Size driven phase transition and thermodynamic properties of nanocrystalline batio3

Submicron powders of BaTiO3 with narrow size distribution were prepared by a modified sol-gel method. X-ray diffraction, Raman spectroscopy, calorimetry and Kurtz powder tests on nonlinear optical properties were applied to study size effects on ferroelectricity. The different methods show consistently that the ferroelectric properties disappear below a critical size of about 50 nm. The size driven phase transformation was found to be an order- to disorder transition similar to the well-known temperature driven transformation. From shifts of phase transformation temperatures with varying particle sizes, differences of surface free energies of different phases of BaTiO3, were calculated.