The six-layer structure of BaSn0.9Fe5.47O11

The crystal structure of BaSn_0.9Fe_5.47O₁₁ was determined using neutron powder diffraction data and the profile refinement method. The hexagonal compound, space group , has hcc-stacked BaO₃ and O₄ layers. A new building unit for this type of structure is introduced, the Q block with formula Ba₂M₇O₁₄, consisting of two c-stacked BaO₃ layers and two O₄ layers. Between the BaO₃ and O₄ layers one tetrahedral and one octahedral site is occupied; between the BaO₃ layers there are no other cations. BaSn_0.9Fe_5.47O₁₁ shows a magnetic behavior with an ordering temperature T_c of 420 K. Starting models for the structure determination were derived from the known structures of hexagonal ferrites and related compounds. Several isomorphs with formula Ba₂Sn₂M²⁺Fe₁₀O₂₂ could be prepared, in which a partial substitution of Fe by Ga is possible. The nonstoichiometry of BaSn_0.9Fe_5.47O₁₁ can be explained by the surplus of positive charge if the available tetrahedral and octahedral sites of the structure are completely occupied with Sn⁴⁺ and Fe³⁺. To achieve charge compensation either the occupation rates of Sn⁴⁺ and Fe³⁺ have to be lowered or a divalent ion has to be introduced, as is effected in the isomorphs.