Crystallographic phase transition within the magnetically ordered state of Ce 2 Fe 17

X-ray diffraction experiments were performed on polycrystalline and single-crystal specimens of Ce{sub 2}Fe{sub 17} at temperatures between 10 and 300 K. Below T{sub t}=118{+-}2 K, additional weak superstructure reflections were observed in the antiferromagnetically ordered state. The superstructure can be described by a doubling of the chemical unit cell along the c direction in hexagonal notation with the same space group R3m as the room-temperature structure. The additional antiferromagnetic satellite reflections observed in earlier neutron diffraction experiments can be conclusively related to the appearance of this superstructure.