The six-layer structure of BaSn 0.9Fe 5.47O 11

Abstract

The crystal structure of BaSn 0.9Fe 5.47O 11 was determined using neutron powder diffraction data and the profile refinement method. The hexagonal compound, space group P 3m1 , has hcc-stacked BaO 3 and O 4 layers. A new building unit for this type of structure is introduced, the Q block with formula Ba 2M 7O 14, consisting of two c-stacked BaO 3 layers and two O 4 layers. Between the BaO 3 and O 4 layers one tetrahedral and one octahedral site is occupied; between the BaO 3 layers there are no other cations. BaSn 0.9Fe 5.47O 11 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 Ba 2Sn 2 M 2+Fe 10O 22 could be prepared, in which a partial substitution of Fe by Ga is possible. The nonstoichiometry of BaSn 0.9Fe 5.47O 11 can be explained by the surplus of positive charge if the available tetrahedral and octahedral sites of the structure are completely occupied with Sn 4+ and Fe 3+. To achieve charge compensation either the occupation rates of Sn 4+ and Fe 3+ have to be lowered or a divalent ion has to be introduced, as is effected in the isomorphs.