Short- and long-range order in Na(I)-Eu(II) β double-prime-alumina

When the Na(I) content of the two-dimensional fast ionic conductor Na(I) β double-prime-alumina is partially or fully replaced with Eu(II), the mobile cations in the resulting isomorphous materials have varying degrees of short- and long-range order. Single-crystal x-ray structure refinements of four such compositions are reported here. These results, as well as data from TEM and optical spectroscopy studies, can be interpreted in terms of a model in which the mobile ion distribution in the materials is determined by mobile ion-framework interactions, mobile ion-mobile ion interactions, and kinetic effects related to the thermal history of the samples