Cation ordering in Li2M(II)Sn3O8, M(II)=Mn,Zn

New complex oxides with general formula Li2M(II)Sn3O8 (M=Mn,Zn) have been synthesized and studied by powder neutron diffraction. They crystallize in the orthorhombic system, space group Cmc21, Z=12. For Li2MnSn3O8, the lattice constants obtained from the refinement are a=18.3795(6), b=10.6080(3); ; for Li2ZnSn3O8, a=18.2048(8), b= 10.5098(5) and . The structure consists of a hexagonal close packed array of oxygen layers stacked along direction in a sequence (ABCB) in which cations occupy 1/8 of the tetrahedral and 1/2 of the octahedral interstices. The structure can be derived from that of the partially disordered LiFeSnO4 (space group P63mc) described earlier, assuming complete cation ordering. The influence of two antagonistic factors that govern the cation distribution (the electrostatic repulsion between the adjacent high valence cations and the geometrical factor, that accounts for the ionic size) is discussed.