Unlike metals where dislocations carry strain singularity but no charge, dislocations in oxide ceramics are characterized by both a strain field and a local charge with a compensating charge envelope. Oxide ceramics with their deliberate engineering and manipulation are pivotal in numerous modern technologies such as semiconductors, superconductors, solar cells, and ferroics. Dislocations facilitate plastic deformation in metals and lead to a monotonous increase in the strength of metallic materials in accordance with the widely recognized Taylor hardening law. However, achieving the objective of tailoring the functionality of oxide ceramics by dislocation density still remains elusive. Here a strategy to imprint dislocations with {100}<100> slip systems and a tenfold change in dislocation density of BaTiO₃ single crystals using high-temperature uniaxial compression are reported. Through a dislocation density-based approach, dielectric permittivity, converse piezoelectric coefficient, and alternating current conductivity are tailored, exhibiting a peak at medium dislocation density. Combined with phase-field simulations and domain wall potential energy analyses, the dislocation-density-based design in bulk ferroelectrics is mechanistically rationalized. These findings may provide a new dimension for employing plastic strain engineering to tune the electrical properties of ferroics, potentially paving the way for advancing dislocation technology in functional ceramics.

The pinning-controlled mobility of ferroelectric/ferroelastic domain walls is an important part of managing polarization switching and determining the final properties of ferroelectric and piezoelectric materials. Here, we assess the impact of temperature on dislocation-induced domain wall pinning as well as on dislocation-tuned dielectric and piezoelectric response in barium titanate single crystals. Our solid-state nuclear magnetic resonance spectroscopy results indicate that the entire sample exclusively permits in-plane domains, with their distribution remaining insensitive to temperature changes below the Curie temperature (T_C). The domain wall pinning field monotonically decreases with increasing temperature up to T_C, as evidenced by a combination of experimental observations and phase-field simulations. Our work highlights the promising potential of dislocation engineering in controlling domain wall mobility within bulk ferroelectrics.

We report an intrinsic strain engineering, akin to thin filmlike approaches, via irreversible high-temperature plastic deformation of a tetragonal ferroelectric single-crystal BaTiO3. Dislocations well-aligned along the [001] axis and associated strain fields in plane defined by the [110]/[1¯10] plane are introduced into the volume, thus nucleating only in-plane domain variants. By combining direct experimental observations and theoretical analyses, we reveal that domain instability and extrinsic degradation processes can both be mitigated during the aging and fatigue processes, and demonstrate that this requires careful strain tuning of the ratio of in-plane and out-of-plane domain variants. Our findings advance the understanding of structural defects that drive domain nucleation and instabilities in ferroic materials and are essential for mitigating device degradation.

Defects are essential to engineering the properties of functional materials ranging from semiconductors and superconductors to ferroics. Whereas point defects have been widely exploited, dislocations are commonly viewed as problematic for functional materials and not as a microstructural tool. We developed a method for mechanically imprinting dislocation networks that favorably skew the domain structure in bulk ferroelectrics and thereby tame the large switching polarization and make it available for functional harvesting. The resulting microstructure yields a strong mechanical restoring force to revert electric field–induced domain wall displacement on the macroscopic level and high pinning force on the local level. This induces a giant increase of the dielectric and electromechanical response at intermediate electric fields in barium titanate [electric field–dependent permittivity (e₃₃) ≈ 5800 and large-signal piezoelectric coefficient (d₃₃*) ≈ 1890 picometers/volt]. Dislocation-based anisotropy delivers a different suite of tools with which to tailor functional materials.

Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST) core–shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core–shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion.