On the structure type of Na10MgTi10O26

The analysis of the Weissenberg photographs from the solid electrolyte of t he composition Na8+xMgx/2Ti11-x/2O26 showed that the superstructural reflec tions and the apparent change of the symmetry from monoclinic to orthorhomb ic are caused by twinning with the specific ratio of its unit-cell paramete rs, b/4a approximate to cos gamma. The analysis of the interatomic distance s and bond valences allowed the refinement of the compound composition (x a pproximate to 1.5) and the establishment of a position occupied mainly by m agnesium. The X-ray phase analysis of quaternary oxide systems has showed t hat the structure type under question can be stabilized not only by Mg2+, Z n2+, and Sc3+ ions, but also by a manganese ion, Mn2+, however, it cannot b e 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 an almost complete substitution of these ions by silver io ns occurring during ion exchange, by their substitution by lithium, and sod ium extraction during Mn2+ oxidation. The oxygen coordination and rather ra re occurrence of the structure type under question are discussed.