Stabilization of the n=3 Ruddlesden-Popper phases:: Sr4Mn3-xFexO10-δ and Sr4-yCayMn3O10-δ

Sr4Mn3O10, which crystallizes in space group Cmca, is not a Ruddlesden-Popper (RP) phase. The partial substitution of either Mn by Fe or Sr by Ca leads to a stable n = 3 RP phase with tetragonal symmetry (I4/mmm). The minimum amount of Fe or Ca needed to obtain a stable RP phase is x = 0.40 for Sr4Mn3-xFexO10-delta and y = 2.85 for Sr4-yCayMn3O10-delta. High-resolution transmission electron microscopy and selected area electron diffraction electron microscopy indicate that about 50% of the grains have well-ordered n = 3 structure for both series of RP phases, while the rest of the grains show significant intergrowth between the n = 2 and n = 3 structures. Sr4Mn2.6Fe0.4O10-delta and Sr1.15Ca2.85Mn3O10-delta are semiconductors and exhibit spin-glass like transitions at low temperature.