HREM studies of intergrowths in Sr2[Srn-1TinO3n+1] Ruddlesden-Popper phases synthesized by mechanochemical activation

A mechanochemical activation route has been applied in order to obtain the n= 1-4 and infinity members of the Sr-2[Srn-1TinP3n+1] Ruddlesden-Popper series from different (n+1)SrO:nTiO(2) Mixtures. The mechanosynthesis of SrTiO3 and Sr2TiO4 was observed during the milling process from the initial stoichiometric mixture, but in the cases of the n=2-4 members, a subsequent thermal treatment was needed. The synthesis protocol of Sr3Ti2O7 has been greatly improved and this compound can be isolated as a single, crystalline phase after annealing at 800 degrees C. In the case of Sr4Ti3O10 and Sr5Ti4O13, the formation temperature was also decreased, but members with n=3 and 4 could not be isolated. Detailed investigations using electron microscopy methods (TEM, HREM and SAED) were carried out in the samples corresponding to n = 2-4. Although a single ordered Sr3Ti2O7 structure is dominant in the sample corresponding to n = 2, a few intergrowths of other Ruddlesden-Popper phases were observed. In the cases of n=3 and 4, the intergrowths of Ruddlesden-Popper phases are more frequent than in the n=2 composition and are randomly distributed in the sample. The more frequent occurrence of such stacking faults, with increasing n value, leads to a somewhat disordered layer stacking sequence. (c) 2008 Elsevier B. V. All rights reserved.