Structural analysis of R2Fe17-xAlxC1 (R=Y,Pr,Tb,Ho,Er; x=2,4) alloys by neutron diffraction

The structures of R2Fe17-xAlxC1 (R=Y,Pr,Tb,Ho,Er; x=2,4) have been studied with neutron diffraction. All of the compounds have the rhombohedral Th2Zn17 structure (space group R-3m) except for the Er series which has the disordered hexagonal Th2Ni17 structure (space group P 63/mmc). Both substitution of Fe and interstitial C can trigger the structure change from hexagonal to rhombohedral in the heavy rare-earth 2:17 compounds. In the rhombohedral compounds, Al is found to prefer the 18h site and fills up the 6c site more rapidly at higher Al concentration. No Al is found at the 9d site. C is mainly found at the 9e site. In the Pr compounds, a small amount of C is also found at the 18g site. In the Er samples, Al is found at the Fe 6g site which is the equivalent of the 9d site in the rhombohedral structure. (orig.)