Molecular dynamics study of domain switching dynamics in KNbO3 and BaTiO3

In this work, we use molecular dynamics (MD) simulations to investigate factors affecting polarization switching dynamics in the single domain and 180 degrees bidomain models of BaTiO3 (BTO) and KNbO3 (KNO). In a single domain study for both materials, we observed that the hysteresis loop, while present in low-temperature phases, is essentially non-existent in the highest temperature non-cubic phase. We attribute this behavior to large spontaneous local polarization fluctuations leading to the effective elimination of the nucleation barrier that we observe. Interestingly, in the case of the bidomain structure, while we observe domain migration driven by the electric field, new domain nucleation is severely suppressed at high fields compared with single domain simulations. This behavior is explained by the suppression of simulation cell fluctuations due to the presence of the two domains. We give further credence to this conjecture by demonstrating that the artificial suppression of simulation cell dimension fluctuations in the case of a single domain switching also suppresses new domain nucleation. In this context, we discuss the role of size effects on polarization switching and phase changes in MD simulations.