Dynamics of charge states at the surface of a ferroelectric nanoparticle in a liquid crystal

The liquid crystal with suspended ferroelectric nanoparticles is an interesting object for fundamental research on long-range dipole-dipole interactions. Additionally, it is promising for optical, optoelectronic and electrochemical applications. These suspensions can serve as basic elements for advanced nonvolatile memory cells and energy storage devices. The work studies cells filled with a nematic liquid crystal 5CB and cells containing 5CB with 0.5 and 1 wt.% of BaTiO3 nanoparticles with an average size of 24 nm. We analyzed the time dependences of the current flowing through the cells at a constant applied voltage and the voltage dynamics in the no-load mode. The time dependences of the current and voltage show a slowing-down decay rate. For the cells with BaTiO3 nanoparticles, the decrease in the time decay is characteristic. A possible physical reason for the retarding time decay is the indirect effect of screening charges, which cover ferroelectric nanoparticles, and slow ionic transport in the liquid crystal. To explain the dynamics of current and voltage, the finite element modeling of the polarization distribution, domain structure dynamics, and charge state of nanoparticles in a liquid crystal is performed using Landau–Ginzburg–Devonshire approach. Theoretical results confirmed the leading role of screening charges, because the surface of a ferroelectric nanoparticle adsorbs an ionic-electronic charge that partially screens its spontaneous polarization in single-domain and/or poly-domain states. When an electric field is applied to the liquid crystal with nanoparticles, it can release part of the screening charge (mainly due to the change in the polarization of the nanoparticle), which will lead to a decrease in the decay rate of the current and voltage dependences.