The superstructure of KCuCe2Se6 due to ordering of copper cations

The quaternary compound KCuCe2Se6 was obtained as black needlelike crystals by reacting a mixture of K2Se, Cu, Ce and Se in a 2:1:1:8 ratio at 450 deg rees C. The compound crystallizes in the orthorhombic space group Fddd with a = 8.5907(5), b = 113962(8) and c = 44.490(3) Angstrom which is a superst ructure of the already published structure of KCuCe2Se6 which was described in space group Immm. The Ce3+ ions are in bicapped distorted trigonal pris matic coordination of Se atoms and the Cu+ ions are in tetrahedral environm ent. The prisms are connected via triangular faces forming rods parallel to the crystallographic a axis, These rods are joined by one capping Se atom and one Se center of the triangular faces thus leading to the formation of anionic layers [CuCe2Se6](n)(n-) within the ab plane. The Cu+ ions occupy o nly one half of the tetrahedral sites in an ordered fashion in contrast to the statistical occupation reported for the substructure. The charge balanc ing K+ ions are located between the anionic layers.