On the structural integrity of the spinel block in the β"-alumina structure.
The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.
Structure of the luminescent system Na+/UO2+β''‐alumina
The structure and ionic distribution of Na + β''-alumina with ∼12% of the sodium ions exchanged for the luminescent molecular uranyl ion (UO 2 2+ ) has been investigated at room temperature by single-crystal X-ray diffraction. The idealized formula for the crystal studied is (UO 2 ) y - Na 1+x-2y Mg x Al 11-x O 17 , with x=2/3 and y=0.10, M r =627.8
Temperature dependence of the Na+ distribution in Na+ β″-alumina
Abstract NMR techniques are used to show the existence of configurational changes occuring between 100 K and 200 K in Na β, Na-Li β and Na β″-alumina. When the static magnetic field is parallel to the c -axis, a peak appears, with decreasing temperature, on the low frequency side of the 23 Na central line. This peak is assigned to sodium ions belonging to ordered microdomains. In the Na-Li crystal below 100 K a line emerges in the high frequency portion of the spectrum which is related to the additional disorder induced by the substitution of Na + with Li + . The low frequency peak in Na β″ has spin-lattice relaxation rates smaller than the high frequency peak. This suggests that diffusional and short-range motions are hindered in the ordered microdomains.