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

•Sub-10-nm BaTiO3 nanoparticles were solvothermally prepared in 1 h at 200 °C.•The size was controlled by controlling the OH– ion concentration and the dielectric constant.•The BaTiO3 nanoparticles show high dispersibility and dispersion stability under acidic conditions.•The BaTiO3 dispersions exhibited colorless property applicable for optical materials.