Theoretical and experimental study of the core structure and mobility of dislocations and their influence on the ferroelectric polarization in perovskite KNbO3

Potassium niobate KNbO3 is a lead-free perovskite and a promising candidate to replace lead-containing ferroelectrics related to PbTiO3. In this study, we use atomistic computer simulation and transmission electron microscopy to investigate dislocations in KNbO3, 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 ⟨110⟩{11¯0} 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 ⟨100⟩{010} 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.