We examined the influence of nanocrystalline particle size on the cubic-to-tetragonal phase transition of barium titanate (BaTiO3). In-situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used in combination with electron microscopy to study the evolution of lattice structure and phase-transformation behavior with heat treatment and particle growth for BaTiO3. The lattice constants were obtained for various polycrystal orientations in the diameter size range 10-90 nm. In-situ XRD results during the crystallization of amorphous 4BaTiO(3)-SiO2 revealed a critical size of similar to 25 nm for the cubic-to-tetragonal phase transition of BaTiO3 at room temperature. (C) 2009 Elsevier B.V. All rights reserved.