EXAFS Study of Nanocrystalline Solid Solutions Synthesized in the ZrO₂-Ga₂O₃, System

Abstract
The local structure of (ZrO₂)_1-x(Ga₂O₃)_x/2 metastable solid solutions (x≤0.5) was investigated by EXAFS. These solid solutions crystallize in fluorite-like structures and are nanocrystalline. From the Ga K-edge spectra, the gallium atoms are found in an average fivefold coordination (d _Ga-O=1.89 Å). No signal corresponding to a second coordination shell is observed on the radial distribution functions. From the Zr K-edge spectra, a splitting of the Zr-O distances is evidenced. For the lowest gallium content (x≤0.14) the zirconium environment is of tetragonal type (4+4), whereas for the higher gallium content (cubic solid solutions) it is more or less similar to that found in monoclinic zirconia (3+4). The signal associated with the second shell decreases with increasing gallium content. These results indicate an important displacement of the gallium atoms in relation to their ideal position in a fluorite structure, which leads to a strong relaxation of the cation network.