Effect of synthesis conditions on the lithium nonstoichiometry and properties of La2/3-xLi3x□4/3-2xM2O6 (M = Nb, Ta) Perovskite-like solid solutions

The effects of the nominal composition and synthesis conditions on the lithium nonstoichiometry of La2/3 – xLi3x□4/3 – 2xNb2O6 (I) and La2/3 – xLi3x□4/3 – 2xTa2O6 (II) solid solutions are studied. The results demonstrate that lithium losses can be reduced from 26–30 to 14–15 mol % in system I and from 15 to 4 mol % in system II. It is shown that the disturbance of electroneutrality caused by Li nonstoichiometry in the solid solutions is eliminated via the formation of oxygen vacancies in positions O(1) (1f: 1/2 1/2 0) and O(2) (1h: 1/2 1/2 1/2) of the cation-deficient perovskite structure. The optimal lithium ion conductivity is offered by solid solutions with □/3x ≃ 2.6 and x ≃ 0.136–0.143.