High temperature 17O MAS NMR study scandia and yttria stabilized of calcia, magnesia, zirconia

High-resolution O-17 MAS NMR can provide unique constraints on local structure and oxide ion dynamics in conductive zirconia ceramics of interest for fuel cells and other technologies. We describe here NMR and bulk conductivity measurements for scandia, yuria, calcia, and magnesia stabilized zirconias, including MAS NMR spectra collected in situ at temperatures up to 700 degrees C. All of the cubic compounds with high dopant levels showed line narrowing and coalescence in this temperature range, and the temperature-induced changes in line widths are qualitatively correlated with the bulk conductivities. A monoclinic zirconia with 2% Sc2O3 dopant level (expected to have relatively low ionic mobility) showed no motional averaging of its two O-17 NMR peaks even at 600 degrees C, but instead is observed to begin to transform to a disordered, possibly cubic or tetragonal phase at 600 to 700 degrees C. O-17 MAS NMR spectra of calcia stabilized zirconia were analyzed in detail and the exchange frequencies as a function of temperature, conductivity, and activation energy were estimated and compared with bulk conductivities. The activation energy estimated from NMR exchange frequencies is somewhat lower than that of bulk conductivity but the conductivities estimated from NMR appear to be lower than bulk conductivity. (C) 2007 Elsevier B.V. All rights reserved.