Direct Visualization of Distorted Twin Boundaries in Ce-Doped GdFeO₃

Utilizing advanced transmission electron microscopy (TEM), the structure at the (110)-type twin boundary (TB) of Ce-doped GdFeO₃ (C-GFO) has been investigated with picometer precision. Such a TB is promising to generate local ferroelectricity within a paraelectric system, while precise knowledge about its structure is still largely missing. In this work, a direct measurement of the cation off-centering with respect to the neighboring oxygen is enabled by integrated differential phase contrast (iDPC) imaging, and up to 30 pm Gd off-centering is highly localized at the TB. Further electron energy loss spectroscopy (EELS) analysis demonstrates a slight accumulation of oxygen vacancies at the TB, a self-balanced behavior of Ce at the Gd sites, and a mixed occupation of Fe²⁺ and Fe³⁺ at the Fe sites. Our results provide an informative picture with atomic details at the TB of C-GFO, which is indispensable to further push the potential of grain boundary engineering.