Solid-state reaction mechanism for the formation of Ba(6-x)Ln(8+2) x/3Ti18O54 (Ln = Nd, Sm) solid solutions

A solid-state reaction mechanism for the formation of Ba(6-x)Ln(8+2x/3)Ti(1 8)O(54) (Ln = Nd, Sm) solid solutions has been studied using x-ray powder d iffraction, thermal analyses, and transmission electron microscopy (TEM). D uring the interaction of the starting reagents, Ln(2)Ti(2)O(7), BaTi4O9, an d BaTiO3 are formed. In the next sequence, these three phases react togethe r to form a high-x end member of the Ba(6-x)Ln(8+2x/3)Ti(18)O(54) homogenei ty region (Ba3.9Nd9.4Ti18O54 and Ba3.9Sm9.4Ti18O54). Subsequently, the reac tion of Ba3.9Nd9.4Ti18O54 and Ba3.9SM9.33Ti18O54 with the residual BaTiO3 t akes place. TEM investigations revealed that compositional inhomogeneities and structural defects existed in the Ba4SM9.33Ti18O54 sample heated at 137 0 degreesC for 1 h. Sintering times, prolonged to greater than or equal to3 h, eliminated the structural defects and increased the homogeneity of them sample.