Crystal chemistry in the system MSbO3

Cubic, disordered phases of the compounds MSbO₃ (M = Li, Na, K, Rb, Tl, and Ag) have been investigated. KSbO₃ is readily synthesized in the disordered, cubic structure at high pressure, and the other isomorphic compounds were obtained by ion exchange. The structures of NaSbO₃ and AgSbO₃, which have space group Im3, were solved by X-ray single-crystal analysis. The structures contain an essentially rigid SbO₃ subarray consisting of pairs of edge-shared octahedra sharing common corners. Within this subarray, face-shared octahedra form 〈111〉 tunnels that intersect at the origin and body center of the unit cell, and the M⁺ ions are randomly distributed over two positions within these tunnels. Ordered, cubic phases have the primitive-cubic space group Pn3. The two M positions are different for Na⁺ and for Ag⁺ ions. At one of the Ag⁺-ion positions, the AgO bond length is only 2.26 Å, consistent with the gray-black color of AgSbO₃. Deformation of the 4d¹⁰ Ag⁺-ion core by 4d-5s hybridization appears to be induced by AgO covalent bonding. This conclusion is compatible with the observation that ion exchange is reversible for all compounds but AgSbO₃. Several properties of these compounds are compared with the super ionic conductors M₂O·11Al₂O₃ β-alumina.