CRYSTAL-STRUCTURES OF A CESIUM IRON(III) PHOSPHATE, CS3FE4(PO4)5, AND A CESIUM IRON(III) OXYPHOSPHATE, CS7FE7(PO4)8O2

The reaction of FePO//4 with molten CsCl produces Cs//3Fe//4(PO//4)//5, Cs//7Fe//7(PO//4)//8O//2, or Fe//2O//3, depending on the length of the reaction. The crystal structure of Cs//3Fe//4(PO//4)//5 consists of an interlocking network of corner-sharing phosphate tetrahedra and iron trigonal bipyramids with cesium atoms situated in tunnels. The Cs//7Fe//7(PO//4)//8O//2 structure can be described as a three-dimensional array containing linked phosphate tetrahedra and iron octahedra, trigonal bipyramids, and square pyramids. In addition to the phosphate oxygen atoms, three of the iron polyhedra share a common oxide ion. The cesium atoms are located in tunnels.