Thermodynamically, the driving forc

Thermodynamically, the driving force for sintering is the reduction of the total interfacial energy of the system. Grain growth and densification are two factors which contribute to the decrease of the interfacial area. The grain growth is always determined by the intrinsic crystal growth of the ceramic and the influence of defects. Densification is mostly determined by the interface curvature of the adjacent particles in the green body. At sintering temperature, the BaTiO3 powders have a cubic phase.Using first principles, we calculated that the surface energy per unit area of {110} planes is ca 2.8 J/m2 while it is ca 1.0 J/m2 for {100} planes. It means that the preferred orientation is [110] direction, and growth along the [100] direction will be slow. As discussed above, the exposed planes of the obtained crystallites of the hydrothermal BaTiO3 are assigned to the {100} family. As a result, slow grain growth will occur during sintering. By contrast, particles prepared by hydrolysis method have a spherical shape whereby a variety of crystallographic planes are exposed.Then during the sintering, the grain growth will occur in all directions.