Potassium niobate ${\mathrm{KNbO}}_3$ is a lead-free perovskite and a promising candidate to replace lead-containing ferroelectrics related to ${\mathrm{PbTiO}}_3$. In this study, we use atomistic computer simulation and transmission electron microscopy to investigate dislocations in ${\mathrm{KNbO}}_3$, first to establish the relationship between their atomic-scale properties and the macroscopic mechanical behavior, and second to study their influence on the ferroelectric properties of the material. The easiest dislocation glide system is found to be $\langle 110\rangle \left\{1\overline{1}0\right\}$ at all temperatures, independent from structural phase transformations. The mobility of dislocations and the evolution of the microstructure are measured from room temperature up to 1173 K. A sharp transition in the yield stress is found around 800 K, attributed to the additional activation of the $\langle 100\rangle \left\{010\right\}$ glide system at high temperature. Atomistic simulations quantify the effect of dislocations on the ferroelectric polarization, and TEM observations give indication of the nucleation of domain walls at dislocation cores.

• Received 17 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.214101