STRUCTURE DETERMINATION AND SILVER ION CONDUCTIVITY OF LAYERED PEROVSKITE COMPOUNDS M2LA2TI3O10 (M=K AND AG)

A layered perovskite compound, Ag2La2Ti3O10, was newly synthesized by an ion exchange reaction of K2La2Ti3O10 with AgNO3 molten salt. The crystal structures of parent compounds K2La2Ti3O10.xH2O (x=0,2) and Ag2La2Ti3O10 were determined by Rietveld analysis. All of the structures were analogous to that of Ruddlesden-Popper phase with a tetragonal crystal system. Although the anhydrous K2La2Ti3O10 and Ag2La2Ti3O10 had almost the same crystal structure, a drastic difference in the bond character of M-O (M=K, Ag) was observed between the two compounds, i.e., completely ionic character for the K-O bond and relatively strong covalent character for the Ag-O bond along the direction of c axis. Such a covalent bond character in Ag2La2Ti3O10 was reflected to the conductivity behavior. An almost pure ion conduction of silver was observed at the temperatures below 200-degrees-C, while the mixed conduction with silver ion tranport number of 0.5 was observed over this temperature.