Ferroelectric materials are of extreme interest for applications, such as the active layer in non-volatile memory devices, biomedical ultrasound imaging and MEMS. A successful integration of miniaturized ferroelectrics, such as nanoparticles is required for advancing future technologies. However, as the crystal dimensions of a ferroelectric is reduced below a certain size, a well-documented ’size effect‘ makes a non-ferroelectric cubic phase favorable over the tetragonal ferroelectric phase. This size effect encumbers practical realization of ferroelectric nanomaterials in advancing technologies. The origin of the threshold size is still not clearly understood, mainly because of the limited available experimental observation of the phenomenon. We set to investigate the phase transition at crystals of a few tens to a few hundreds of nm in size.
In-situ TEM imaging during the ferroelectric phase change is an ideal method for understanding the macro- and nano- scale changes occurring in the material. Aside from highlighting different crystal phases in the material with diffraction contrast, TEM imaging is sensitive to different poling directions in the crystal. This way one can obtain an insight into the dynamics of the ferroelectric domain formation (e.g. nucleation) and growth mechanism.
BaTiO3 is a seminal ferroelectric material, with a bulk phase transition as low as 130°C and thus is an excellent model system. We used high-resolution TEM equipped with high-angle annular dark-field (HAADF) detector for in-situ direct observation of the collective ion behavior at the domain wall and nucleation sites around the phase transition of BTO nanoparticles. Our work is expected to give a prefund understanding of the BaTiO3collective ionic re-organization around phase changes, leading potentially, at last to successful future integration of nano-ferroelectric particles in next-generation technologies.
