Structural determinations of single-crystal K β-alumina and cobalt-doped K β-alumina

Single-crystal structural refinements of K β-alumina and Co ²⁺-doped K β-alumina show that the distribution of potassium ions in the diffusing planes is very similar to that in the isomorphous compound Na β-alumina but quite different from Ag β-alumina. The Co ²⁺ ions selectively fill the underbonded, tetrahedrally coordinated, Al(2) sites in the middle of the spinel block portion of the structure. This tends to support the aluminum vacancy mechanism of charge compensation. The positional parameters of the spinel block are well-determined and appear insensitive to the diffusing plane ions and arrangement.