Enhanced specific grain boundary conductivity in nanocrystalline Y2O3-stabilized zirconia

Stabilized zirconia samples containing 1.7 and 2.9 mol% Y2O3 with average g rain sizes of 25-50 nm were prepared by pressureless sintering and hot-pres sing. Phase content, microstructure and average grain size of the samples w ere examined using X-Ray Diffraction (XRD) and High Resolution Scanning Ele ctron 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 de ionic conductivities of the grain interior (bulk) and of the grain boundar ies. The activation energies of both processes were slightly lower as for c omparable microcrystalline samples as reported in the literature. This resu lt is attributed to the complete tetragonal structure and the low Si-conten t of the samples. The conductivities of the bulk and the grain boundary pro cess 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-cont ent and its grain size-dependent segregation in the nanocrystalline samples . (C) 1999 Elsevier Science B.V. All rights reserved.