X-ray-absorption spectroscopy of aNd3+-exchanged β’’-alumina crystal

We present an x-ray-absorption-spectroscopy study of the electronic and crystallographic structure around the ${\mathrm{Nd}}^{3+}$ ions in 60% Nd-exchanged sodium β’ ’-alumina crystal. Using a multishell best-fit analysis procedure, we reconstructed the ${\mathrm{Nd}}^{3+}$ 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 Å, while the Nd-Al(6c) is slightly increased by 0.13 Å. 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.