Proton defects in BaTiO3: New aspects regarding the re-oxidation of dielectric materials fired in reducing atmospheres

The insulation resistance (IR) and the electrical endurance of Y-acceptor doped (Ba,Ca)(Ti,Zr)O3 ceramics, fired in reducing atmospheres, are significantly improved by a re-oxidation treatment. This effect has been studied by means of impedance spectroscopy (IS). Insulating grain boundary barrier layers were detected also without interaction with Ni-inner electrodes, as they are applied in multilayer ceramic capacitors (MLCCs). In moist firing atmospheres H2O vapor was found to react with oxygen vacancies, forming positively charged hydroxyl defects (OH)O
- on regular oxygen sites in the crystal lattice. Hopping of protonic defects is supposed to raise the ionic conductivity. Re-oxidation in dry gas mixtures of O2 and N2, however, desorbs water from the dielectric material and improves the IR. DC-field stress heavily degrades the grain boundary barriers. Protons in the dielectric material largely accelerate the electrical degradation. Hydroxyl defects are also considered to be responsible for alterations of the dielectric temperature characteristics at the Curie point.