Stabilization of Size-Controlled BaTiO3 Nanocubes via Precise Solvothermal Crystal Growth and Their Anomalous Surface Compositional Reconstruction

Crystal growth of barium titanate (BaTiO 3 ) using a wet chemical reaction was investigated at various temperatures. BaTiO 3 nanoparticles were obtained at an energy-efficient temperature of 80 °C. However, BaTiO 3 nanocubes with a preferred size and shape could be synthesized using a solvothermal method at 200 °C via a reaction involving titanium tetraisopropoxide [(CH 3 ) 2 CHO] 4 Ti for nucleation and fine titanium oxide (TiO 2 ) nanoparticles for crystal growth. The BaTiO 3 nanocubes showed a high degree of dispersion without the use of dispersants or surfactants. The morphology of BaTiO 3 was found to depend on the reaction medium. The size of the BaTiO 3 particles obtained using water as the reaction medium was the largest among the particles synthesized using various reaction media. In the case of alcohol reaction media, the BaTiO 3 particle size increased in the order methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol. Furthermore, BaTiO 3 powder obtained using alcohol reaction media resulted in cubic shapes as opposed to the round shapes obtained when water was used as the medium. We found that the optimal condition for the synthesis of BaTiO 3 nanocubes involved the use of 1-butanol as the reaction medium, resulting in an average particle size of 52 nm, which is the average distance of the cubes measured diagonally from corner to corner, and gives an average side length of 37 nm, and a tetragonal crystal system as evidenced by the powder X-ray diffraction pattern obtained using high-energy synchrotron X-rays. The origin of the spontaneous polarization of the BaTiO 3 tetragonal crystal structure was clarified by a pair distribution function analysis. In addition, surface reconstruction of BaTiO 3 nanocubes led to an outermost surface comprising two layers of Ti columns.