Defect chemistry and microstructure of hydrothermal barium titanate

Hydrothermal powders of BaTiO3 and (Ba,Ca)(Ti,Zr)O-3 contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100 degrees -600 degreesC. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800 degreesC, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination.