Effect of nano-grain size on the ionic conductivity of spark plasma sintered 8YSZ electrolyte

Densification and micro-structural development of ultra fine 8 mol% yttria stabilized zirconia (8YSZ) nano powder were investigated systematically by varying the SPS sintering temperature at constant applied pressure of 50 MPa. A hundred fold decrease in average grain size ranging from 10 gm to 80 nm is observed on decreasing the SPS sintering temperature from 1200 degrees C to 1050 degrees C with > 99% of theoretical densities. Impedance measurements on the samples indicated an enhancement in the ionic conductivity at 700 degrees C from 0.004 S/cm to 0.018 S/cm with decrease in grain size from 10 mu m to 0.51 mu m and a significant increase in conductivity from 0.018 S/cm to 0.068 S/cm on further reduction of grain size to 80 nm. A significant change in the grain-boundary conductivity is noticed on reducing the grain sizes to nano regime. The diverse microstructure with ultra fine grain size resulting from SPS at 1050 C could contribute to the enhanced ionic conductivity, which is supported by the activation energy data. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.