Pb4Sr13Fe24O53 : an original terrace structure, related to Sr4- xPbxFe6O13- δ

Abstract The Pb for Sr substitution in Sr 4 Fe 6 O 13± δ evidenced a limited existence range of solid solution Sr 4− x Pb x Fe 6 O 13− δ , with x ⩽ 0.7 . For higher lead content, an original phase has been discovered for the composition Pb 4 Sr 13 Fe 24 O 53 with a terrace-like structure. The cell is monoclinic and the parameters refined from the powder X-ray diffraction data are a T = 35.039 ( 2 ) A , b T = 5.5897 ( 2 ) A , c T = 25.662 ( 2 ) A and β = 98 ° 102 ( 2 ) , space group Cc or C2/c. The reconstruction of the reciprocal space allowed describing the structure from a monoclinic sub-cell with different sets of modulation vectors. The high resolution electron microscopy showed that the new phase has a terrace-like structure corresponding to the formation of two types of ribbons parallel to the [302] sub direction. One ribbon is made of 2212-type bricks, 3 / 2 a → sub large, and the second is made of 2201-type bricks, 2 a → sub large. The new structure is therefore described as the intergrowth of 2201-type slices, m octahedra large, and 2212-type slices, n octahedra large. It is therefore the m = 4 and n = 3 member of a large new structural family [Fe 2 (Sr 2 )FeO 6.5±1/2 δ ] 2201 m [Fe 2 (Sr 3− x A 2+ x )Fe 2 O 9.5±1/2 δ ] 2212 n . The magnetic measurements evidence an anti-ferromagnetic-like magnetic transition at T ≈ 730 K showing that the samples, as the Sr 4− x Pb x Fe 6 O 13− δ , ones are magnetic at room temperature.