X-ray-absorption spectroscopy of-exchanged β-alumina crystal

The results of x-ray-absorption spectroscopy investigations of (Formula presented) ions in a nearly fully exchanged (93%) sodium β-alumina crystal are reported. The (Formula presented) local environment is reconstructed using a multishell best fit procedure and is compared with existing structural models. The experimental extended x-ray-absorption fine-structure (EXAFS) spectra are also compared with model ab initio FEFF6 calculations based on the x-ray-diffraction data for the (Formula presented) ions located at the BR(2d) and interstitial A(6h) sites of β-alumina. Neodymium ions are mainly found near the BR(2d) sites of the conduction plane, where they are strongly bonded to three O(5) oxygens located in the same plane and shifted by ∼0.6 Å from the crystallographic positions occupied in sodium β-alumina. The atoms located at the spinel blocks below and above the conduction plane produce negligible contribution to the total Nd (Formula presented) edge EXAFS signal due to the polarization effect and, mainly, to thermal and/or static disorder. The similarity of the local structure around the (Formula presented) ions in the β- and (Formula presented)-alumina crystals is also discussed.