**3. Results and Discussion**

The TiO2-seeded growth process of BaTiO3 nanocrystals is shown in Figure 1. The commercially available TiO2 (P25) nanoparticles, with a mixed phase of anatase and rutile and a size range of 20–25 nm, are used as the Ti source and seeds in the synthesis of BaTiO3 nanocrystals via a conventional hydrothermal process in a strongly basic aqueous solution. In this synthesis, TiO2 nanoparticles can first react with NaOH and form insoluble titanate species (e.g., Na2TiO3), which then act like the crystal nucleus to form BaTiO3 nanocrystals by reacting with Ba2<sup>+</sup> ions under the hydrothermal conditions. We systematically investigated the effects of molar ratios of Ba/Ti (*R*Ba/Ti), hydrothermal temperature (*T*/ ◦C) and time (*t*/h) on the phase, morphology and particle size of the BaTiO3 nanocrystals.
