Abstract
The local order around Zr and Y atoms of nanocrystalline yttria-stabilized zirconia (YSZ) powders with different grain sizes has been investigated by x-ray absorption spectroscopies. The samples were prepared by means of mechanical alloying with or without subsequent sintering treatment and also by milling commercial YSZ. Our study is motivated by the interest in the electrical properties of grain boundaries and the controversy about the level of disorder in the intergrain regions in nanocrystalline YSZ. The x-ray absorption near edge structure (XANES) analysis indicates that the local order of all the sintered samples is independent of the grain size. This is confirmed by the analysis of the extended x-ray absorption fine structure, which points out also that, in contrast to that found in sintered samples, the local order around the cation in the samples milled without further sintering treatment extends only to the first coordination shell. Finally, the results of ab initio Zr K-edge XANES calculations lead us to conclude that the observed changes of the shape of the white line are not related to a phase transformation but reflects the short-range order present in the as-milled samples.
Highlights
Yttria-stabilized zirconia [yttria-stabilized zirconia (YSZ): (Y2O3)x(ZrO2)1−x] is a well known oxygen ion conductor
This is confirmed by the analysis of the extended x-ray absorption fine structure, which points out that, in contrast to that found in sintered samples, the local order around the cation in the samples milled without further sintering treatment extends only to the first coordination shell
Several x-ray absorption spectroscopy (XAS) studies have been reported to date for solid ZrO2-Y2O3 solutions or nanocrystalline YSZ materials for which the structural disorder plays an important role
Summary
Yttria-stabilized zirconia [YSZ: (Y2O3)x(ZrO2)1−x] is a well known oxygen ion conductor. Doping with Y2O3 stabilizes the cubic fluorite structure of ZrO2 and supplies the oxygen vacancies responsible for the ionic conduction.. Long-range transport of oxygen ions occurs by thermally activated hopping to adjacent oxygen vacancies, resulting in a dc conductivity, which follows an Arrhenius law. By means of chemical substitution the operating temperature of oxide-ion conductors has been reduced to the range of 700◦ C,2,3 but this temperature is still too high for many technological applications. The effect of the dimensionality has been related with the ionic transport and, recently, nanoionics has emerged as a promising path toward enhanced values of the ionic conductivity in nanostructured materials.. Interesting effects appear when the characteristic dimensions of the system become comparable to the extension of the space-charge regions at grain boundaries. The effect of the dimensionality has been related with the ionic transport and, recently, nanoionics has emerged as a promising path toward enhanced values of the ionic conductivity in nanostructured materials. interesting effects appear when the characteristic dimensions of the system become comparable to the extension of the space-charge regions at grain boundaries.
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