Effect of doping ferroelectric BaTiO3 nanoparticles on dielectric, electro-optical, and ionic properties of antiferroelectric bent-core liquid crystal

Abstract

Nano-doping in polar bent-core liquid crystals is the topic of current interest for designing multifunctional smart materials. Here, we study the effect of doping of two different-sized (5–15 nm and 50–70 nm) ferroelectric BaTiO3 nanoparticles on the dielectric, electro-optical and ionic properties of antiferroelectric smectic A bent-core liquid crystal. Doping with both the sizes of nanoparticles results in lowering of the transition temperature of the liquid crystal mesophases. Both, the pure as well as doped samples show a soft mode in their antiferroelectric smectic A phase. In comparison to pure liquid crystal, the dielectric strength of the soft mode in doped samples is decreased, while their relaxation frequencies show an increasing behavior. Additionally, a decrement has been observed in the spontaneous polarization of the doped samples. A drop in polarization as well as soft mode dielectric strength values in doped samples, simultaneously point to an antiparallel dipole–dipole correlation between the ferroelectric nanoparticles and antiferroelectric liquid crystal molecules. Higher values of molecular mode relaxation frequencies obtained in nano-doped samples indicate a decrement in viscosity and dilution of pure liquid crystal. An important electro-optical parameter, the response time shows a remarkable decrement for the higher size (50–70 nm) nanoparticles doped sample. An enhancement in direct current conductivity and ion diffusion coefficient is observed for both the nano-doped samples. The smaller size (5–15 nm) ferroelectric nanoparticles reduce the mobile ion concentration and act as ion-capturing agents for the liquid crystal. A systematic investigation of the nano-doped bent-core liquid crystal can catalyze the use of the combined media for faster switching electro-optic applications.