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 an d the point defects disappear in the temperature range of 100 degrees -600 degreesC. Metal and oxygen vacancies combine to small nanometer-sized intra granular pores. At temperatures of >800 degreesC, the intragranular pores m igrate to the grain boundaries and disappear. In multilayer ceramic capacit ors that have been prepared from hydrothermal powders, the intragranular po res are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination.