Crystal Structure and Magnetism of the 6H Hexagonal Double Perovskites Ba₂FeSbO₆ and Ba₂CoSbO_6–δ: A Neutron Diffraction and Mössbauer Spectroscopy Study

Abstract

Ba 2 MSbO 6-δ (M = Fe, Co) double perovskites have been prepared in polycrystalline form by the solid-state reaction in air and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD), magnetic measurements and Möss-bauer spectroscopy (for M = Fe). At room temperature, the crystal structure of both compounds can be defined as a 6-layered (6H) hexagonal perovskite structure (space group P6 3 /mmc), with a = 5.7875(1) Å and c = 14.2104(2) Å for M = Fe and a = 5.7548(2) Å and c = 14.1439(7) Å for M = Co. M and Sb cations are randomly distributed over 4f and 2a Wickoff positions. The crystal structure is constituted by dimer units of (M,Sb) 4f O 6 octahedra sharing a face along the c axis; the dimers, which sharing corners, are connected by a single layer of (M,Sb) 2a O 6 octahedra. A severe degree of antisite disordering was detected in the Fe compound, which indicates the presence of 52.8 % Fe:47.2 % Sb at the (Fe,Sb) 2a positions, whereas for Co, 64.0 % Sb is present at the (Co,Sb) 2a sites. Mössbauer spectroscopic data for Ba 2 FeSbO 6

Substitution effects on orbital ordering and multiferroicity in some perovskite-like candidates for advanced functional materials

“…Recently, an oxide with Ba 2 CrMoO 6 stoichiometry was shown to exhibit this hexagonal 6H perovskite structure [20] and the new Sb-containing perovskites Ba 2 MSbO 6 (M=Fe, Co) considered here, belong to the same structural polytype [21]. 5 shows Mössbauer spectra of Ba 2 FeSbO 6 confirming the existence of two distinct crystallographic sites for Fe 3+ .…”

Structural Disorder and Classical Spin-Glass Behaviour in Ba3Fe2SbO9

“…Based on tolerance factor calculations Sb 5þ is a good candidate cation likely to give a 6H-type hexagonal perovskite phase. Although a 6H-type perovskite Ba 2 Fe 3þ SbO 6 (Ba 3 Fe 1.5 Sb 1.5 O 9 ) has been reported previously, [2,3,7] the Fe-rich oxidised form Ba 3 Fe 2 3.5þ SbO 9 has never been prepared to the best of our knowledge.…”

“…6H-Type perovskites are particularly favoured when A is large (i.e. A ¼ Ba) and when one-third of the Fe is replaced by another metal cation M. [2][3][4][5][6][7] This allows, in principle, a regular ordering of Fe on the face-sharing dimer sites and the substituting metal on the corner-sharing MO 6 sites.…”

“…[14] Dilution of the magnetic Fe lattice with M ions often gives rise to spin-glass behaviour when partial Fe/M site disorder exists. [3,6,7,15] A further factor that needs to be considered when studying the relationships between magnetic and structural behaviour in 6H-type perovskite ferrites is oxygen stoichiometry. Like cubic perovskites, the 6H-type perovskites can tolerate some oxygen deficiency, though usually over a much smaller range of x.…”

Synthesis and crystal structure of a novel layered barium antimonate Ba2Sb7O13(OH) with mixed-valence antimony

“…The average Ba-O distance has a larger value of 3.023(10) Å than most of other Ba-containing antimonates[21][22][23], which indicates that the Ba 2+ is "loosely" bound in the Sb-O cage and the Sb-O framework has strong covalent bonding characteristic. Moreover, the bond valence analyses performed on Ba give a less BVS value of 1.79 than its normal valence, indicating that the volume of the Sb-O cage is large enough to fully accommodate one Ba cation.…”