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The atomic-scale structural and electric parameters of the 90° domain-walls in tetragonal ferroelectrics are of technological importance for exploring the ferroelectric switching behaviors and various domain-wall-related novel functions. We have grown epitaxial PbTiO3/SrTiO3 multilayer films in which the electric dipoles at 90° domain-walls of ferroelectric PbTiO3 are characterized by means of aberration-corrected scanning transmission electron microscopy. Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls. The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented. This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

Nanostructured Mn oxide particles with an average size of about 7 nm have been prepared by a microemulsion method. X-ray diffraction analysis indicates that the particles possess orthorhombic structure of MnO(OH). The particles are ferromagnetic at low temperature. The Curie temperature is about 35 K and each MnO(OH) molecule generates a magnetic moment of about 0.7 μB. The appearance of the ferromagnetism at low temperature may result from size effect.

The coupling between antiferrodistortion (AFD) and ferroelectric (FE) polarization, universal for all tilted perovskite multiferroics, is known to strongly correlate with domain wall functionalities in the materials. The intrinsic mechanisms of domain wall phenomena, especially AFD-FE coupling-induced phenomena at the domain walls, have continued to intrigue the scientific and technological communities because of the need to develop the future nano-scale electronic devices. Over the past years, theoretical studies often show controversial results, owing to the fact that they are neither sufficiently nor directly corroborated with experimental evidences. In this work, the AFD-FE coupling at uncharged 180° and 71° domain walls in BiFeO 3 films are investigated by means of aberration-corrected scanning transmission electron microscopy with high resolution (HR-STEM) and rationalized by phenomenological Landau-Ginsburg-Devonshire (LGD) theory. We reveal a peculiar morphology at the AFD-FE walls, including kinks, meandering, triangle-like regions with opposite oxygen displacements and curvature near the interface. The LGD theory confirms that the tilt gradient energy induces these unusual morphology and the features would change delicately with different kinds of domain walls. Moreover, the 180° AFD-FE walls are proved to be conductive with an unexpected reduction of Fe-O-Fe bond angle, which is distinct from theoretical predictions. By exploring AFD-FE coupling at domain walls and its induced functionalities, we provide exciting evidences into the links between structural distortions and its electronic properties, which benefit a lot for fundamental understanding for domain wall functionalities as well as functional manipulations for novel nano-devices.