Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3

Oxygen vacancy kinetics in ferroelectric PbZr0.4Ti0.6O3 were studied by (18)oxygen (O-18) tracer self-diffusion in epitaxial thin films as well as bulk polycrystalline samples. O-18 exchange annealing was carried out at an oxygen partial pressure of 250 mbar and temperatures between 250 and 400 degrees C. Isotope depth profiling was performed by secondary ion mass spectrometry as well as neutral secondary mass spectrometry. The observed concentration depth profiles of the polycrystalline samples show two distinct diffusion paths, namely, bulk diffusion and grain boundary (GB) diffusion. It appears to be of type B-kinetics in the investigated temperature range, with D-GB/D-bulk >> 100. Donor doped samples with different levels of Nb5+ (1-4 mol. %) were also investigated. The effect on the diffusion depth profiles, however, were negligible and can solely be attributed due to the change in the samples microstructure as induced by the dopants. A diffusion coefficient for the bulk diffusion of the O-18 isotope, D-bulk = 10 +/- 5 x 10(-8) cm(2)/s exp(-0.87 +/- 0.1 eV/kT) was found. The faster GB diffusion process shows an activation enthalpy of only E-A=0.66 +/- 0.2 eV. (c) 2008 American Institute of Physics.