Ionic and electronic conductivity in lead-zirconate-titanate (PZT)

Accurate impedance measurements on differently sized samples of lead–zirconate–titanate (PbZr0.53Ti0.47O3, PZT) have been analyzed with a CNLS procedure, resulting in the separation of the ionic and electronic conductivities over a temperature range from f150 to 630 jC. At 603 jC the electronic conductivity shows approximately a (PO2)1/4 dependence, while the ionic conductivity remains constant. Below the Curie transition temperature the oxygen non-stoichiometry becomes frozen-in and the conductivities are strongly dependent on the sample history with respect to temperature sequence and ambient PO2. A tentative interpretation assumes defect association, i.e. formation of neutral [VPb"–VO ]x complexes, and electron-hole transfer between lead sites and lead vacancies to control the oxygen ion conductivity in the tetragonal phase. Annealing PZT-based devices at about 600 jC under low oxygen pressure (_1 Pa oxygen) effectively decreases the low temperature electronic conductivity by a factor of 100 and the ionic conductivity by a factor of 10–15 with respect to normal air processing.