Oxygen Ion Conduction in Bulk and Grain Boundaries of Nominally Donor-Doped Lead Zirconate Titanate (PZT): A Combined Impedance and Tracer Diffusion Study

Oxygen ion conduction in Nd3+-doped Pb(ZrxTi1-x)O-3 (PZT) was investigated by impedance spectroscopy and O-18-tracer diffusion with subsequent secondary ion mass spectrometry (SIMS) analysis. Ion blocking electrodes lead to a second relaxation feature in impedance spectra at temperatures above 600 degrees C. This allowed analysis of ionic and electronic partial conductivities. Between 600 degrees C and 700 degrees C those are in the same order of magnitude (10(-5)-10(-4)S/cm) though very differently activated (2.4eV vs. 1.2eV for ions and electron holes, respectively). Oxygen tracer experiments showed that ion transport mainly takes place along grain boundaries with partly very high local ionic conductivities. Numerical analysis of the tracer profiles, including a near-surface space charge zone, revealed bulk and grain-boundary diffusion coefficients. Calculation of an effective ionic conductivity from these diffusion coefficients showed good agreement with conductivity values determined from impedance measurements. Based on these data oxygen vacancy concentrations in grain boundary and bulk could be estimated. Annealing at high temperatures caused a decrease in the grain-boundary ionic conductivity and onset of additional defect chemical processes near the surface, most probably due to cation diffusion.