Revisiting the crystal structure of the Y0.9Ba1.7Ca2.4Fe5O13 layered-type perovskite: New interplay of the cation ordering & the modulation of the anion sublattice

Abstract

Oxides of the Ln0.8-xBa0.8Ca0.4+xFe2O6-δ (Ln = Gd3+, Tb3+) systems present layered-perovskite structure associated to layered ordering of Ln3+, Ba2+ and Ca2+ in combination with layered ordering of different oxygen-environments of the Fe atoms. The compounds with formula corresponding to x = 0, 0.25 and 0.4 do not contain anion vacancies but a stoichiometric oxygen sublattice, resulting the homologous series A3m+5nFe3m+5nO8m+13n (A = Ln, Ba, Ca) with m, n = 1, 0; 1, 1; and 0, 1 respectively. The nature and ratio of the cations highly influence their ordering and the Fe-coordination polyhedra. In this sense, substitution of Ln3+ by Y3+ in the A3m+5nFe3m+5nO8m+13n oxides might modify the A-layered ordering and/or the oxygen sublattice. Y0.9Ba1.7Ca2.4Fe5O13, instead of stoichiometric YBa2Ca2Fe5O13, is prepared as single phase by ceramic method. Its characterization by means of transmission electron microscopy techniques indicates that, like in the LnBa2Ca2Fe5O13 oxides, the Y3+, Ba2+ and Ca2+ are ordered within five different (00l)-layers in combination with the ordering of the oxygen-polyhedra around the Fe-atoms in square-based pyramids, octahedra and tetrahedra along the c-axis. However, a different superstructure with 2apx22bpx10cp unit cell, ascribed to the modulation of the [FeO4] tetrahedra within the (00l)-layers, is concluded for Y0.9Ba1.7Ca2.4Fe5O13.