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Barium titanate (BaTiO_3) and strontium titanate (SrTiO_3) nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO_2 particles and corresponding alkaline earth hydroxides, Ba(OH)_2 and Sr(OH)_2 respectively, in 50 mol·dm~(-3) KOH solution at 150℃. Each structural evolution of BaTiO_3 and SrTiO_3during the hydrothermal treatment was investigated by X-ray diffraction (XRD), field emission scanning elec-tron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM) and thermogravimetry-differential analysis (TG-DTA). In the BaTiO_3 system, round particles with cubic perovskite-type structure were obtained within 1h. However, these particles were gradually dissolved and then were re-precipitated in the form of cube-shape BaTiO_3 particles with a smaller lattice constant a_c than that of the former phase. After the BaTiO_3 particles formed firstly have disappeared completely, or the two phases coexistence stage with different lattice constant a_c passed, lattice constant a_c of BaTiO_3 phase re-precipitated continuously decreased with annealing time. In contrast, once SrTiO_3 particles are formed, the lattice constant a_c decreased continuously throughout the reaction. The result indicates that SrTiO_3 particles were annealed without dissolution and precipitation process under the present condition.

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