Quantitative ion exchange reactions to form Li2xVac2-2xLa2Ti3O9+x defect layered perovskites from H2La2Ti3O10 via solid acid/base reaction

Abstract

Layered and defect layered titanates are a wide class of ion exchangeable and technologically important ceramics. The majority of ion exchange methods employ excess reagents at elevated temperatures often leading to complete exchange. Control over the degree of ion exchange is desirable as this allows composition, structure and properties to be continuously tuned. Here, direct control over the degree of lithiation in the Ruddlesden-Popper n ​= ​3 derived phase H2La2Ti3O10, at room temperature using LiOH.H2O, is demonstrated. The resulting series H2-xLixLa2Ti3O10 (x ​= ​0, 0.125, 0.25, 0.5, 0.75, 1) can then be dehydrated allowing defect tuning in Li2xVac2-2xLa2Ti3O9+x defect layered perovskites. Materials containing a mixture of lithium cations and vacant sites often show fast-ion conducting but controlling the ratio has previously proved challenging. The synthesis and degree of exchange is investigated using X-ray powder diffraction data, thermogravimetric analysis and the ionic mobility assessed via a.c. impedance spectroscopy. As use of LiOH.H2O has now been shown to directly control ion exchange in both n ​= ​1 and n ​= ​3 phases the possibility of the methodology being applied more generally to layered materials is discussed.