Solid-state reaction mechanism for the formation of Ba6−xLn8+2 x/3Ti18O54 (Ln = Nd, Sm) solid solutions

A solid-state reaction mechanism for the formation of Ba6−xLn8+2x /3Ti18O54 (Ln = Nd, Sm) solid solutions has been studied using x-ray powder diffraction, thermal analyses, and transmission electron microscopy (TEM). During the interaction of the starting reagents, Ln2Ti2O7, BaTi4O9, and BaTiO3 are formed. In the next sequence, these three phases react together to form a high-x end member of the Ba6−xLn8+2x /3Ti18O54 homogeneity region (Ba3.9Nd9.4Ti18O54 and Ba3.9Sm9.4Ti18O54). Subsequently, the reaction of Ba3.9Nd9.4Ti18O54 and Ba3.9Sm9.4Ti18O54 with the residual BaTiO3 takes place. TEM investigations revealed that compositional inhomogeneities and structural defects existed in the Ba4Sm9.33Ti18O54 sample heated at 1370 °C for 1 h. Sintering times, prolonged to ≥3 h, eliminated the structural defects and increased the homogeneity of the sample.