The effects of dopants on the electrical resistivity in lead magnesium niobate multilayer ceramic capacitors

Electrical resistivity studies were performed on multilayer ceramic capacitors (MLC) based on lead magnesium niobate and containing dopants of lead titanate, lead zinc niobate, and lead cobalt niobate. The results showed that lead titanate and/or lead zinc niobate had no effect on the electrical resistivity while lead cobalt niobate decreased the resistivity. In samples without lead cobalt niobate, the authors observed a conduction mechanism with an activation energy of ~1 eV, which is commonly observed in barium titanate based dielectrics. This is attributed to ionic conduction by the motion of oxygen vacancies. The increase in conductivity (or decrease in resistivity) resulting from the addition of lead cobalt niobate was attributed to electronic conduction through charge hopping among the cations. This conduction mechanism was characterized by an activation energy of ~0.5 eV. The transition between electronic and ionic conduction was a function of temperature and the concentration of lead cobalt niobate. Since the activation energy associated with the long-term failure was previously determined by a matrix of temperature and voltage accelerated-life tests to be ~1 eV, the authors conclude that conduction through charge hopping is not affecting the long-term reliability of these devices