On the structure type of Na10MgTi10O26

The analysis of the Weissenberg photographs from the solid electrolyte of the composition Na8+xMgx/2Ti11-x/2O26 showed that the superstructural reflections and the apparent change of the symmetry from monoclinic to orthorhombic are caused by twinning with the specific ratio of its unit-cell parameters, b/4a≅cos γ. The analysis of the interatomic distances and bond valences allowed the refinement of the compound composition (x≅1.5) and the establishment of a position occupied mainly by magnesium. The X-ray phase analysis of quaternary oxide systems has showed that the structure type under question can be stabilized not only by Mg2+, Zn2+, and Sc3+ ions, but also by a manganese ion, Mn2+, but cannot be stabilized by smaller (Ti3+,V3+...Ni2+) cations. The mobility of all the sodium ions (even those located in the narrowest tunnels of the structure) is confirmed by almost complete substitution of these ions by silver ions occurring during ion exchange, by their substitution by lithium, and sodium extraction during Mn2+ oxidation. The oxygen coordination and rather rare occurrence of the structure type under question are discussed