Abstract
The series of complex aluminates RE 2SrAl 2O 7 (RE = La, Nd, Sm, Eu, Gd, Tb, Dy, Ho) was prepared at 1450 °C. Their structure is the double perovskite slab–rocksalt layer P 2/RS intergrowth of the n=2 Ruddelsden–Popper phases. X-ray Rietveld refinement calculations point to a progressive RE-Sr ordering between the ninefold sites in the RS layers and the twelvefold one in the P 2 slabs, respectively. This ordering proves both to improve the ease to prepare these aluminates and stabilize their intergrowth structure. The limit observed for RE=Ho corresponds to a nearly fully ordered distribution of the Ho 3+ and Sr 2+ cations – 91%. Due to an excess structure-bonding anisotropy in the ninefold sites, a further extent to smaller RE 3+ cations is unsuccessful. These results well compare with those regarding the magnetoresistant manganites RE 1+ x Sr 2− x Mn 2O 7: increasing RE-Sr ordering and limit found for Er. The big size A element long range ordering phenomena which are unlikely to depend on redox phenomena of the B element in the P 2 slabs, have to be considered as specific trends of the P 2/RS intergrowth type complex oxides.
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