EXAFS DATA-ANALYSIS FOR LANTHANIDE SESQUIOXIDES

The EXAFS spectra of lanthanide sesquioxides (Lu2O3, Sm2O3, La2O3) at the lanthanide L(III)-edge are analysed. The complex coordination poly hedron around the lanthanide cation is modelled with the minimum numbe r of coordination shells that still allows the acquisition of coordina tion numbers and shell distances in agreement with the radial distribu tion functions from crystallographic data. Theoretical phase shifts an d backscattering amplitudes with an amplitude reduction factor, S-0(2) = 0.73, are reliable for reproducing the experimental EXAFS data. A m odel with one Lu-O and two Lu-Lu shells simulates the Lu coordination polyhedron in C-Lu2O3, while for La2O3 the model includes two oxygen s hells for simulating the nearest neighbours and one longer distance th at averages that of the La-La pairs. The coordination around Sm in Sm2 O3 is the most complex and two-shell models are needed to simulate the Sm-O and Sm-Sm absorber-backscatterer pairs. The models obtained are applied in the EXAFS analysis of dispersed Ln(2)O(3)/Al2O3 samples, wh ere X-ray diffraction fails to detect the structure adopted by the lan thanide phase. The results show that in an Sm2O3/Al2O3 sample calcined at 800 degrees C, very small Sm2O3 particles are formed. In an La2O3/ Al2O3 sample with low loading the analysis procedure allows the detect ion of the aluminium atoms that are present with the oxygens around th e lanthanum ions, thus suggesting the incipient formation of a bidimen sional LaAlO3 phase.