Highly concentrated solvothermal synthesis of sub-10-nm BaTiO3 nanoparticles for optical applications

Single-crystalline barium titanate: BaTiO3 (BT) nanoparticles (NPs) with sub-10-nm size have been successfully obtained by a highly concentrated solvothermal synthesis using a high concentration of Ba(OH)2 and a titanium complex. To obtain sub-10-nm NPs, we focused on the gradual increase in the OH– ion concentration and the decrease in the dielectric constant of solvents, and BT NPs were produced in 1 h even at a low temperature of 200 °C. High-resolution transmission electron microscopy (HR-TEM) observation revealed that the resulting BT NPs were single-nanometer size, consisting of a single-crystalline structure. 1H-nuclear magnetic resonance (NMR) relaxation time (T2) and zeta potential measurements demonstrated that our BT NPs had high dispersibility and dispersion stability under acidic conditions. The yellowness index measurements revealed that the BT NPs dispersions exhibited colorless property. The resulting single nanometer-sized BT NPs are promising as high refractive index materials for optical applications due to being dispersed in optical resins.