Crystallographic phase transition within the magnetically ordered state of Ce2Fe17

X-ray diffraction experiments were performed on polycrystalline and single-crystal specimens of Ce2Fe17 at temperatures between 10 and 300 K. Below T-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 R(3) over bar m 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.