Synthesis and structural characterisation of the new K2NiF4-type phases, A2In0.5Sb0.5O4(A = Sr, Ba)

In this paper the synthesis and structural characterisation of two new K2NiF4-type phases, Ba2In(0.5)Sb(0.5)O4 and Sr2In(0.5)Sb(0.5)O4, are reported. These are the first examples of K2NiF4 compounds of general formula A2MIII(0.5)M'(V)(0.5)O4 with both 3+ and 5+ cations in the octahedral sites. Ba2In(0.5)Sb(0.5)O4 is shown to have a tetragonal cell [space group I4/mmm, a= 4.1651(1), c= 13.299(1) A] with an essentially disordered arrangement of In and Sb. In the case of Sr2In(0.5)Sb(0.5)O4, however, ordering of In and Sb is observed leading to an expanded unit cell [Pmcb, a= 5.7592(1), b= 5.7740(1), c= 12.543(1) A]. The results therefore show that varying the size of the alkaline earth cation has a pronounced effect on the ordering of In and Sb within the structure.