Fast re-oxidation kinetics and conduction pathway in Spark Plasma Sintered ferroelectric ceramics

The re-oxidation kinetics of BaTiO3 ceramics sintered by Spark Plasma Sintering (SPS) was investigated using in situ impedance spectroscopy. Thanks to the flexibility of the SPS process, the grain size of the dense ceramics was tuned from 0.5 pm to 10 mu m. The re-oxidation kinetics are found to be very fast regardless of the grain size and a full re-oxidation of the ceramics are achieved after 20 h of exposure to an ambient environment at only 600 degrees C. The residual density of charge carriers is reduced when using finer starting powders. SPS ceramics made with micrometer size grains demonstrate a residual charge-carrier density that is one tenth that of ceramics made from 10 mu m particles. Grain-boundary conduction is dominant through fine-grain SPS ceramics. This latter feature is similar to BaTiO3 sintered using the conventional route with 10 mu m size grain. Finally, the critical grain size for optimal dielectric permittivity is found to shift from 0.7 mu m in standard ceramics to 1.5 mu m in SPS ceramics.