Fabrication of Nanocrystalline BaTiO3 Ceramics by Ultra-High Pressure Sintering

10 nm raw BaTiO3 powder was sintered by ultra-high pressure assisted method at 6 GPa. The grain size of sintering samples is about 30 nm. The microstructures of sintering samples were studied by scanning electron microscope and atomic force microscopy. The results indicated that owing to the ultra-high pressure, the agglomerates in nano powders were broken down, and the densification was significantly increased. Additionally, the nucleation rate was increased due to reducing the energy barrier for nucleation and the growth rate was reduced due to the decrease of diffusivity. Thus, ultra-high pressure enables the specimen to be fabricated under relatively lower temperature and shorter period that assures to obtain dense nanocrystalline ceramics. The piezoelectricity was investigated by piezoelectric force microscopy. There existed some full piezoresponse hysteresis loops at different areas in 30 nm BaTiO3 ceramics, indicating the presence of piezoelectricity. In addition, oxygen vacancies were produced in strongly reducing atmosphere during ultra-high pressure sintering. F+ centers were formed because oxygen vacancies caught electrons, and therefore, the color of BaTiO3 ceramics became block.