Composite Structure of BaTiO₃Nanoparticle Investigated by SR X-Ray Diffraction

The size effects on the crystal structure and phase transitions have been investigated for BaTiO 3 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 BaTiO 3 fine particles consist of tetragonal and cubic structure components at 300 K. The structure model indicating that the cubic BaTiO 3 shell covers the tetragonal BaTiO 3 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.