Crystal structure and magnetic properties of the R6Si4Se17 (R=La and Ce) compounds

► Identification of two novel phases R6Si4Se17 with R=La and Ce. ► Refinement of the crystal structure of Ce6Si4Se17 from the single-crystal XRD data. ► Determination of the low-temperature magnetic properties of Ce6Si4Se17. The crystal structure of the R6Si4Se17 (R=La and Ce) selenides was studied by means of X-ray powder and single crystal diffraction. The magnetic behaviour of the Ce-based compound was determined through SQUID magnetometry. The two materials crystallize with the Ce6Si4S17 structure type (space group P1¯, Pearson symbol aP54). Their unit cells comprise as many as six inequivalent positions of the rare-earth atoms. The compound Ce6Si4Se17 exhibits Curie–Weiss paramagnetism with no hint at any magnetic ordering down to 1.72K. The magnetic susceptibility data indicates that the Ce ions in this compound may have fluctuating valence character.