X-RAY AND NA-23 NMR INVESTIGATIONS ON NA-BETA''-AL2O3 AND NA+()LA3+-BETA''-AL2O3 CRYSTALS/

The structure of a Na+/La3+-beta ''-Al2O3 crystal (degree of exchange xi = 80%) has been investigated by conventional single crystal X-ray d iffraction methods at room temperature. The lanthanide ions occupy eig htfold ccordinated mO (9d) as well as sevenfold coordinated BR sites ( 6c). Remaining Na+ ions were found exclusively in BR positions. Na-23 NMR measurements were performed at room temperature before and after t he exchange procedure. Two distinct Na-23 signals differing in angular dependence of the second order quadrupole resonance shifts were recor ded for the pure Na+-beta ''-Al2O3 crystal whereas in the case of the doped isomorph only one signal was detected. The Na-23 NMR signals wer e assigned to the two possible positions for the Na+ ions in the condu ction planes. (C) 1996 Academic Press, Inc.