Resistance variation in donor-doped PZT stacks with Cu inner electrodes under high field stress

Changes of the resistance of donor-doped lead zirconate titanate (PZT) under high voltages were investigated at temperatures from 350 to 500°C in different gas atmospheres. Measurements on individual ceramic layers (about 75 μm thickness) of PZT multilayer stacks with Cu inner electrodes allowed numerous experiments on nominally identical PZT material. Under high fields, the conductivity decreased significantly on time scales much longer than needed for capacitor charging. At 350°C, for example, decay times of several 1000 s were found. The time constant of this conductivity decay depends exponentially on temperature with activation energies of about 1.3 eV in air. After interrupting the field stress, thermally activated (ca. 1.1 eV) relaxation of the conductivity was found on an even longer time scale. The results are interpreted in terms of oxygen vacancy motion under high fields (stoichiometry polarization) and diffusive relaxation. The importance of oxygen migration despite donor doping is attributed to the high PbO volatility of PZT which readily leads to significant oxygen deficiency. Oxygen diffusion coefficients are estimated.