Oxygen octahedral tilts underpin the functionality of a large number of perovskite-based materials and heterostructures with competing order parameters. We show how a precise analysis of atomic column shapes in Z-contrast scanning transmission electron microscopy images can reveal polarization and octahedral tilt behavior across uncharged and charged domain walls in BiFeO(3). This method is capable of visualizing octahedral tilts to much higher thicknesses than phase contrast imaging. We find that the octahedral tilt transition across a charged domain wall is atomically abrupt, while the associated polarization profile is diffuse (1.5-2 nm). Ginzburg-Landau theory then allows the relative contributions of polarization and the structural order parameters to the wall energy to be determined.

The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots. Strain in epitaxial oxide films has become a universally recognized method for tuning materials properties [1][2][3], enabling novel couplings between magnetic, lattice, and strain behaviors [4][5][6], stabilizing new phases [7] or domain morphologies [8]. Systematic studies of a material's response to strain enable exploration of the fundamental mechanisms responsible for, e.g., the ferroelectric instability [9][10][11][12].While strain effects on intrinsic properties [9,12] and domain morphologies [13,14] are readily amenable to theoretical and experimental studies, their role on local and emergent properties [15] in disordered materials, including polycrystalline ferroelectric films and relaxors, remains virtually unexplored [16,17], Indeed, many of these materials exhibit unique physical properties including giant electromechanical coupling coefficients, broad dispersions of dielectric permittivity, etc. [18][19][20][21]. These phenomena are often associated with the presence of nanoscale textures of domains or nanoscale phase separation [22][23][24]. In all these materials, the dominant order parameter is either strain (ferroelastics) or is strongly coupled to strain (relaxors, morphotropic systems), suggesting the significant role of frustrated or random strain interactions [25][26][27]. Correspondingly, tuning mechanical boundary conditions can significantly affect emergent behaviors in disordered ferroics and provide insight into corresponding coupling mechanisms.Here, we aim to explore domain wall dynamics as reflected in ferroelectric nonlinearities in model PbZr 0:52 Ti 0:48 O 3 thin films. In polycrystalline lead zirconate-titanate (PZT) ceramics, domain wall motion may contribute more than 50% of the dielectric and piezoelectric properties at room temperature [23,28]. However, in thin films these extrinsic contributions to the piezoelectric response can be severely limited by several factors, including substrate clamping [29]. Recent spatially resolved studies of piezoelectri...

The atomic-level sculpting of 3D crystalline oxide nanostructures from metastable amorphous films in a scanning transmission electron microscope (STEM) is demonstrated. Strontium titanate nanostructures grow epitaxially from the crystalline substrate following the beam path. This method can be used for fabricating crystalline structures as small as 1-2 nm and the process can be observed in situ with atomic resolution. The fabrication of arbitrary shape structures via control of the position and scan speed of the electron beam is further demonstrated. Combined with broad availability of the atomic resolved electron microscopy platforms, these observations suggest the feasibility of large scale implementation of bulk atomic-level fabrication as a new enabling tool of nanoscience and technology, providing a bottom-up, atomic-level complement to 3D printing.

The rich functionalities in the ABO3 perovskite oxides originate, at least in part, from the ability of the corner-connected BO6 octahedral network to host a large variety of cations through distortions and rotations. Characterizing these rotations, which have significant impact on both fundamental aspects of materials behavior and possible applications, remains a major challenge at heterointerfaces. In this work, we have developed a unique method to investigate BO6 rotation patterns in complex oxides ABO3 with unit cell resolution at heterointerfaces, where novel properties often emerge. Our method involves column shape analysis in ABF-STEM images of the ABO3 heterointerfaces taken in specific orientations. The rotating phase of BO6 octahedra can be identified for all three spatial dimensions without the need of case-by-case simulation. In several common rotation systems, quantitative measurements of all three rotation angles are now possible. Using this method, we examined interfaces between perovskites with distinct tilt systems as well as interfaces between tilted and untilted perovskites, identifying an unusual coupling behavior at the CaTiO3/LSAT interface. We believe this method will significantly improve our knowledge of complex oxide heterointerfaces.