To improve both the thermal stability and the electrical conductivity, alkali ion conducting carbonates and sulfates with admixtures of alkaline earth compounds as well as insulating materials such as γ-Al2O 3 were prepared and characterized by conductivity measurements, X-ray studies, DSC and SEM/EDX. The addition of the divalent carbonates and sulphates causes two effects. On the one hand side, the alkali earth compounds can be dissolved depending on the ionic radius to a more or less large extent, which is accompanied by an increase in the electrical conductivity. On the other hand side, a two phase mixture consisting of an excess of dopant is formed with an enhancement in the conductivity and improvement of the mechanical stability. This phenomenon, known as composite effect, could be observed in the following systems Na2CO3-BaCO3, Na2CO 3-SrCO3, Na2SO4-BaSO4, K2SO4-BaSO4, Na2SO 4-γ-Al2O3, K2SO 4-γ-Al2O3.