Pressure-Induced Phase Transition in BaTiO₃ Nanocrystals

The crystal structure and electric properties of BaTiO₃ nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO₃ nanocrystals that are tetragonal phase with grain sizes more than 100nm, but also in the samples of BaTiO₃ nanocrystals that are cubic phase with grain sizes less than 100nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10GPa for crystallites ranging from 200 to 10nm in radius. The bulk moduli are calculated according to Birch--Murnaghan state equation before and after the phase transition.