Oxygen Nonstoichiometry in Sr₄Fe₆O_13-δ:  The Derivatives [Sr₈Fe₁₂O₂₆]·[Sr₂Fe₃O₆]_n

Abstract

Different samples of the ferrite “Sr4Fe6O13”, synthesized in air, nitrogen, and argon, have been studied by high-resolution electron microscopy. It is shown that this oxide is oxygen-deficient, i.e., Sr4Fe6O13 - δ, and that its structure is modulated. The electron diffraction study shows that the modulation vector is p a⃗* + q c⃗*, with p = (1 − δ)/2 varying in the range [0.4−0.5] and q close to 1. It is shown that the component of the modulation vector along c⃗ induces complex modulated structures. It is also demonstrated that oxygen nonstoichiometry corresponds to the generation of microphases [Sr8Fe12O26] [Sr2Fe3O6] n , whose first integral member n = 1, which corresponds to p = 0.4, is isolated here for the first time by synthesis under argon. Structural models involving intergrowths of single perovskite [Sr2Fe2O6]∞ layers with complex [Sr2Fe4O7 - δ]∞ layers involving two kinds of pyramidal ribbons, FeO5 trigonal bi-pyramids and FeO5 distorted tetragonal pyramids, explain the oxygen deficiency.

Thickness-dependent transport properties of Sr4Fe6O13 epitaxial thin films

“…One of the most interesting points has to do with the intriguing oxygen superstructure modulation observed both in thin films [12] and in ceramic samples [27,28] that could affect the carrier concentration and so the transport properties.…”

Unusual Strain Accommodation and Conductivity Enhancement by Structure Modulation Variations in Sr4Fe6O12+δ Epitaxial Films

“…[8,9] The aniondeficient Sr 4 Fe 6 O 12þd (d < 1) derivatives present, in comparison with the stoichiometric Sr 4 Fe 6 O 13 phase, a very similar layered structure but with lower oxygen content in…”

Reinvestigation of the Fe-rich part of the pseudo-binary system SrO–Fe2O3

“…[8]). It's precise crystal structure description lead to the detection of structural incommensurability [9].…”