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BaTiO3 (BT), a lead‐free ferroelectric material, is employed in energy‐conversion devices, including actuators and capacitors. However, its ferroelectric properties, such as the piezoelectric coefficient and Curie temperature, fall short of those of harmful lead‐based ferroelectrics, such as Pb(Zrx, Ti1−x)O3. In this study, a BT crystal is examined under biaxial strain (i.e., strain in the a‐ and b‐directions of the unit cell) to investigate the alterations in its ferroelectric properties. The piezoelectric coefficient, Curie temperature, polarization magnitude, and coercive electric field are calculated under varying biaxial strains using molecular dynamics simulations. The simulations utilize a core–shell‐type interatomic potential developed from first‐principles electronic structure calculations. In the findings, it is revealed that 1) the Curie temperature, polarization magnitude, and coercive electric field increase, whereas the piezoelectric coefficient in the c‐direction decreases under biaxial compression; 2) modifications in the ferroelectric properties depend on the area of ab‐plane and not on its aspect ratio. Comprehensive analyses of the Ti‐displacement distribution offer microscopic insights into strain‐induced shifts in ferroelectric properties. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3) is a ferroelectric material without toxic elements, whose ferroelectric properties such as permittivity, coercive field, and spontaneous polarization are affected by the nucleation of domains of reversed polarization and the motion of domain walls. Dislocations can act as obstacles to domain‐wall migration or as active sites for domain nucleation. Thus, studies are conducted on the utilization of dislocations to improve the ferroelectric properties of BaTiO3. However, the atomistic mechanism of domain nucleation around the dislocation core is still unclear. In this article, a machine learning (ML) potential is developed to study the influence of dislocations on domain nucleation. The potential is trained using an active‐learning approach to ensure accuracy in the bulk properties of the ferroelectric and paraelectric phases, as well as in the dislocation core structures in BaTiO3. Molecular dynamics simulations using the ML potential show that the influence of dislocations on polarization reversal depends on the directional relationship between the external electric field and the dislocation. Furthermore, strong local polarizations exist surrounding the dislocation core, owing to vacancies in the core. These polarizations can act as both domain nucleation sites and obstacles for domain migration when ordered along the dislocation line. [ABSTRACT FROM AUTHOR]

BaTiO3 is a well-known piezoelectric material with commercial uses. The ferroelectric state of BaTiO3 generally comprises electrically polarized domains separated by domain walls (DWs). The DW alters local polarization vectors by an angle of 90° for 90° DW or 180° for 180° DW. The DW is crucial to piezoelectric properties such as response time and fatigue. Furthermore, the DW structure and its dynamics in BaTiO3 are not well understood. Hence, for the first time, we theoretically obtained the atomistic structure of the 90° DW via molecular dynamics simulations at 300 K with the core–shell interatomic potential, using a large-scale system with a side length of 2.8 × 10 3 Å. The width of the 90° DW thereby obtained was approximately 30 Å, which was 20 Å wider than that of the 180° DW. Under the external electric field E → ext parallel to the DW, we observed an extension of a domain having a polarization vector with a positive component along the E → ext -direction. The migration velocity of the 90° DW was approximately two times that of the 180° DW at the same E ext in the range 7 – 20 MV / m. For E ext ≥ 15 MV / m , the migration velocity of the 90° DW in the direction with a positive component along the polarization vector of the extending domain was substantially higher than that in the opposite direction. The physical causes of the difference in the migration velocities of the 90° DW in the two directions were analyzed. [ABSTRACT FROM AUTHOR]

Polarization switching in ferroelectric hysteresis of BaTiO3 proceeds by localized nucleation and subsequent growth of domains of reverse polarization. While this process is driven by the applied electric field, thermal activation can play an important role in domain nucleation. As a consequence of the stochastic nature of thermal activation, coercive fields in small systems exhibit a significant scatter. It is demonstrated that the statistics of coercive fields observed in molecular dynamics simulations is consistent with the statistical distribution expected for field-assisted thermally activated nucleation of reverse polarization domains. The excellent quantitative agreement between the simulation data and the theory of thermally activated processes provides strong evidence that polarization switching occurs by nucleation-and-growth rather than loss of the local minimum of the Gibbs free energy function. In a pristine crystal, switching is controlled by the field at which thermal fluctuations can create a critical nucleus in the bulk (homogeneous nucleation). The analysis of crystals with various vacancy-type defects demonstrates that such defects may enable heterogeneous nucleation at reduced fields. In both cases, the statistical analysis gives access to the respective activation energies, their field dependence, and the sizes of the critical nuclei. [ABSTRACT FROM AUTHOR]