Oxide Ion Transport in Donor‐Doped Pb ( Zr _x Ti _{1− x} ) O ₃ : Near‐Surface Diffusion Properties

Abstract

Oxide ion transport in Pb ( Zr x Ti 1– x ) O 3 ( PZT ) was investigated using 18 O tracer diffusion and time‐of‐flight secondary ion mass spectrometry analysis. Particularly diffusion in the near‐surface regions (a few 100 nm in depth) is discussed and strong evidence for a space charge layer near the surface is provided. In this layer, an enrichment of oxygen vacancies is found at temperatures up to 600°C, resulting in box‐shaped tracer diffusion profiles. At 650°C, however, the profile shape is modified and reveals a depletion of oxygen vacancies close to the surface. Accordingly, a change in the polarity of the surface charge takes place between 600°C and 650°C. The tracer diffusion profiles are very sensitive to surface modification, caused by etching or annealing at higher temperature, and also depend on the sintering procedure. Moreover, application of an external field during the tracer experiments affected the tracer diffusion at the cathode, while leaving the profile at the anode unperturbed. Quantitative analysis of the profiles was performed by means of numerical calculations based on Gouy‐Chapman or Mott‐Schottky space charge models. Estimates of the oxygen vacancy concentration and ionic transference number of donor‐doped PZT are provided.