Enhanced specific grain boundary conductivity in nanocrystalline Y 2O 3-stabilized zirconia

Abstract

Stabilized zirconia samples containing 1.7 and 2.9 mol% Y 2O 3 with average grain sizes of 25–50 nm were prepared by pressureless sintering and hot-pressing. Phase content, microstructure and average grain size of the samples were examined using X-Ray Diffraction (XRD) and High Resolution Scanning Electron Microscopy (HRSEM). The density of the samples measured based on the Archimedes Principle was in the range of 93–96% of the theoretical density. The samples were also investigated using X-ray Photoelectron Spectroscopy (XPS) for traces of Si. Impedance Spectroscopy was used to determine the dc ionic conductivities of the grain interior (bulk) and of the grain boundaries. The activation energies of both processes were slightly lower as for comparable microcrystalline samples as reported in the literature. This result is attributed to the complete tetragonal structure and the low Si-content of the samples. The conductivities of the bulk and the grain boundary process were in the same range as for microcrystalline samples. Therefore, due to the much smaller grain size the specific grain boundary conductivities of the nanocrystalline samples is 1–2 orders of magnitude higher than that of the microcrystalline samples. This is also attributed to the low Si-content and its grain size-dependent segregation in the nanocrystalline samples.