Structural Ordering Supremacy on the Oxygen Reduction Reaction of Layered Iron-Perovskites

Abstract

Layered perovskites of the Gd0.8–x Ba0.8Ca0.4+x Fe2O5+δ system show oxygen reduction reaction (ORR) activity. The layered crystal structure of these oxides is established by the interplay of the Gd3+, Ba2+, and Ca2+ locations with the ordering of the coordination polyhedra of the Fe3+ cations. Substitution of Gd3+ by Ca2+ increases the oxygen deficiency that is accommodated by the formation of layers of FeO5-squared pyramids intercalated with A–O layers containing mainly Gd3+. The presence of FeO5-squared pyramids in the crystal structure promotes the oxygen diffusion and then the ORR activity. Therefore, GdBa2Ca2Fe5O13 is the oxide of the system which presents lower area specific resistance (ASR) values when it is applied as an electrode in symmetrical cells using Ce0.9Gd0.1O2−δ as an electrolyte.

3D to 2D Magnetic Ordering of Fe3+ Oxides Induced by Their Layered Perovskite Structure

“…Figure S2 displays the representation of the building blocks of the crystal structures of the three compounds. Analogous to the previously reported structure of Gd compounds, 17 , 18 these crystal structures consist of layered ordering of the RE 3+ , Ba 2+ , and Ca 2+ cations in combination with layered ordering of the different coordination polyhedra of the Fe atoms along the stacking c -axis. Substitution of RE by Ca in the systems modifies the layered ordering of these cations and the oxygen content in such a way that the RE 3+ , Ba 2+ , and Ca 2+ ordering is established in blocks of 3 a p periodicity in the RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 oxides; in blocks of 5 a p periodicity in the REBa 2 Ca 2 Fe 5 O 13 oxides; and by intercalation of blocks of 3 a p and 5 a p periodicity in the intermediate RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 compounds.…”

“…Substitution of RE by Ca in the systems modifies the layered ordering of these cations and the oxygen content in such a way that the RE 3+ , Ba 2+ , and Ca 2+ ordering is established in blocks of 3 a p periodicity in the RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 oxides; in blocks of 5 a p periodicity in the REBa 2 Ca 2 Fe 5 O 13 oxides; and by intercalation of blocks of 3 a p and 5 a p periodicity in the intermediate RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 compounds. 17 , 18 The different RE 3+ , Ba 2+ , and Ca 2+ ordering drives the formation of the different Fe-coordination polyhedra (tetrahedron, octahedron, and square pyramid) and their different layered ordering leading to the current structures. 17 , 18 …”

“… 17 , 18 The different RE 3+ , Ba 2+ , and Ca 2+ ordering drives the formation of the different Fe-coordination polyhedra (tetrahedron, octahedron, and square pyramid) and their different layered ordering leading to the current structures. 17 , 18 …”

“…EELS analysis also agrees with Fe 3+ . 17 , 18 Figure 1 shows the Mössbauer spectra of Gd 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 and GdBa 2 Ca 2 Fe 5 O 13 collected at room temperature and Table 1 summarizes the corresponding IS, QS, and HF parameters. The spectrum of GdBa 2 Ca 2 Fe 5 O 13 consists of three different components in an area ratio of 1:2:2; two of them with IS and QS values attributed to Fe 3+ sites in octahedral and tetrahedral coordination like in G 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 17 and a third component with IS and QS values of 0.39 and −0.53 mm/s, respectively, associated with Fe 3+ in the square pyramidal environment.…”

“…We have studied the influence of the ordering of the A cations in the type and ordering of the Fe-coordination polyhedra in three compounds of the series with the general formula RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 , and REBa 2 Ca 2 Fe 5 O 13 (RE = Gd, Tb), which correspond to the m and n values 1, 0; 1, 1; and 0, 1, respectively. 17 , 18 …”