Composite structure of BaTiO3 nanoparticle investigated by SR X-ray diffraction

The size effects on the crystal structure and phase transitions have been investigated for BaTiO3 fine particles of 700, 400, 300 and 100 nm size, by means of powder diffraction using synchrotron radiation (SR) high-energy X-rays. The Rietveld refinement reveals that the BaTiO3 fine particles consist of tetragonal and cubic structure components at 300 K. The structure model indicating that the Cubic BaTiO3 shell covers the tetragonal BaTiO3 core is examined. The thickness of the cubic shell is estimated at approximately 8 nm, which is almost constant irrespective of particle sizes, and the Volume ratio of the cubic component increases with decreasing the particle size. Successive phase transitions are detected even in 100 nm size particles, where only the tetragonal component undergoes the phase transition.