values of spontaneous electric polarization, the work on electric and magnetic properties and their coupling concentrated on thin film systems. Also the structure of polarization-domain walls in these films was studied by transmission electron microscopy [e.g. 3-6]. In our work we followed an entirely different approach. It is generally accepted that for a study of the basic, intrinsic physical properties of a material single crystals are required. In fact, compared to thin films there is comparatively little work done on BFO single crystals. And in spite of more than thirty years of BFO research, until recently [7] there was not a single study on single crystals by electron microscopy. Here we give a brief account of the first results obtained on single crystals by aberration-corrected TEM [8]. Our study is typical for the high potential of aberration-corrected high-resolution TEM in the field of modern materials science where structures of atomicto nanoscale may be decisive for physical properties but are not always noticed by non-local techniques.