X-ray-absorption spectroscopy of a Nd3+-exchanged β-alumina crystal

We present an x-ray-absorption-spectroscopy study of the electronic and crystallographic structure around the Nd3+ ions in 60% Nd-exchanged sodium β''-alumina crystal. Using a multishell best-fit analysis procedure, we reconstructed the Nd3+ local environment and compared it with existing structural models. We found that neodymium ions are mainly located near the mO(9d) sites of the conduction region; they are strongly bonded to two O(5) oxygens which are located in the same plane and shifted from their ideal crystallographic positions in sodium β'' alumina crystal. In particular, with respect to crystallographic parameters of sodium β'' alumina, the Nd-O(5) distance is shortened by 0.36 , while the Nd-Al(6c) is slightly increased by 0.13. Comparative analysis of Debye-Waller factors obtained for different coordination shells shows evidence of correlation in the vibrational motion of neodymium with the O(5) oxygens and with the Al(6c) aluminums.